Resolve viewport dimension features and preserve valid measurements on refresh

docs/viewport-dimensions.md

@@ -34,10 +34,46 @@ user's unit conversion separate from viewport scale. The ordinary `DIMLFAC`
 override remains sufficient for displaying the saved measurement in other CAD
 readers. The data survives DXF/DWG saves and undo/redo.
 
-The dependent association change uses this metadata when viewport scale changes.
+With `DIMASSOC=2`, acquired features attach a dimension to its viewport, each
-This creation change alone creates nonassociative viewport dimensions and leaves
+block instance, and the source entity. Intersections retain both source chains.
-the drawing's `DIMASSOC` setting unchanged. Direct model/paper associations retain
+Source edits and viewport changes update the definition points and recompute
-their existing behavior.
+compensation while preserving explicit user-positioned sheet text and dimension
+style overrides. A successful update invalidates the saved picture block so the
+new geometry and number are rendered and exported. Undo restores both the
+reference data and the previous picture.
+
+Properties reports whether the dimension is associated, partially associated,
+unresolved, broken, or nonassociative. A broken or unsupported required reference
+preserves the entire dimension's last valid appearance and its original records.
+Creating another dimension does not announce geometry changes to its sources.
+
+## Imported references and support limits
+
+The resolver distinguishes the application's vertex/parameter convention from
+imported edge references. Imported start/end and midpoint modes use their edge
+marker and parameter together. The original regression drawing's first-edge
+start/end pair now reproduces its `0.128` measurement. An imported polyline
+endpoint beyond the first edge requires a usable stored point to validate the
+marker; zero/sentinel data cannot establish that identity. Ambiguous imports
+remain unresolved. Imported viewport scale is updated only when existing OCS
+metadata or `ACAD_DIMASSOC_CALC_DIMLFAC` separates compensation from user scaling.
+
+Unsupported cases retain their saved data and appearance:
+
+- Perspective/oblique viewport projections and malformed/missing reference chains.
+- Ambiguous intersections within one batched block; they are not attached to a
+  guessed pair of children. Intersections between separate identified chains work.
+- Array inserts without an addressable instance index, nesting beyond eight levels,
+  and radial measurements of nonuniformly transformed circular geometry.
+- Imported quadrant references whose moved geometry no longer validates the stored
+  point; newly acquired circle/arc quadrants keep their source-local angle.
+- Tangency with no verified solution, two dependent perpendicular/tangent references
+  requiring a coupled solve, unsupported snap modes, and imported measurement data that does not identify the old viewport compensation.
+
+The osnap codes and reference fields follow the
+[Autodesk DIMASSOC reference](https://help.autodesk.com/cloudhelp/2024/ENU/AutoCAD-DXF/files/GUID-C0B96256-A911-4B4D-85E6-EB4AF2C91E27.htm).
+The restricted imported-marker interpretation above is validated by fixtures;
+it is not a claim that every exporter uses an interchangeable marker scheme.
 
 ## Validation
 
@@ -46,3 +82,17 @@ commits for all five commands, object picks, input retries, active positive and
 negative style factors, exploded dimensions, undo/redo, DXF/DWG persistence,
 clipping, overlapping viewports, pan, scale, and twist. These are headless tests;
 they do not establish visual acceptance in the desktop UI.
+
+Association tests also exercise regeneration, nearest and quadrant parameters,
+angular arc/polyline object picks, spline tangency,
+perpendicularity under nonuniform block scale, nested paths, intersection source
+edits, preserved overrides, erased sources, copy detachment, saved picture
+invalidation, and history. The checked-in DXF fixture is exercised directly.
+The original private drawing can be checked separately:
+
+```powershell
+$env:OPENCAD_VIEWPORT_REGRESSION_DXF = 'C:\path\to\115448.dxf'
+cargo test --locked --offline --lib viewport_dimension_original -- --ignored --nocapture
+```
+
+Do not treat passing headless checks as completed desktop visual acceptance.

src/app/dim_viewport.rs

@@ -208,7 +208,9 @@ impl OpenCADStudio {
         i: usize,
         dimension: Handle,
     ) -> Vec<Option<AcceptedSnap>> {
-        let slots = self.tabs[i].scene.dimension_association_slot_points(dimension);
+        let slots = self.tabs[i]
+            .scene
+            .dimension_association_slot_points(dimension);
         if slots.is_empty() {
             return Vec::new();
         }
@@ -220,7 +222,12 @@ impl OpenCADStudio {
                 let snap = measuring.get(index)?.clone();
                 let frame = snap.frame?;
                 let slot = DVec3::new(slot.x, slot.y, slot.z);
-                if snap.paper_point.truncate().distance_squared(slot.truncate()) <= 1e-12 {
+                if snap
+                    .paper_point
+                    .truncate()
+                    .distance_squared(slot.truncate())
+                    <= 1e-12
+                {
                     return Some(snap);
                 }
                 Some(AcceptedSnap {
@@ -235,9 +242,8 @@ impl OpenCADStudio {
     /// Record the viewport association for a dimension that has just been
     /// committed while measuring through a layout viewport.
     ///
-    /// Announces the whole chain — the viewport, every INSERT on the block
+    /// The stored reference chains establish dependencies. Only the new
-    /// path and the source entity — so the dependency index picks the new
+    /// dimension needs a render update; its sources have not changed.
-    /// association up immediately.
     pub(crate) fn attach_viewport_dimension_association(&mut self, i: usize, dimension: Handle) {
         let snaps = self.viewport_dimension_snaps(i, dimension);
         if snaps.iter().flatten().all(|snap| snap.source.is_none()) {
@@ -246,17 +252,8 @@ impl OpenCADStudio {
         self.tabs[i]
             .scene
             .attach_viewport_dimension_association(dimension, &snaps);
-        let mut changes = vec![(dimension, crate::scene::ChangeKind::Modified)];
+        self.tabs[i]
-        changes.extend(
+            .scene
-            self.tabs[i]
+            .bump_entities(&[(dimension, crate::scene::ChangeKind::Modified)]);
-                .scene
-                .dimension_association_sources(dimension)
-                .into_iter()
-                .map(|handle| (handle, crate::scene::ChangeKind::Modified)),
-        );
-        changes.sort_by_key(|(handle, _)| handle.value());
-        changes.dedup_by_key(|(handle, _)| handle.value());
-        self.tabs[i].scene.bump_entities(&changes);
     }
-
 }

src/app/properties.rs

@@ -1277,6 +1277,24 @@ impl OpenCADStudio {
                                     &self.tabs[i].scene.document,
                                     d.base().common.handle,
                                 );
+                            let statuses = self.tabs[i].scene.dimension_association_status(d.base().common.handle);
+                            let slots = self.tabs[i].scene.dimension_association_slot_points(d.base().common.handle).len();
+                            let status = if statuses.is_empty() {
+                                t!("Nonassociative")
+                            } else if statuses.iter().any(|(_, status)| matches!(status, crate::scene::ReferenceStatus::Broken(_))) {
+                                t!("Broken reference")
+                            } else if statuses.iter().any(|(_, status)| matches!(status, crate::scene::ReferenceStatus::Unresolved)) {
+                                t!("Unresolved reference")
+                            } else if statuses.len() < slots {
+                                t!("Partially associated")
+                            } else {
+                                t!("Associated")
+                            };
+                            general.props.push(crate::scene::model::object::Property {
+                                label: t!("Association status").into_owned(),
+                                field: "association_status",
+                                value: crate::scene::model::object::PropValue::ReadOnly(status.into_owned()),
+                            });
                             general.props.push(crate::scene::model::object::Property {
                                 label: t!("Associative").into_owned(),
                                 field: "associative",

src/app/update/viewport_snap.rs

@@ -137,35 +137,73 @@ impl OpenCADStudio {
         true
     }
 
-    /// Replace a snap source that is a block INSTANCE with the entity inside
+    /// Resolve the instance path once, when a feature is accepted. Failure
-    /// it that actually owns the snapped feature, plus the INSERT path.
+    /// drops source identity so a failed descent cannot attach to the insert's
-    ///
+    /// origin. Ambiguous intersections within one batched block remain unlinked.
-    /// The snap engine can only report what the wire carries, and the
-    /// renderer stamps every wire of an expanded block with the *top-level
-    /// INSERT's* handle — nested inserts included. `SnapSourceRef` promises
-    /// the innermost entity in `source.handle` and the instance chain in
-    /// `block_path`, so the descent happens here, once, at accept time (not
-    /// per pointer move).
-    ///
-    /// When the descent cannot identify the inner entity the source stays the
-    /// INSERT with an empty path. See
-    /// [`crate::scene::Scene::resolve_block_snap_source`] for exactly when
-    /// that happens; the resulting association is coarser (it tracks the whole
-    /// block instance) but never wrong.
     fn resolve_source_block_path(&self, tab: usize, accepted: &mut AcceptedSnap) {
+        let resolve = |source: &mut crate::scene::viewport_ref::SnapSourceRef| {
+            if !source.block_path.is_empty() {
+                return true;
+            }
+            if !matches!(
+                self.tabs[tab]
+                    .scene
+                    .document
+                    .get_entity(source.source.handle),
+                Some(acadrust::EntityType::Insert(_))
+            ) {
+                return true;
+            }
+            if source.snap_type == SnapType::Insertion {
+                let Some(acadrust::EntityType::Insert(insert)) = self.tabs[tab]
+                    .scene
+                    .document
+                    .get_entity(source.source.handle)
+                else {
+                    return false;
+                };
+                let origin = glam::DVec3::new(
+                    insert.insert_point.x,
+                    insert.insert_point.y,
+                    insert.insert_point.z,
+                );
+                return origin.distance(accepted.model_point) < 1e-5;
+            }
+            let Some((entity, path)) = self.tabs[tab].scene.resolve_measurable_feature(
+                source.source.handle,
+                accepted.model_point,
+                accepted.viewport,
+                Some(source.snap_type),
+            ) else {
+                return false;
+            };
+            let distance = crate::scene::viewport_dim_seam::feature_pick_distance(
+                &entity,
+                accepted.model_point,
+                Some(source.snap_type),
+            );
+            if !distance.is_some_and(|distance| distance < 1e-5) {
+                return false;
+            }
+            source.source =
+                crate::command::DimensionAssociationSource::inferred(entity.common().handle);
+            source.block_path = path;
+            true
+        };
         let Some(source) = accepted.source.as_mut() else {
             return;
         };
-        if !source.block_path.is_empty() {
+        if !resolve(source) {
+            accepted.source = None;
             return;
         }
-        if let Some((entity, path)) = self.tabs[tab]
+        if let Some(other) = source.intersection.as_mut() {
-            .scene
+            if !resolve(other)
-            .resolve_block_snap_source(source.source.handle, accepted.model_point)
+                || (other.source.handle == source.source.handle
-        {
+                    && other.block_path == source.block_path)
-            source.source =
+            {
-                crate::command::DimensionAssociationSource::inferred(entity);
+                source.intersection = None;
-            source.block_path = path;
+            }
         }
     }
 

src/app/viewport_dimension_tests.rs

@@ -239,11 +239,20 @@ fn viewport_dimension_linear_aligned_and_radial_object_picks() {
 #[test]
 fn viewport_dimension_angular_preserves_angle_without_length_factor() {
     let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    app.tabs[i].scene.set_current_layout("Model".into());
+    let vertical = app.tabs[i]
+        .scene
+        .add_entity(EntityType::Line(Line::from_points(
+            Vector3::ZERO,
+            Vector3::new(0.0, 100.0, 0.0),
+        )));
+    app.tabs[i].scene.set_current_layout("Dimensions".into());
     let _ = app.dispatch_command("DIMANGULAR");
     let _ = app.feed_command(StepInput::Enter);
     point(&mut app, frame, line, DVec3::ZERO);
     point(&mut app, frame, line, DVec3::X * 100.0);
-    point(&mut app, frame, line, DVec3::Y * 100.0);
+    point(&mut app, frame, vertical, DVec3::Y * 100.0);
     let _ = app.feed_command(StepInput::Point(DVec3::new(70.0, 70.0, 0.0)));
     let doc = &app.tabs[app.active_tab].scene.document;
     assert!((dimension(doc).measurement() - 90.0).abs() < 1e-5);
@@ -377,3 +386,712 @@ fn viewport_dimension_exploded_commit_uses_compensated_text_and_undo() {
         .entities()
         .any(|e| matches!(e, EntityType::Text(_) | EntityType::MText(_))));
 }
+
+#[test]
+fn viewport_dimension_association_scale_edit_picture_and_history() {
+    use crate::scene::ChangeKind;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    finish_aligned(&mut app, line, frame);
+    let handle = dimension(&app.tabs[i].scene.document).base().common.handle;
+    assert_eq!(
+        app.tabs[i].scene.dimension_association_status(handle).len(),
+        2
+    );
+    let Some(EntityType::Dimension(d)) = app.tabs[i].scene.document.get_entity_mut(handle) else {
+        panic!()
+    };
+    d.base_mut().text_user_positioned = true;
+    d.base_mut().text_middle_point = Vector3::new(250.0, 200.0, 0.0);
+    d.base_mut().block_name = "*SavedPicture".into();
+    let pending = app.begin_undo(i, "Viewport scale", 1, true).unwrap();
+    let before = app.tabs[i].scene.document.get_entity_arc(frame.viewport);
+    app.tabs[i].scene.record_undo_before(frame.viewport, before);
+    let Some(EntityType::Viewport(vp)) = app.tabs[i].scene.document.get_entity_mut(frame.viewport)
+    else {
+        panic!()
+    };
+    vp.view_height = 500.0;
+    vp.custom_scale = 0.2;
+    app.tabs[i].scene.notify_viewport_changed(frame.viewport);
+    app.commit_undo_delta(i, pending);
+    assert!((displayed(&app.tabs[i].scene.document) - 100.0).abs() < 1e-5);
+    assert!((dimension(&app.tabs[i].scene.document).measurement() - 20.0).abs() < 1e-5);
+    assert!(dimension(&app.tabs[i].scene.document)
+        .base()
+        .block_name
+        .is_empty());
+    assert_eq!(
+        dimension(&app.tabs[i].scene.document)
+            .base()
+            .text_middle_point,
+        Vector3::new(250.0, 200.0, 0.0)
+    );
+    app.undo_steps(1);
+    assert!((dimension(&app.tabs[i].scene.document).measurement() - 10.0).abs() < 1e-5);
+    assert_eq!(
+        dimension(&app.tabs[i].scene.document).base().block_name,
+        "*SavedPicture"
+    );
+    app.redo_steps(1);
+    assert!((displayed(&app.tabs[i].scene.document) - 100.0).abs() < 1e-5);
+    let pending = app.begin_undo(i, "Edit source", 1, true).unwrap();
+    let before = app.tabs[i].scene.document.get_entity_arc(line);
+    app.tabs[i].scene.record_undo_before(line, before);
+    let Some(EntityType::Line(source)) = app.tabs[i].scene.document.get_entity_mut(line) else {
+        panic!()
+    };
+    source.end.x = 175.0;
+    app.tabs[i]
+        .scene
+        .bump_entities(&[(line, ChangeKind::Modified)]);
+    app.commit_undo_delta(i, pending);
+    assert!((displayed(&app.tabs[i].scene.document) - 175.0).abs() < 1e-5);
+    let pieces = crate::modules::draw::modify::explode::explode_entity(
+        app.tabs[i].scene.document.get_entity(handle).unwrap(),
+        &app.tabs[i].scene.document,
+    );
+    assert!(
+        pieces.iter().any(
+            |e| matches!(e,EntityType::Text(t) if t.value.contains("175"))
+                || matches!(e,EntityType::MText(t) if t.value.contains("175"))
+        ),
+        "{pieces:?}"
+    );
+    for ext in ["dxf", "dwg"] {
+        let doc = &app.tabs[i].scene.document;
+        let bytes = crate::io::save_to_bytes(doc, ext, doc.version).unwrap();
+        let mut loaded = Scene::new();
+        loaded.document = crate::io::load_bytes(&format!("assoc.{ext}"), bytes).unwrap();
+        loaded.notify_viewport_changed(frame.viewport);
+        assert!((displayed(&loaded.document) - 175.0).abs() < 1e-5, "{ext}");
+        assert_eq!(loaded.dimension_association_status(handle).len(), 2);
+    }
+    app.undo_steps(1);
+    assert!((displayed(&app.tabs[i].scene.document) - 100.0).abs() < 1e-5);
+}
+
+#[test]
+fn viewport_dimension_unsupported_and_erased_sources_keep_last_picture() {
+    use crate::scene::dimension_assoc::{resolve_reference_chain, ReferenceStatus};
+    use acadrust::objects::AssocDimensionReference;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    finish_aligned(&mut app, line, frame);
+    let handle = dimension(&app.tabs[i].scene.document).base().common.handle;
+    let reference = AssocDimensionReference {
+        xrefs: vec![frame.viewport, line],
+        osnap_type: 255,
+        ..Default::default()
+    };
+    assert!(matches!(
+        resolve_reference_chain(&app.tabs[i].scene, &reference, None),
+        Err(ReferenceStatus::Unresolved)
+    ));
+    let previous = app.tabs[i]
+        .scene
+        .document
+        .get_entity(handle)
+        .unwrap()
+        .clone();
+    let Some(EntityType::Viewport(vp)) = app.tabs[i].scene.document.get_entity_mut(frame.viewport)
+    else {
+        panic!()
+    };
+    vp.status.perspective = true;
+    app.tabs[i].scene.notify_viewport_changed(frame.viewport);
+    assert_eq!(
+        app.tabs[i].scene.document.get_entity(handle).unwrap(),
+        &previous
+    );
+    assert!(app.tabs[i]
+        .scene
+        .dimension_association_status(handle)
+        .iter()
+        .all(|(_, s)| *s == ReferenceStatus::Unresolved));
+    let Some(EntityType::Viewport(vp)) = app.tabs[i].scene.document.get_entity_mut(frame.viewport)
+    else {
+        panic!()
+    };
+    vp.status.perspective = false;
+    let pending = app.begin_undo(i, "Erase source", 1, false).unwrap();
+    app.tabs[i].scene.erase_entities(&[line]);
+    app.commit_undo_delta(i, pending);
+    assert_eq!(
+        app.tabs[i].scene.document.get_entity(handle).unwrap(),
+        &previous
+    );
+    assert!(app.tabs[i]
+        .scene
+        .dimension_association_status(handle)
+        .iter()
+        .all(|(_, s)| *s == ReferenceStatus::Broken(line)));
+    app.undo_steps(1);
+    assert!(app.tabs[i]
+        .scene
+        .dimension_association_status(handle)
+        .iter()
+        .all(|(_, s)| *s == ReferenceStatus::Resolved));
+}
+
+#[test]
+fn viewport_dimension_intersection_tracks_both_entities() {
+    use crate::scene::ChangeKind;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    app.tabs[i].scene.set_current_layout("Model".into());
+    let other = app.tabs[i]
+        .scene
+        .add_entity(EntityType::Line(Line::from_points(
+            Vector3::new(60.0, -50.0, 0.0),
+            Vector3::new(60.0, 50.0, 0.0),
+        )));
+    app.tabs[i].scene.set_current_layout("Dimensions".into());
+    let _ = app.dispatch_command("DIMALIGNED");
+    point(&mut app, frame, line, DVec3::ZERO);
+    let mut intersection = hit(frame, line, DVec3::X * 60.0);
+    intersection.snap_type = SnapType::Intersection;
+    intersection.secondary_source = Some(DimensionAssociationSource::inferred(other));
+    assert!(app.record_accepted_snap(i, Some(intersection), Some(frame), intersection.world));
+    let result = app.tabs[i]
+        .active_cmd
+        .as_mut()
+        .unwrap()
+        .on_point(intersection.world);
+    app.sync_dimension_snaps(i);
+    let _ = app.apply_cmd_result(result);
+    let _ = app.feed_command(StepInput::Point(DVec3::new(80.0, 80.0, 0.0)));
+    let handle = dimension(&app.tabs[i].scene.document).base().common.handle;
+    assert!(app.tabs[i]
+        .scene
+        .dimension_association_sources(handle)
+        .contains(&other));
+    assert!((displayed(&app.tabs[i].scene.document) - 60.0).abs() < 1e-5);
+    let Some(EntityType::Line(source)) = app.tabs[i].scene.document.get_entity_mut(other) else {
+        panic!()
+    };
+    source.start.x = 80.0;
+    source.end.x = 80.0;
+    app.tabs[i]
+        .scene
+        .bump_entities(&[(other, ChangeKind::Modified)]);
+    assert!((displayed(&app.tabs[i].scene.document) - 80.0).abs() < 1e-5);
+}
+
+#[test]
+fn viewport_dimension_spline_tangency_is_parallel_and_validated() {
+    use crate::scene::dimension_assoc_chain::{feature_point, osnap, FeatureContext};
+    use acadrust::objects::AssocDimensionReference;
+    let mut spline = acadrust::entities::Spline::new();
+    spline.degree = 2;
+    spline.control_points = vec![
+        Vector3::ZERO,
+        Vector3::new(0.5, 0.0, 0.0),
+        Vector3::new(1.0, 1.0, 0.0),
+    ];
+    spline.knots = vec![0.0, 0.0, 0.0, 1.0, 1.0, 1.0];
+    let entity = EntityType::Spline(spline);
+    let reference = AssocDimensionReference {
+        osnap_type: osnap::TAN,
+        osnap_distance: 0.8,
+        ..Default::default()
+    };
+    let result = feature_point(
+        &CadDocument::new(),
+        &entity,
+        &reference,
+        FeatureContext {
+            hint: Some(Vector3::new(1.0, 1.0, 0.0)),
+            from: Some(Vector3::new(0.0, -1.0, 0.0)),
+        },
+    )
+    .unwrap();
+    assert!(
+        (result.x - 1.0).abs() < 1e-6 && (result.y - 1.0).abs() < 1e-6,
+        "{result:?}"
+    );
+    assert!(feature_point(
+        &CadDocument::new(),
+        &entity,
+        &reference,
+        FeatureContext {
+            hint: None,
+            from: Some(Vector3::new(0.0, 1.0, 0.0))
+        }
+    )
+    .is_none());
+}
+
+#[test]
+#[ignore = "Set OPENCAD_VIEWPORT_REGRESSION_DXF to the original local regression drawing"]
+fn viewport_dimension_original_drawing_keeps_unchanged_measurements() {
+    use crate::scene::ChangeKind;
+    let path = std::env::var("OPENCAD_VIEWPORT_REGRESSION_DXF").expect("regression drawing path");
+    let doc = acadrust::DxfReader::from_file(std::path::Path::new(&path))
+        .unwrap()
+        .read()
+        .unwrap();
+    let mut scene = Scene::new();
+    scene.document = doc;
+    let dimensions: Vec<_> = scene
+        .document
+        .entities()
+        .filter_map(|entity| match entity {
+            EntityType::Dimension(dim) => {
+                Some((dim.base().common.handle, dim.base().actual_measurement))
+            }
+            _ => None,
+        })
+        .collect();
+    let mut sources: Vec<_> = dimensions
+        .iter()
+        .flat_map(|(h, _)| scene.dimension_association_sources(*h))
+        .collect();
+    sources.sort();
+    sources.dedup();
+    scene.bump_entities(
+        &sources
+            .into_iter()
+            .map(|h| (h, ChangeKind::Modified))
+            .collect::<Vec<_>>(),
+    );
+    for (handle, saved) in dimensions {
+        if scene.dimension_association_status(handle).is_empty() {
+            continue;
+        }
+        let EntityType::Dimension(dim) = scene.document.get_entity(handle).unwrap() else {
+            panic!()
+        };
+        let factor = dim_override::real(&dim.base().common.extended_data, dim_override::DIMLFAC)
+            .unwrap_or(1.0)
+            .abs();
+        let result = dim.measurement() * factor;
+        println!(
+            "{:X}: saved={saved:.9}, current={result:.9}, status={:?}",
+            handle.value(),
+            scene.dimension_association_status(handle)
+        );
+        assert!(
+            (result - saved).abs() < 1e-3,
+            "{:X}: {saved} -> {result}",
+            handle.value()
+        );
+    }
+}
+
+#[test]
+fn viewport_dimension_fixture_regenerates_and_tracks_an_intersection() {
+    use crate::scene::ChangeKind;
+    let bytes = include_bytes!("../../tests/fixtures/dim_assoc/viewport_associations.dxf").to_vec();
+    let mut scene = Scene::new();
+    scene.document = crate::io::load_bytes("viewport_associations.dxf", bytes).unwrap();
+    scene.notify_viewport_changed(Handle::new(0x200));
+    // The cubic's tangent from (0,300) touches at u=.75, C=(90,283.125).
+    let EntityType::Spline(spline) = scene.document.get_entity(Handle::new(0x104)).unwrap() else {
+        panic!()
+    };
+    let curve = crate::entities::spline::nurbs3(spline).unwrap();
+    let c = DVec3::from_array(curve.point_at_knot(0.75));
+    let tangent = DVec3::from_array(curve.derivative_at_knot(0.75));
+    assert!((c - DVec3::new(0.0, 300.0, 0.0)).cross(tangent).length() < 1e-8);
+    let measured = |scene: &Scene, handle| {
+        let EntityType::Dimension(d) = scene.document.get_entity(Handle::new(handle)).unwrap()
+        else {
+            panic!()
+        };
+        d.measurement()
+            * dim_override::real(&d.base().common.extended_data, dim_override::DIMLFAC)
+                .unwrap_or(1.0)
+                .abs()
+    };
+    for (handle, expected) in [
+        (0x201, 100.0),
+        (0x202, 50.0),
+        (0x203, 35.355339),
+        (0x204, 141.421356),
+        (0x205, 90.0_f64.hypot(16.875)),
+        (0x206, 80.0),
+        (0x207, 60.0),
+    ] {
+        assert!(
+            (measured(&scene, handle) - expected).abs() < 1e-4,
+            "{handle:X}: {}",
+            measured(&scene, handle)
+        );
+    }
+    let Some(EntityType::Line(line)) = scene.document.get_entity_mut(Handle::new(0x107)) else {
+        panic!()
+    };
+    line.start.x = 80.0;
+    line.end.x = 80.0;
+    scene.bump_entities(&[(Handle::new(0x107), ChangeKind::Modified)]);
+    assert!((measured(&scene, 0x207) - 80.0).abs() < 1e-5);
+    let before = scene
+        .document
+        .get_entity(Handle::new(0x205))
+        .unwrap()
+        .clone();
+    for types in [(1, 255), (8, 9)] {
+        let acadrust::objects::ObjectType::Associative(object) =
+            scene.document.objects.get_mut(&Handle::new(0x304)).unwrap()
+        else {
+            panic!()
+        };
+        let acadrust::objects::AssociativeData::DimensionAssociation(assoc) = &mut object.data
+        else {
+            panic!()
+        };
+        assoc.references[0][0].osnap_type = types.0;
+        assoc.references[1][0].osnap_type = types.1;
+        scene.notify_viewport_changed(Handle::new(0x200));
+        assert_eq!(
+            scene.document.get_entity(Handle::new(0x205)).unwrap(),
+            &before
+        );
+        assert!(scene
+            .dimension_association_status(Handle::new(0x205))
+            .iter()
+            .any(|(_, s)| *s == crate::scene::ReferenceStatus::Unresolved));
+    }
+}
+
+#[test]
+fn viewport_dimension_nearest_parameter_survives_source_stretch() {
+    use crate::scene::ChangeKind;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    let _ = app.dispatch_command("DIMALIGNED");
+    point(&mut app, frame, line, DVec3::ZERO);
+    let mut near = hit(frame, line, DVec3::X * 75.0);
+    near.snap_type = SnapType::Nearest;
+    assert!(app.record_accepted_snap(i, Some(near), Some(frame), near.world));
+    let result = app.tabs[i]
+        .active_cmd
+        .as_mut()
+        .unwrap()
+        .on_point(near.world);
+    app.sync_dimension_snaps(i);
+    let _ = app.apply_cmd_result(result);
+    let _ = app.feed_command(StepInput::Point(DVec3::new(55.0, 80.0, 0.0)));
+    assert!((displayed(&app.tabs[i].scene.document) - 75.0).abs() < 1e-5);
+    let Some(EntityType::Line(source)) = app.tabs[i].scene.document.get_entity_mut(line) else {
+        panic!()
+    };
+    source.end.x = 200.0;
+    app.tabs[i]
+        .scene
+        .bump_entities(&[(line, ChangeKind::Modified)]);
+    assert!((displayed(&app.tabs[i].scene.document) - 150.0).abs() < 1e-5);
+}
+
+#[test]
+fn viewport_dimension_nested_block_path_survives_edit_and_copy() {
+    use crate::scene::ChangeKind;
+    use acadrust::entities::Insert;
+    use acadrust::tables::BlockRecord;
+    let (mut app, _, frame) = fixture();
+    let i = app.active_tab;
+    let scene = &mut app.tabs[i].scene;
+    let mut inner = BlockRecord::new("Inner");
+    inner.handle = scene.document.allocate_handle();
+    let inner_h = inner.handle;
+    scene.document.block_records.add(inner).unwrap();
+    let mut leaf = Line::from_points(Vector3::ZERO, Vector3::new(20.0, 0.0, 0.0));
+    leaf.common.owner_handle = inner_h;
+    let leaf = scene.document.add_entity(EntityType::Line(leaf)).unwrap();
+    let mut outer = BlockRecord::new("Outer");
+    outer.handle = scene.document.allocate_handle();
+    let outer_h = outer.handle;
+    scene.document.block_records.add(outer).unwrap();
+    let mut nested = Insert::new("Inner", Vector3::new(30.0, 0.0, 0.0));
+    nested.common.owner_handle = outer_h;
+    nested.set_x_scale(3.0);
+    nested.set_y_scale(3.0);
+    nested.rotation = 0.4;
+    let nested = scene
+        .document
+        .add_entity(EntityType::Insert(nested))
+        .unwrap();
+    scene.set_current_layout("Model".into());
+    let mut root = Insert::new("Outer", Vector3::new(20.0, 50.0, 0.0));
+    root.set_x_scale(2.0);
+    root.set_y_scale(2.0);
+    root.rotation = 0.3;
+    let root = scene.add_entity(EntityType::Insert(root));
+    scene.set_current_layout("Dimensions".into());
+    let transform =
+        crate::scene::dimension_assoc_chain::block_transform(&scene.document, &[root, nested]);
+    let model = |x| {
+        let v = transform.apply(Vector3::new(x, 0.0, 0.0));
+        DVec3::new(v.x, v.y, v.z)
+    };
+    let _ = app.dispatch_command("DIMALIGNED");
+    point(&mut app, frame, root, model(0.0));
+    let accepted = app.accepted_snaps()[0].source.as_ref().unwrap();
+    assert_eq!(accepted.source.handle, leaf);
+    assert_eq!(accepted.block_path, vec![root, nested]);
+    point(&mut app, frame, root, model(20.0));
+    let _ = app.feed_command(StepInput::Point(DVec3::new(90.0, 90.0, 0.0)));
+    let handle = dimension(&app.tabs[i].scene.document).base().common.handle;
+    assert!((displayed(&app.tabs[i].scene.document) - 120.0).abs() < 1e-5);
+    let Some(EntityType::Line(source)) = app.tabs[i].scene.document.get_entity_mut(leaf) else {
+        panic!()
+    };
+    source.end.x = 40.0;
+    app.tabs[i]
+        .scene
+        .bump_entities(&[(leaf, ChangeKind::Modified)]);
+    assert!((displayed(&app.tabs[i].scene.document) - 240.0).abs() < 1e-5);
+    let copied = app.tabs[i].scene.copy_entities(
+        &[handle],
+        &crate::command::EntityTransform::Translate(DVec3::new(10.0, 10.0, 0.0)),
+    );
+    assert_eq!(copied.len(), 1);
+    assert!(app.tabs[i].scene.dimension_association(copied[0]).is_none());
+    assert!(app.tabs[i].scene.dimension_association(handle).is_some());
+}
+
+#[test]
+fn viewport_dimension_hidden_border_and_lock_keep_content_available() {
+    let (mut app, _, frame) = fixture();
+    let scene = &mut app.tabs[app.active_tab].scene;
+    let mut layer = acadrust::tables::Layer::new("Viewport frames");
+    layer.flags.off = true;
+    scene.document.layers.add(layer).unwrap();
+    let Some(EntityType::Viewport(vp)) = scene.document.get_entity_mut(frame.viewport) else {
+        panic!()
+    };
+    vp.common.layer = "Viewport frames".into();
+    vp.status.locked = true;
+    let pick = scene
+        .dimension_pick_through_viewport(DVec3::new(55.0, 50.0, 0.0), 0.2)
+        .unwrap();
+    assert!(pick.frame.locked);
+    assert_eq!(pick.frame.viewport, frame.viewport);
+}
+
+#[test]
+fn viewport_dimension_perpendicular_uses_transformed_geometry() {
+    use crate::scene::dimension_assoc::{resolve_reference_chain, ReferenceStatus};
+    use acadrust::entities::Insert;
+    use acadrust::objects::AssocDimensionReference;
+    use acadrust::tables::BlockRecord;
+    let mut scene = Scene::new();
+    let mut block = BlockRecord::new("Stretched");
+    block.handle = scene.document.allocate_handle();
+    let owner = block.handle;
+    scene.document.block_records.add(block).unwrap();
+    let mut source = Line::from_points(Vector3::ZERO, Vector3::new(10.0, 10.0, 0.0));
+    source.common.owner_handle = owner;
+    let source = scene.document.add_entity(EntityType::Line(source)).unwrap();
+    let mut insert = Insert::new("Stretched", Vector3::ZERO);
+    insert.set_x_scale(2.0);
+    let root = scene.add_entity(EntityType::Insert(insert));
+    let reference = AssocDimensionReference {
+        xrefs: vec![root, source],
+        osnap_type: 8,
+        osnap_point: Vector3::new(4.0, 2.0, 0.0),
+        ..Default::default()
+    };
+    let result =
+        resolve_reference_chain(&scene, &reference, Some(Vector3::new(0.0, 10.0, 0.0))).unwrap();
+    assert!(
+        (result.model.x - 4.0).abs() < 1e-8 && (result.model.y - 2.0).abs() < 1e-8,
+        "{result:?}"
+    );
+    let unrelated = scene.add_entity(EntityType::Line(Line::from_points(
+        Vector3::ZERO,
+        Vector3::UNIT_X,
+    )));
+    let invalid = AssocDimensionReference {
+        xrefs: vec![root, unrelated],
+        ..reference
+    };
+    assert!(matches!(
+        resolve_reference_chain(&scene, &invalid, None),
+        Err(ReferenceStatus::Unresolved)
+    ));
+}
+
+#[test]
+fn viewport_dimension_refresh_preserves_explicit_overrides() {
+    use acadrust::xdata::XDataValue;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    finish_aligned(&mut app, line, frame);
+    let handle = dimension(&app.tabs[i].scene.document).base().common.handle;
+    let entity = app.tabs[i].scene.document.get_entity_mut(handle).unwrap();
+    dim_override::set_on_entity(
+        entity,
+        dim_override::DIMLFAC,
+        Some(XDataValue::Real(-254.0)),
+    );
+    dim_override::set_on_entity(entity, dim_override::DIMTOL, Some(XDataValue::Integer16(1)));
+    dim_override::set_on_entity(entity, dim_override::DIMTP, Some(XDataValue::Real(0.05)));
+    dim_override::set_on_entity(entity, dim_override::DIMTM, Some(XDataValue::Real(0.02)));
+    if let EntityType::Dimension(d) = entity {
+        crate::entities::dimension::set_dimension_text_override(d.base_mut(), Some("L=<>".into()));
+    }
+    let expected = displayed(&app.tabs[i].scene.document);
+    let Some(EntityType::Viewport(vp)) = app.tabs[i].scene.document.get_entity_mut(frame.viewport)
+    else {
+        panic!()
+    };
+    vp.view_height = 500.0;
+    vp.custom_scale = 0.2;
+    app.tabs[i].scene.notify_viewport_changed(frame.viewport);
+    let d = dimension(&app.tabs[i].scene.document);
+    assert!(
+        (displayed(&app.tabs[i].scene.document) - expected).abs() < 1e-5,
+        "{} vs {expected}",
+        displayed(&app.tabs[i].scene.document)
+    );
+    assert_eq!(
+        crate::entities::dimension::dimension_text_override(d.base()),
+        Some("L=<>")
+    );
+    assert_eq!(
+        dim_override::real(&d.base().common.extended_data, dim_override::DIMTP),
+        Some(0.05)
+    );
+    assert_eq!(
+        dim_override::real(&d.base().common.extended_data, dim_override::DIMTM),
+        Some(0.02)
+    );
+}
+
+#[test]
+fn viewport_dimension_block_center_keeps_the_circle_source() {
+    use acadrust::entities::Insert;
+    use acadrust::tables::BlockRecord;
+    let (mut app, _, frame) = fixture();
+    let i = app.active_tab;
+    let scene = &mut app.tabs[i].scene;
+    let mut block = BlockRecord::new("Circle block");
+    block.handle = scene.document.allocate_handle();
+    let owner = block.handle;
+    scene.document.block_records.add(block).unwrap();
+    let mut circle = Circle::new();
+    circle.radius = 10.0;
+    circle.common.owner_handle = owner;
+    let circle = scene
+        .document
+        .add_entity(EntityType::Circle(circle))
+        .unwrap();
+    // This line is closer to the circle center than its circumference is.
+    let mut line = Line::from_points(Vector3::new(-2.0, 1.0, 0.0), Vector3::new(2.0, 1.0, 0.0));
+    line.common.owner_handle = owner;
+    scene.document.add_entity(EntityType::Line(line)).unwrap();
+    scene.set_current_layout("Model".into());
+    let root = scene.add_entity(EntityType::Insert(Insert::new(
+        "Circle block",
+        Vector3::new(40.0, 20.0, 0.0),
+    )));
+    scene.set_current_layout("Dimensions".into());
+    let mut center = hit(frame, root, DVec3::new(40.0, 20.0, 0.0));
+    center.snap_type = SnapType::Center;
+    assert!(app.record_accepted_snap(i, Some(center), Some(frame), center.world));
+    let source = app
+        .accepted_snaps()
+        .last()
+        .unwrap()
+        .source
+        .as_ref()
+        .unwrap();
+    assert_eq!(source.source.handle, circle);
+    assert_eq!(source.block_path, vec![root]);
+}
+
+#[test]
+fn viewport_dimension_angular_object_picks_follow_arc_features() {
+    use crate::scene::{ChangeKind, ReferenceStatus};
+    use acadrust::entities::{Arc, LwPolyline};
+    use acadrust::types::Vector2;
+    for bulged in [false, true] {
+        let (mut app, _, frame) = fixture();
+        let i = app.active_tab;
+        app.tabs[i].scene.set_current_layout("Model".into());
+        let entity = if bulged {
+            let mut poly =
+                LwPolyline::from_points(vec![Vector2::new(100.0, 200.0), Vector2::new(0.0, 300.0)]);
+            poly.vertices[0].bulge = (std::f64::consts::PI / 8.0).tan();
+            EntityType::LwPolyline(poly)
+        } else {
+            let mut arc = Arc::new();
+            arc.center = Vector3::new(0.0, 200.0, 0.0);
+            arc.radius = 100.0;
+            arc.start_angle = 0.0;
+            arc.end_angle = std::f64::consts::FRAC_PI_2;
+            EntityType::Arc(arc)
+        };
+        let source = app.tabs[i].scene.add_entity(entity);
+        app.tabs[i].scene.set_current_layout("Dimensions".into());
+        let _ = app.dispatch_command("DIMANGULAR");
+        let model = DVec3::new(100.0 / 2.0_f64.sqrt(), 200.0 + 100.0 / 2.0_f64.sqrt(), 0.0);
+        let result = app
+            .try_dimension_viewport_entity_pick(i, frame.model_to_paper(model), 0.5)
+            .unwrap();
+        let _ = app.apply_cmd_result(result);
+        assert_eq!(app.accepted_snaps().len(), 3);
+        let _ = app.feed_command(StepInput::Point(DVec3::new(65.0, 85.0, 0.0)));
+        assert!((displayed(&app.tabs[i].scene.document) - 90.0).abs() < 1e-5);
+        let dim = dimension(&app.tabs[i].scene.document).base().common.handle;
+        app.tabs[i].scene.notify_viewport_changed(frame.viewport);
+        assert!((displayed(&app.tabs[i].scene.document) - 90.0).abs() < 1e-5);
+        let status = app.tabs[i].scene.dimension_association_status(dim);
+        assert_eq!(status.len(), 3);
+        assert!(
+            status.iter().all(|(_, s)| *s == ReferenceStatus::Resolved),
+            "{bulged}: {status:?}"
+        );
+        match app.tabs[i].scene.document.get_entity_mut(source).unwrap() {
+            EntityType::Arc(arc) => arc.end_angle = std::f64::consts::PI / 3.0,
+            EntityType::LwPolyline(poly) => {
+                poly.vertices[0].bulge = (std::f64::consts::PI / 12.0).tan()
+            }
+            _ => unreachable!(),
+        }
+        app.tabs[i]
+            .scene
+            .bump_entities(&[(source, ChangeKind::Modified)]);
+        assert!(
+            (displayed(&app.tabs[i].scene.document) - 60.0).abs() < 1e-5,
+            "{bulged}: {}",
+            displayed(&app.tabs[i].scene.document)
+        );
+    }
+}
+
+#[test]
+fn viewport_dimension_quadrant_keeps_its_feature_after_translation() {
+    use crate::scene::ChangeKind;
+    let (mut app, line, frame) = fixture();
+    let i = app.active_tab;
+    app.tabs[i].scene.set_current_layout("Model".into());
+    let mut circle = Circle::new();
+    circle.radius = 100.0;
+    let source = app.tabs[i].scene.add_entity(EntityType::Circle(circle));
+    app.tabs[i].scene.set_current_layout("Dimensions".into());
+    let _ = app.dispatch_command("DIMALIGNED");
+    point(&mut app, frame, line, DVec3::ZERO);
+    let mut quadrant = hit(frame, source, DVec3::X * 100.0);
+    quadrant.snap_type = SnapType::Quadrant;
+    assert!(app.record_accepted_snap(i, Some(quadrant), Some(frame), quadrant.world));
+    let result = app.tabs[i]
+        .active_cmd
+        .as_mut()
+        .unwrap()
+        .on_point(quadrant.world);
+    app.sync_dimension_snaps(i);
+    let _ = app.apply_cmd_result(result);
+    let _ = app.feed_command(StepInput::Point(DVec3::new(60.0, 80.0, 0.0)));
+    let EntityType::Circle(circle) = app.tabs[i].scene.document.get_entity_mut(source).unwrap()
+    else {
+        panic!()
+    };
+    circle.center.x = 300.0;
+    app.tabs[i]
+        .scene
+        .bump_entities(&[(source, ChangeKind::Modified)]);
+    assert!((displayed(&app.tabs[i].scene.document) - 400.0).abs() < 1e-5);
+}

src/scene/dimension_assoc.rs

@@ -14,10 +14,8 @@ use std::f64::consts::TAU;
 
 use crate::command::DimensionAssociationSource;
 
-use super::dimension_assoc_chain::{
+use super::dimension_assoc_chain::{self as chain, ChainError, FeatureContext, ReferenceChain};
-    self as chain, ChainError, FeatureContext, ReferenceChain,
+use super::viewport_ref::{AcceptedSnap, MeasurementScale, ViewportFrame};
-};
-use super::viewport_ref::{AcceptedSnap, ViewportFrame};
 use super::{ChangeKind, Scene};
 
 pub(crate) const POLYLINE_ARC_CENTER_MARKER: i32 = -4;
@@ -404,8 +402,7 @@ impl ChainMap {
     pub(crate) fn model_to_space(&self, point: Vector3) -> Vector3 {
         match &self.frame {
             Some(frame) => {
-                let mapped =
+                let mapped = frame.model_to_paper(glam::DVec3::new(point.x, point.y, point.z));
-                    frame.model_to_paper(glam::DVec3::new(point.x, point.y, point.z));
                 Vector3::new(mapped.x, mapped.y, mapped.z)
             }
             None => point,
@@ -416,8 +413,7 @@ impl ChainMap {
     pub(crate) fn space_to_model(&self, point: Vector3) -> Vector3 {
         match &self.frame {
             Some(frame) => {
-                let mapped =
+                let mapped = frame.paper_to_model(glam::DVec3::new(point.x, point.y, point.z));
-                    frame.paper_to_model(glam::DVec3::new(point.x, point.y, point.z));
                 Vector3::new(mapped.x, mapped.y, mapped.z)
             }
             None => point,
@@ -462,11 +458,18 @@ impl ChainMap {
     /// Only the plane moves: the centre, radius and angles are coordinates
     /// *within* the plane, so they stay as they are and every point the
     /// geometry produces comes out in the dimension's space already.
-    fn map_radial(&self, radial: RadialSourceGeometry) -> RadialSourceGeometry {
+    fn map_radial(&self, radial: RadialSourceGeometry) -> Option<RadialSourceGeometry> {
-        RadialSourceGeometry {
+        let plane = self.map_plane(radial.plane);
-            plane: self.map_plane(radial.plane),
+        let x = glam::DVec3::from_array(plane.x_axis);
-            ..radial
+        let y = glam::DVec3::from_array(plane.y_axis);
+        let magnitude = x.length_squared().max(y.length_squared());
+        if magnitude < 1e-24
+            || (x.length_squared() - y.length_squared()).abs() > magnitude * 1e-9
+            || x.dot(y).abs() > magnitude * 1e-9
+        {
+            return None;
         }
+        Some(RadialSourceGeometry { plane, ..radial })
     }
 }
 
@@ -500,7 +503,9 @@ pub enum ReferenceStatus {
 fn chain_map(scene: &Scene, walked: &ReferenceChain) -> ChainMap {
     ChainMap {
         transform: walked.transform,
-        frame: walked.viewport.and_then(|handle| scene.viewport_frame(handle)),
+        frame: walked
+            .viewport
+            .and_then(|handle| scene.viewport_frame(handle)),
     }
 }
 
@@ -531,7 +536,12 @@ fn hint_error(entity: &EntityType, point: Vector3) -> f64 {
 /// the same drawing. Rather than guess, both readings are mapped down to the
 /// entity and the one that actually lands on the geometry wins. The point is
 /// only ever a *hint* — it disambiguates candidates, it is never the answer.
-fn local_hint(scene: &Scene, map: &ChainMap, entity: &EntityType, stored: Vector3) -> Option<Vector3> {
+fn local_hint(
+    scene: &Scene,
+    map: &ChainMap,
+    entity: &EntityType,
+    stored: Vector3,
+) -> Option<Vector3> {
     let _ = scene;
     let inverse = chain::invert(&map.transform)?;
     let mut candidates = vec![inverse.apply(stored)];
@@ -558,34 +568,66 @@ pub fn resolve_reference_chain(
     let walked = match chain::walk_chain(&scene.document, &reference.xrefs) {
         Ok(walked) => walked,
         Err(ChainError::Missing(handle)) => return Err(ReferenceStatus::Broken(handle)),
-        Err(ChainError::Empty) => return Err(ReferenceStatus::Unresolved),
+        Err(ChainError::Empty | ChainError::Invalid) => return Err(ReferenceStatus::Unresolved),
     };
     let Some(entity) = scene.document.get_entity(walked.entity) else {
         return Err(ReferenceStatus::Broken(walked.entity));
     };
     let map = chain_map(scene, &walked);
-    let inverse = chain::invert(&map.transform);
+    if walked.viewport.is_some() && map.frame.is_none() {
-
+        return Err(ReferenceStatus::Unresolved);
-    let mut local = None;
+    }
-    if chain::evaluates(reference.osnap_type) {
+    let inverse = chain::invert(&map.transform).ok_or(ReferenceStatus::Unresolved)?;
-        let hint = local_hint(scene, &map, entity, reference.osnap_point);
+    if matches!(
-        let from = from_space
+        reference.osnap_type,
-            .zip(inverse)
+        chain::osnap::INTERSEC | chain::osnap::APPARENT_INT
-            .map(|(point, inverse)| inverse.apply(map.space_to_model(point)));
+    ) {
-        local = chain::feature_point(
+        match chain::walk_chain(&scene.document, &reference.intersection_objects) {
+            Err(ChainError::Missing(handle)) => return Err(ReferenceStatus::Broken(handle)),
+            Err(_) => return Err(ReferenceStatus::Unresolved),
+            Ok(_) => {}
+        }
+    }
+    let legacy = reference.main_subent_type != 2
+        && matches!(
+            reference.osnap_type,
+            chain::osnap::NONE | chain::osnap::END | chain::osnap::START_POINT
+        );
+    let local = if reference.osnap_type == chain::osnap::PERP && !walked.block_path.is_empty() {
+        from_space
+            .and_then(|from| {
+                chain::perpendicular_in_model(entity, &map.transform, map.space_to_model(from))
+            })
+            .map(|point| inverse.apply(point))
+    } else if legacy {
+        resolve_local_by_marker(entity, reference)
+    } else if chain::evaluates(reference.osnap_type) {
+        let hint = if reference
+            .osnap_point
+            .x
+            .abs()
+            .max(reference.osnap_point.y.abs())
+            .max(reference.osnap_point.z.abs())
+            < 1e40
+        {
+            local_hint(scene, &map, entity, reference.osnap_point)
+        } else {
+            None
+        };
+        let from = from_space.map(|point| inverse.apply(map.space_to_model(point)));
+        chain::feature_point(
             &scene.document,
             entity,
             reference,
             FeatureContext { hint, from },
-        );
+        )
+    } else {
+        None
+    }
+    .ok_or(ReferenceStatus::Unresolved)?;
+    if !local.x.is_finite() || !local.y.is_finite() || !local.z.is_finite() {
+        return Err(ReferenceStatus::Unresolved);
     }
-    // Every reference — including one whose osnap type we do not evaluate —
-    // falls back to the marker/parameter convention, which is what the
-    // pre-PR3 writer and plain END references use.
-    let local = match local.or_else(|| resolve_local_by_marker(entity, reference)) {
-        Some(local) => local,
-        None => return Err(ReferenceStatus::Unresolved),
-    };
     let model = map.to_model(local);
     Ok(ResolvedReference {
         model,
@@ -798,9 +840,11 @@ pub(crate) fn dimension_is_associative(
         };
         association.dimension == dimension
             && association.associativity != 0
-            && association.references.iter().flatten().any(|reference| {
+            && association
-                chain::walk_chain(document, &reference.xrefs).is_ok()
+                .references
-            })
+                .iter()
+                .flatten()
+                .any(|reference| chain::walk_chain(document, &reference.xrefs).is_ok())
     })
 }
 
@@ -827,6 +871,15 @@ pub(crate) fn constraint_from_associative_dimension(
         };
         (association.dimension == handle && association.associativity != 0).then_some(association)
     })?;
+    if association.trans_space
+        || association
+            .references
+            .iter()
+            .flatten()
+            .any(|r| r.xrefs.len() != 1)
+    {
+        return None;
+    }
     let point = |index: usize| {
         let reference = association.references.get(index)?.first()?;
         Some(ParametricRef::point(
@@ -1207,8 +1260,7 @@ impl Scene {
             self.attach_viewport_radial_association(dimension, snaps);
             return;
         }
-        let mut references: [Vec<AssocDimensionReference>; 4] =
+        let mut references: [Vec<AssocDimensionReference>; 4] = std::array::from_fn(|_| Vec::new());
-            std::array::from_fn(|_| Vec::new());
         let mut associativity = 0;
         let mut trans_space = false;
         let mut reactor_targets = Vec::new();
@@ -1233,25 +1285,41 @@ impl Scene {
             reactor_targets.extend(xrefs.iter().copied());
 
             let osnap_type = chain::osnap_type_for(source.snap_type);
-            // An explicitly-acquired sub-entity wins; otherwise fall back to
+            let local = Self::point_in_entity_space(
-            // the same marker inference model-space creation already uses, in
+                &self.document,
-            // the entity's own coordinates.
+                &source.block_path,
-            let (marker, parameter) = match source.source.marker {
+                dvec3(snap.model_point),
-                Some(marker) => (marker, source.source.parameter),
+            );
-                None => {
+            let marker_parameter = source
-                    let local = Self::point_in_entity_space(
+                .source
-                        &self.document,
+                .marker
-                        &source.block_path,
+                .map(|marker| (marker, source.source.parameter))
-                        dvec3(snap.model_point),
+                .or_else(|| feature_reference(entity, local, source.snap_type));
-                    );
+            let Some((marker, parameter)) = marker_parameter else {
-                    source_reference(entity, local).unwrap_or((0, 0.0))
+                continue;
-                }
             };
+            let mut intersection_objects = Vec::new();
+            if matches!(
+                source.snap_type,
+                crate::snap::SnapType::Intersection | crate::snap::SnapType::ApparentIntersection
+            ) {
+                let Some(other) = source.intersection.as_ref() else {
+                    continue;
+                };
+                intersection_objects.extend(snap.viewport);
+                intersection_objects.extend(other.block_path.iter().copied());
+                intersection_objects.push(other.source.handle);
+                if chain::walk_chain(&self.document, &intersection_objects).is_err() {
+                    continue;
+                }
+                reactor_targets.extend(intersection_objects.iter().copied());
+            }
             associativity |= 1 << index;
             references[index].push(AssocDimensionReference {
                 class_name: "AcDbOsnapPointRef".to_string(),
                 osnap_type,
                 xrefs,
+                intersection_objects,
                 main_subent_type: 1,
                 main_gs_marker: marker,
                 osnap_distance: parameter,
@@ -1385,13 +1453,41 @@ impl Scene {
     /// the erased source comes back and the same query starts answering
     /// [`ReferenceStatus::Resolved`] again, with the reference record itself
     /// never having been rewritten.
-    pub fn dimension_association_status(
+    pub fn dimension_association_status(&self, dimension: Handle) -> Vec<(usize, ReferenceStatus)> {
-        &self,
-        dimension: Handle,
-    ) -> Vec<(usize, ReferenceStatus)> {
         let Some(association) = self.dimension_association(dimension) else {
             return Vec::new();
         };
+        let measurement_supported = !association.trans_space
+            || self.document.get_entity(dimension).is_some_and(|entity| {
+                matches!(
+                    entity,
+                    EntityType::Dimension(Dimension::Angular2Ln(_) | Dimension::Angular3Pt(_))
+                ) || persisted_measurement_scale(&self.document, entity).is_some()
+            });
+        let measurement_supported = measurement_supported
+            && self.document.get_entity(dimension).is_some_and(|entity| {
+                if !matches!(
+                    entity,
+                    EntityType::Dimension(
+                        Dimension::Radius(_) | Dimension::Diameter(_) | Dimension::LargeRadial(_)
+                    )
+                ) {
+                    return true;
+                }
+                association.references[0]
+                    .first()
+                    .and_then(|reference| {
+                        let walked = chain::walk_chain(&self.document, &reference.xrefs).ok()?;
+                        let source = self.document.get_entity(walked.entity)?;
+                        chain_map(self, &walked)
+                            .map_radial(radial_source_for_marker(source, reference.main_gs_marker)?)
+                    })
+                    .is_some()
+            });
+        let measurement_supported = measurement_supported
+            && association.references.iter().flatten()
+                .filter(|r| chain::needs_from_point(r.osnap_type)).count() <= 1;
+        let points = self.dimension_association_slot_points(dimension);
         association
             .references
             .iter()
@@ -1400,8 +1496,16 @@ impl Scene {
                 let reference = slot.first()?;
                 Some((
                     index,
-                    match resolve_reference_chain(self, reference, None) {
+                    match resolve_reference_chain(
-                        Ok(_) => ReferenceStatus::Resolved,
+                        self,
+                        reference,
+                        points
+                            .iter()
+                            .enumerate()
+                            .find_map(|(other, point)| (other != index).then_some(*point)),
+                    ) {
+                        Ok(_) if measurement_supported => ReferenceStatus::Resolved,
+                        Ok(_) => ReferenceStatus::Unresolved,
                         Err(status) => status,
                     },
                 ))
@@ -1437,10 +1541,7 @@ impl Scene {
     }
 
     /// The DIMASSOC payload attached to `dimension`, if there is one.
-    pub fn dimension_association(
+    pub fn dimension_association(&self, dimension: Handle) -> Option<&AssocDimensionAssociation> {
-        &self,
-        dimension: Handle,
-    ) -> Option<&AssocDimensionAssociation> {
         self.document.objects.values().find_map(|object| {
             let ObjectType::Associative(object) = object else {
                 return None;
@@ -1557,12 +1658,8 @@ impl Scene {
         }
     }
 
-    pub(crate) fn infer_dimension_sources(
+    pub(crate) fn infer_dimension_sources(&self, dimension: Handle) -> Vec<Option<Handle>> {
-        &self,
+        let Some(EntityType::Dimension(entity)) = self.document.get_entity(dimension) else {
-        dimension: Handle,
-    ) -> Vec<Option<Handle>> {
-        let Some(EntityType::Dimension(entity)) = self.document.get_entity(dimension)
-        else {
             return Vec::new();
         };
         let radial_data = match entity {
@@ -1659,11 +1756,15 @@ impl Scene {
 
         let mut refreshed = Vec::new();
         for association in associations {
-            // Two passes. PERPENDICULAR and TANGENT are measured *from* the
+            // Dependent snaps need a resolved independent definition point.
-            // other definition point, so the independent references have to
+            // Two such features require a coupled solve; old points are not
-            // land first; a dimension with two dependent references keeps its
+            // evidence of a solution after the geometry changes.
-            // old points as the from-points, which is stable because they were
+            if association.references.iter().flatten()
-            // valid the last time round.
+                .filter(|r| chain::needs_from_point(r.osnap_type)).count() > 1
+            {
+                continue;
+            }
+            // Resolve independent references first, then perpendicular/tangent.
             let mut resolved: [Option<ResolvedReference>; 4] = std::array::from_fn(|index| {
                 let reference = association.references[index].first()?;
                 if chain::needs_from_point(reference.osnap_type) {
@@ -1675,9 +1776,7 @@ impl Scene {
                 .document
                 .get_entity(association.dimension)
                 .and_then(|entity| match entity {
-                    EntityType::Dimension(dimension) => {
+                    EntityType::Dimension(dimension) => Some(dimension_reference_points(dimension)),
-                        Some(dimension_reference_points(dimension))
-                    }
                     _ => None,
                 })
                 .unwrap_or_default();
@@ -1699,6 +1798,19 @@ impl Scene {
                     });
                 resolved[index] = resolve_reference_chain(self, reference, from).ok();
             }
+            if association
+                .references
+                .iter()
+                .enumerate()
+                .any(|(index, slot)| !slot.is_empty() && resolved[index].is_none())
+            {
+                continue;
+            }
+            let viewports: std::collections::HashSet<_> =
+                resolved.iter().flatten().map(|r| r.viewport).collect();
+            if viewports.len() > 1 {
+                continue;
+            }
             // The map of the first live reference governs how the whole
             // dimension is placed and measured — all of a dimension's points
             // are in one space.
@@ -1725,7 +1837,7 @@ impl Scene {
                 // Mapped once, here: everything the match arms below build out
                 // of it then lands in the dimension's own space.
                 Some((
-                    chain_map(self, &walked).map_radial(radial),
+                    chain_map(self, &walked).map_radial(radial)?,
                     reference.osnap_distance,
                 ))
             });
@@ -1738,15 +1850,34 @@ impl Scene {
                     _ => return None,
                 };
                 let radial = radial_source_for_marker(entity, segment)?;
-                Some(chain_map(self, &walked).map_radial(radial))
+                chain_map(self, &walked).map_radial(radial)
             });
             if radial_source.is_none() && resolved.iter().all(Option::is_none) {
                 continue;
             }
+            let Some(before) = self.document.get_entity(association.dimension).cloned() else {
+                continue;
+            };
+            let angular = matches!(
+                &before,
+                EntityType::Dimension(Dimension::Angular2Ln(_) | Dimension::Angular3Pt(_))
+            );
+            let measurement_scale = if let Some(frame) = map.frame.filter(|_| !angular) {
+                let Some(mut scale) = persisted_measurement_scale(&self.document, &before) else {
+                    continue;
+                };
+                scale.viewport_compensation = frame.paper_to_model_length_factor();
+                Some(scale)
+            } else {
+                None
+            };
             if self.is_recording_undo() {
                 let before = self.document.get_entity_arc(association.dimension);
                 self.record_undo_before(association.dimension, before);
             }
+            if measurement_scale.is_some() {
+                self.ensure_app_id(MeasurementScale::APP_ID);
+            }
             let Some(EntityType::Dimension(dimension)) =
                 self.document.get_entity_mut(association.dimension)
             else {
@@ -2005,8 +2136,8 @@ impl Scene {
                         .zip(resolved.iter())
                         .all(|(model, space)| match (model, space, map.frame.as_ref()) {
                             (Some(model), Some(space), Some(frame)) => {
-                                let projected =
+                                let projected = frame
-                                    frame.model_to_paper(glam::DVec3::new(model.x, model.y, model.z));
+                                    .model_to_paper(glam::DVec3::new(model.x, model.y, model.z));
                                 (projected.x - space.x).abs() < 1e-6
                                     && (projected.y - space.y).abs() < 1e-6
                             }
@@ -2015,6 +2146,30 @@ impl Scene {
                 "resolved paper points must be the model points through the frame",
             );
             dimension.base_mut().actual_measurement = measurement;
+            if map.frame.is_some() {
+                if let EntityType::Dimension(old) = &before {
+                    if old.base().text_user_positioned {
+                        dimension.base_mut().text_middle_point = old.base().text_middle_point;
+                        dimension.base_mut().insertion_point = old.base().insertion_point;
+                    }
+                }
+            }
+            let entity = self
+                .document
+                .get_entity_mut(association.dimension)
+                .expect("dimension exists");
+            if let Some(scale) = measurement_scale {
+                scale.write_to_entity(entity);
+            }
+            if *entity == before {
+                continue;
+            }
+            // Saved anonymous blocks bypass generated dimension rendering.
+            // Invalidate only after a completely resolved, committed update;
+            // the undo snapshot above retains the previous picture and data.
+            if let EntityType::Dimension(dimension) = entity {
+                dimension.base_mut().block_name.clear();
+            }
             refreshed.push((association.dimension, ChangeKind::Modified));
         }
         refreshed
@@ -2053,3 +2208,121 @@ fn linear_measurement(linear: &acadrust::entities::DimensionLinear) -> f64 {
     let axis = [linear.rotation.cos(), linear.rotation.sin()];
     ((second[0] - first[0]) * axis[0] + (second[1] - first[1]) * axis[1]).abs()
 }
+
+/// Encode the feature actually acquired, in source-local coordinates.
+fn feature_reference(
+    entity: &EntityType,
+    point: Vector3,
+    kind: crate::snap::SnapType,
+) -> Option<(i32, f64)> {
+    use crate::snap::SnapType as S;
+    match kind {
+        S::Node | S::Insertion => Some((0, 0.0)),
+        S::Center if matches!(entity, EntityType::Ellipse(_)) => Some((-3, 0.0)),
+        S::Endpoint | S::ObjectPick | S::Center => {
+            if kind != S::Center {
+                if let Some(index) = source_points(entity)
+                    .iter()
+                    .position(|candidate| point_distance_squared(*candidate, point) < 1e-12)
+                {
+                    return Some((index as i32, 0.0));
+                }
+            }
+            if matches!(entity, EntityType::Circle(_) | EntityType::Arc(_)) {
+                return source_reference(entity, point);
+            }
+            let planar = crate::entities::curve::entity_curve(entity)?;
+            if let KernelCurve::Polyline(polyline) = &planar.curve {
+                for segment in 0..polyline.vertices.len() {
+                    if let Some(arc) = polyline.segment_arc(segment) {
+                        let center = vector3(planar.plane.point_at(arc.center));
+                        if point_distance_squared(center, point) < 1e-12 {
+                            return Some((POLYLINE_ARC_CENTER_MARKER, segment as f64));
+                        }
+                    }
+                }
+            }
+            None
+        }
+        S::Nearest | S::Extension => {
+            if matches!(entity, EntityType::Circle(_) | EntityType::Arc(_)) {
+                return source_reference(entity, point);
+            }
+            let planar = crate::entities::curve::entity_curve(entity)?;
+            let near = closest_point(&planar.curve, planar.plane.project(dpoint(point))?);
+            Some((0, near.t))
+        }
+        S::Midpoint => {
+            let planar = crate::entities::curve::entity_curve(entity)?;
+            if let KernelCurve::Polyline(_) = &planar.curve {
+                let uv = planar.plane.project(dpoint(point))?;
+                let segments = planar.curve.segments();
+                let (index, _) = segments.iter().enumerate().min_by(|(_, a), (_, b)| {
+                    let error = |c: &KernelCurve| {
+                        let p = closest_point(c, uv).point;
+                        (p[0] - uv[0]).powi(2) + (p[1] - uv[1]).powi(2)
+                    };
+                    error(a).total_cmp(&error(b))
+                })?;
+                Some((index as i32, 0.5))
+            } else {
+                Some((0, 0.5))
+            }
+        }
+        S::Tangent => {
+            if let EntityType::Spline(spline) = entity {
+                return Some((
+                    0,
+                    crate::entities::spline::nurbs3(spline)?.parameter_at(dpoint(point)),
+                ));
+            }
+            source_reference(entity, point)
+        }
+        S::Intersection | S::ApparentIntersection => Some((0, 0.0)),
+        _ => source_reference(entity, point),
+    }
+}
+
+fn persisted_measurement_scale(
+    doc: &acadrust::CadDocument,
+    entity: &EntityType,
+) -> Option<MeasurementScale> {
+    use crate::entities::dim_override;
+    use acadrust::xdata::XDataValue;
+    let EntityType::Dimension(dimension) = entity else {
+        return None;
+    };
+    let data = &dimension.base().common.extended_data;
+    let effective = dim_override::real(data, dim_override::DIMLFAC)
+        .or_else(|| {
+            doc.dim_styles
+                .get(&dimension.base().style_name)
+                .map(|s| s.dimlfac)
+        })?
+        .abs();
+    let effective = if effective == 0.0 { 1.0 } else { effective };
+    if !effective.is_finite() {
+        return None;
+    }
+    if let Some(mut scale) = MeasurementScale::read(data) {
+        // A Properties edit writes the persisted total DIMLFAC. Preserve that
+        // new user choice when the next source/viewport update recomposes it.
+        scale.user_lfac = effective / scale.viewport_compensation;
+        return Some(scale);
+    }
+    let calculated = data
+        .get_record("ACAD_DIMASSOC_CALC_DIMLFAC")?
+        .values
+        .iter()
+        .find_map(|v| match v {
+            XDataValue::Real(v) => Some(v.abs()),
+            _ => None,
+        })?;
+    if !calculated.is_finite() || calculated <= 0.0 {
+        return None;
+    }
+    Some(MeasurementScale {
+        user_lfac: effective / calculated,
+        viewport_compensation: calculated,
+    })
+}

src/scene/dimension_assoc_chain.rs

@@ -37,7 +37,7 @@
 use acadrust::objects::AssocDimensionReference;
 use acadrust::types::{Handle, Matrix4, Transform, Vector3};
 use acadrust::{CadDocument, EntityType};
-use cadkernel::geom2d::{closest_point, Curve as KernelCurve, DEFAULT_SEGMENTS_PER_RADIAN};
+use cadkernel::geom2d::{closest_point, Curve as KernelCurve};
 use cadkernel::space::Plane;
 
 use crate::entities::curve::entity_curve;
@@ -50,7 +50,7 @@ use crate::entities::curve::entity_curve;
 /// and `NEAR` for a point taken at a parameter on a circle, so those two keep
 /// meaning exactly what they used to.
 #[allow(dead_code)] // The full code table is kept so a reader can see what a
-// stored `osnap_type` means, including the modes we pass through untouched.
+                    // stored `osnap_type` means, including the modes we pass through untouched.
 pub(crate) mod osnap {
     pub const NONE: u8 = 0;
     pub const END: u8 = 1;
@@ -115,6 +115,7 @@ pub(crate) struct ReferenceChain {
 pub(crate) enum ChainError {
     /// `xrefs` was empty — nothing to resolve.
     Empty,
+    Invalid,
     /// A handle in the chain names an object that is not in the document
     /// (erased source; restored by an undo).
     Missing(Handle),
@@ -131,55 +132,54 @@ pub(crate) fn walk_chain(
     document: &CadDocument,
     xrefs: &[Handle],
 ) -> Result<ReferenceChain, ChainError> {
+    if xrefs.is_empty() {
+        return Err(ChainError::Empty);
+    }
     let mut viewport = None;
-    let mut block_path: Vec<Handle> = Vec::new();
+    let mut block_path = Vec::new();
-    let mut entity = None;
     let mut transform = Transform::identity();
-
+    let mut owner = None;
-    for (index, handle) in xrefs.iter().copied().enumerate() {
+    for (index, &handle) in xrefs.iter().enumerate() {
         if handle.is_null() {
+            return Err(ChainError::Invalid);
+        }
+        let node = document
+            .get_entity(handle)
+            .ok_or(ChainError::Missing(handle))?;
+        if owner.is_some_and(|owner| node.common().owner_handle != owner) {
+            return Err(ChainError::Invalid);
+        }
+        if index == 0 && matches!(node, EntityType::Viewport(_)) {
+            viewport = Some(handle);
+            owner = document.block_records.get("*Model_Space").map(|b| b.handle);
             continue;
         }
-        let Some(node) = document.get_entity(handle) else {
+        if index == xrefs.len() - 1 {
-            return Err(ChainError::Missing(handle));
+            return Ok(ReferenceChain {
-        };
+                viewport,
-        match node {
+                block_path,
-            // Only a *leading* viewport is the trans-space hop. A viewport
+                entity: handle,
-            // deeper in the chain would be geometry being dimensioned (the
+                transform,
-            // paper-space rectangle itself), so it falls through to `entity`.
+            });
-            EntityType::Viewport(_) if index == 0 && viewport.is_none() => {
-                viewport = Some(handle);
-            }
-            EntityType::Insert(insert) => {
-                block_path.push(handle);
-                transform =
-                    transform.compose(&crate::scene::render_graph::insert_transform(document, insert));
-            }
-            _ => {
-                entity = Some(handle);
-                break;
-            }
         }
+        let EntityType::Insert(insert) = node else {
+            return Err(ChainError::Invalid);
+        };
+        // Arrays need an instance index that this reference format does not carry.
+        if insert.row_count > 1 || insert.column_count > 1 || block_path.contains(&handle) {
+            return Err(ChainError::Invalid);
+        }
+        let block = document
+            .block_records
+            .get(&insert.block_name)
+            .ok_or(ChainError::Invalid)?;
+        owner = Some(block.handle);
+        block_path.push(handle);
+        transform = transform.compose(&crate::scene::render_graph::insert_transform(
+            document, insert,
+        ));
     }
-
+    Err(ChainError::Empty)
-    let entity = match entity {
-        Some(entity) => entity,
-        // Nothing but INSERTs: the innermost one is the geometry, and it is
-        // no longer part of the path leading to it.
-        None => match block_path.pop() {
-            Some(innermost) => {
-                transform = block_transform(document, &block_path);
-                innermost
-            }
-            None => return Err(ChainError::Empty),
-        },
-    };
-    Ok(ReferenceChain {
-        viewport,
-        block_path,
-        entity,
-        transform,
-    })
 }
 
 /// Accumulated entity-local -> model transform for an ordered INSERT path.
@@ -187,8 +187,9 @@ pub(crate) fn block_transform(document: &CadDocument, block_path: &[Handle]) ->
     let mut transform = Transform::identity();
     for handle in block_path {
         if let Some(EntityType::Insert(insert)) = document.get_entity(*handle) {
-            transform =
+            transform = transform.compose(&crate::scene::render_graph::insert_transform(
-                transform.compose(&crate::scene::render_graph::insert_transform(document, insert));
+                document, insert,
+            ));
         }
     }
     transform
@@ -270,7 +271,7 @@ pub(crate) struct FeatureContext {
     /// The point the feature is measured *from*, in entity-local coordinates.
     /// PERPENDICULAR and TANGENT are two-point features: the foot / touch
     /// point only exists relative to an external point, which for a dimension
-    /// is the other definition point. `None` falls back to `hint`.
+    /// is the other definition point. Tangency requires this point.
     pub from: Option<Vector3>,
 }
 
@@ -287,9 +288,12 @@ pub(crate) fn feature_point(
     context: FeatureContext,
 ) -> Option<Vector3> {
     match reference.osnap_type {
+        osnap::END | osnap::START_POINT if reference.main_subent_type == 2 => {
+            imported_endpoint(entity, reference, context.hint)
+        }
         osnap::CEN => center_point(entity, reference),
         osnap::MID => mid_point(entity, reference),
-        osnap::QUAD => quadrant_point(entity, context.hint?),
+        osnap::QUAD => quadrant_point(entity, reference, context.hint?),
         osnap::NODE | osnap::INS => node_point(entity),
         osnap::INTERSEC | osnap::APPARENT_INT => intersection_point(
             document,
@@ -313,7 +317,9 @@ pub(crate) fn feature_point(
 pub(crate) fn evaluates(osnap_type: u8) -> bool {
     matches!(
         osnap_type,
-        osnap::CEN
+        osnap::END
+            | osnap::START_POINT
+            | osnap::CEN
             | osnap::MID
             | osnap::QUAD
             | osnap::NODE
@@ -342,7 +348,13 @@ fn center_point(entity: &EntityType, reference: &AssocDimensionReference) -> Opt
             let KernelCurve::Polyline(polyline) = &planar.curve else {
                 return None;
             };
-            let segment = reference.main_gs_marker.max(0) as usize;
+            let segment = if reference.main_subent_type == 1
+                && reference.main_gs_marker == super::dimension_assoc::POLYLINE_ARC_CENTER_MARKER
+            {
+                reference.osnap_distance.round().max(0.0) as usize
+            } else {
+                segment_index(reference)?
+            };
             let arc = polyline.segment_arc(segment)?;
             Some(lift(&planar.plane, arc.center))
         }
@@ -356,36 +368,52 @@ fn mid_point(entity: &EntityType, reference: &AssocDimensionReference) -> Option
         // without one, the midpoint of the whole run.
         KernelCurve::Polyline(_) if reference.main_gs_marker >= 0 => {
             let segments = planar.curve.segments();
-            let segment = segments.get(reference.main_gs_marker as usize)?;
+            let segment = segments.get(segment_index(reference)?)?;
             Some(lift(&planar.plane, segment.point_at(0.5)))
         }
         _ => Some(lift(&planar.plane, planar.curve.point_at(0.5))),
     }
 }
 
-fn quadrant_point(entity: &EntityType, hint: Vector3) -> Option<Vector3> {
+fn quadrant_point(
+    entity: &EntityType,
+    reference: &AssocDimensionReference,
+    hint: Vector3,
+) -> Option<Vector3> {
     let planar = entity_curve(entity)?;
     let (centre, radius) = match &planar.curve {
         KernelCurve::Circle(circle) => (circle.centre, circle.radius),
         KernelCurve::Arc(arc) => (arc.centre, arc.radius),
         _ => return None,
     };
-    // Four candidates on the curve's own plane; the stored point picks one, so
+    let valid_angle = |angle: f64| match &planar.curve {
-    // a rotated source keeps the quadrant the user actually snapped to.
+        KernelCurve::Arc(arc) => {
+            (angle - arc.start_angle).rem_euclid(std::f64::consts::TAU) <= arc.sweep() + 1e-9
+        }
+        _ => true,
+    };
+    let at_angle = |angle: f64| {
+        lift(
+            &planar.plane,
+            [
+                centre[0] + radius * angle.cos(),
+                centre[1] + radius * angle.sin(),
+            ],
+        )
+    };
+    // New references retain the chosen source-local angle, so translation
+    // cannot silently select another quadrant using the old world point.
+    if reference.main_subent_type == 1 && reference.main_gs_marker == -2 {
+        let angle = reference.osnap_distance;
+        return (angle.is_finite() && valid_angle(angle)).then(|| at_angle(angle));
+    }
+    // An imported point can identify an unchanged quadrant, but cannot prove
+    // which quadrant was intended after it moves away from the stored hint.
     (0..4)
-        .map(|index| {
+        .map(|index| std::f64::consts::FRAC_PI_2 * index as f64)
-            let angle = std::f64::consts::FRAC_PI_2 * index as f64;
+        .filter(|angle| valid_angle(*angle))
-            lift(
+        .map(at_angle)
-                &planar.plane,
+        .find(|candidate| distance_squared(*candidate, hint) < 1e-12)
-                [
-                    centre[0] + radius * angle.cos(),
-                    centre[1] + radius * angle.sin(),
-                ],
-            )
-        })
-        .min_by(|first, second| {
-            distance_squared(*first, hint).total_cmp(&distance_squared(*second, hint))
-        })
 }
 
 fn node_point(entity: &EntityType) -> Option<Vector3> {
@@ -402,7 +430,50 @@ fn node_point(entity: &EntityType) -> Option<Vector3> {
 fn perpendicular_point(entity: &EntityType, from: Vector3) -> Option<Vector3> {
     let planar = entity_curve(entity)?;
     let uv = planar.plane.project(dpoint(from))?;
-    Some(lift(&planar.plane, closest_point(&planar.curve, uv).point))
+    let near = closest_point(&planar.curve, uv);
+    let direction = planar.curve.tangent_at(near.t);
+    let delta = [near.point[0] - uv[0], near.point[1] - uv[1]];
+    let residual = delta[0] * direction[0] + delta[1] * direction[1];
+    if residual.abs() > 1e-8 * delta[0].hypot(delta[1]).max(1.0) {
+        return None;
+    }
+    Some(lift(&planar.plane, near.point))
+}
+
+/// Perpendicularity must be evaluated after a block's nonuniform scale.
+pub(crate) fn perpendicular_in_model(
+    entity: &EntityType,
+    transform: &Transform,
+    from: Vector3,
+) -> Option<Vector3> {
+    use glam::DVec3;
+    let source = entity_curve(entity)?;
+    let origin = transform.apply(vector3(source.plane.origin));
+    let x = DVec3::from_array(dpoint(
+        transform.apply_rotation(vector3(source.plane.x_axis)),
+    ));
+    let y = DVec3::from_array(dpoint(
+        transform.apply_rotation(vector3(source.plane.y_axis)),
+    ));
+    let axis_x = x.try_normalize()?;
+    let normal = x.cross(y).try_normalize()?;
+    let axis_y = normal.cross(axis_x);
+    let plane = Plane::from_axes(dpoint(origin), axis_x.to_array(), axis_y.to_array());
+    let curve = source.curve.transformed(&cadkernel::geom2d::Transform {
+        origin: [0.0, 0.0].into(),
+        x_axis: [x.dot(axis_x), x.dot(axis_y)].into(),
+        y_axis: [y.dot(axis_x), y.dot(axis_y)].into(),
+    })?;
+    let uv = plane.project(dpoint(from))?;
+    let near = closest_point(&curve, uv);
+    let tangent = curve.tangent_at(near.t);
+    let delta = [near.point[0] - uv[0], near.point[1] - uv[1]];
+    if (delta[0] * tangent[0] + delta[1] * tangent[1]).abs()
+        > 1e-8 * delta[0].hypot(delta[1]).max(1.0)
+    {
+        return None;
+    }
+    Some(lift(&plane, near.point))
 }
 
 fn nearest_point(
@@ -416,9 +487,7 @@ fn nearest_point(
     // Every other curve carries the kernel's normalised 0..1 parameter.
     match &planar.curve {
         KernelCurve::Circle(_) | KernelCurve::Arc(_) => match entity {
-            EntityType::Circle(circle) => {
+            EntityType::Circle(circle) => Some(circle.point_at_angle_wcs(reference.osnap_distance)),
-                Some(circle.point_at_angle_wcs(reference.osnap_distance))
-            }
             EntityType::Arc(arc) => Some(arc.point_at_angle_wcs(reference.osnap_distance)),
             _ => None,
         },
@@ -454,39 +523,14 @@ fn tangent_point(
         return spline_tangent_point(spline, reference, context);
     }
     let planar = entity_curve(entity)?;
-    let (centre, radius) = match &planar.curve {
+    let from = context.from?;
-        KernelCurve::Circle(circle) => (circle.centre, circle.radius),
-        KernelCurve::Arc(arc) => (arc.centre, arc.radius),
-        _ => {
-            // Generic curve: no closed form and no spline evaluator. Hold the
-            // stored parameter if there is one, else leave it unresolved.
-            return nearest_point(entity, reference, context.hint);
-        }
-    };
-    let from = context.from.or(context.hint)?;
     let uv = planar.plane.project(dpoint(from))?;
-    let (dx, dy) = (uv[0] - centre[0], uv[1] - centre[1]);
+    cadkernel::geom2d::snap::tangent_from(&planar.curve, uv)
-    let distance = (dx * dx + dy * dy).sqrt();
-    if !distance.is_finite() || distance <= radius + 1e-12 || radius <= 1e-12 {
-        return None;
-    }
-    // Two touch points, symmetric about the centre-to-`from` line.
-    let base = dy.atan2(dx);
-    let offset = (radius / distance).clamp(-1.0, 1.0).acos();
-    let candidates = [base + offset, base - offset].map(|angle| {
-        lift(
-            &planar.plane,
-            [
-                centre[0] + radius * angle.cos(),
-                centre[1] + radius * angle.sin(),
-            ],
-        )
-    });
-    let hint = context.hint.unwrap_or(candidates[0]);
-    candidates
         .into_iter()
-        .min_by(|first, second| {
+        .map(|candidate| lift(&planar.plane, candidate.point))
-            distance_squared(*first, hint).total_cmp(&distance_squared(*second, hint))
+        .min_by(|a, b| {
+            distance_squared(*a, context.hint.unwrap_or(from))
+                .total_cmp(&distance_squared(*b, context.hint.unwrap_or(from)))
         })
 }
 
@@ -504,50 +548,52 @@ fn spline_tangent_point(
         let hint = context.hint.or(context.from)?;
         curve.parameter_at(dpoint(hint)).clamp(start, end)
     };
-    let Some(from) = context.from.or(context.hint) else {
+    let from = glam::DVec3::from_array(dpoint(context.from?));
-        // No external point: the stored parameter is the whole answer.
+    // A tangent is parallel to C(u)-P. Minimize the vector cross product,
-        return Some(vector3(curve.point_at_knot(u)));
+    // which also detects nonplanar curves that have no tangent from P.
-    };
-    let p = dpoint(from);
-    // Newton on f(u) = (C(u) - P) · C'(u). f'(u) is approximated by a central
-    // difference of f, which converges in a handful of steps from a seed that
-    // is already on the right lobe and never leaves the domain.
     let f = |u: f64| {
-        let c = curve.point_at_knot(u);
+        let c = glam::DVec3::from_array(curve.point_at_knot(u));
-        let d = curve.derivative_at_knot(u);
+        let d = glam::DVec3::from_array(curve.derivative_at_knot(u));
-        (c[0] - p[0]) * d[0] + (c[1] - p[1]) * d[1] + (c[2] - p[2]) * d[2]
+        (c - from).cross(d)
     };
-    let span = (end - start).abs().max(1e-12);
+    let span = (end - start).abs();
-    let step = span * 1e-6;
+    if !span.is_finite() || span <= 1e-15 {
-    for _ in 0..24 {
+        return None;
+    }
+    for _ in 0..48 {
         let value = f(u);
-        if value.abs() <= span * 1e-12 {
+        let lo = (u - span * 1e-6).max(start);
+        let hi = (u + span * 1e-6).min(end);
+        let derivative = (f(hi) - f(lo)) / (hi - lo);
+        if !value.is_finite() || !derivative.is_finite() {
+            return None;
+        }
+        if derivative.length_squared() <= 1e-30 {
             break;
         }
-        let slope = (f((u + step).min(end)) - f((u - step).max(start))) / (2.0 * step);
+        let next = (u - value.dot(derivative) / derivative.length_squared()).clamp(start, end);
-        if !slope.is_finite() || slope.abs() < 1e-18 {
+        if (next - u).abs() < span * 1e-14 {
-            break;
-        }
-        let next = (u - value / slope).clamp(start, end);
-        if !next.is_finite() || (next - u).abs() <= span * 1e-14 {
             u = next;
             break;
         }
         u = next;
     }
-    Some(vector3(curve.point_at_knot(u)))
+    let c = glam::DVec3::from_array(curve.point_at_knot(u));
+    let d = glam::DVec3::from_array(curve.derivative_at_knot(u));
+    let scale = (c - from).length() * d.length();
+    if !c.is_finite() || scale <= 1e-20 || f(u).length() > 1e-8 * scale {
+        return None;
+    }
+    Some(vector3(c.to_array()))
 }
 
 // ── Intersection ──────────────────────────────────────────────────────────
 
 /// Intersection of `entity` with the reference's second object chain.
 ///
-/// Both curves are tessellated on the first curve's plane and crossed
+/// Transform both curves into the first entity's local plane and use the
-/// pairwise; the crossing nearest the stored osnap point wins, so a pair of
+/// kernel's exact/converged intersection solver. Apparent intersections may
-/// curves that meet more than once keeps the corner the user picked. With
+/// project noncoplanar curves; only straight lines support an extended crossing.
-/// `apparent` the segment parameters are not clamped, which recovers the
-/// crossing of the two *extended* nearest segments — the best-effort AutoCAD
-/// calls an apparent intersection in a plan view.
 fn intersection_point(
     document: &CadDocument,
     entity: &EntityType,
@@ -555,59 +601,53 @@ fn intersection_point(
     hint: Vector3,
     apparent: bool,
 ) -> Option<Vector3> {
+    let main = walk_chain(document, &reference.xrefs).ok()?;
     let other = walk_chain(document, &reference.intersection_objects).ok()?;
-    let other_entity = document.get_entity(other.entity)?;
+    if main.viewport != other.viewport {
+        return None;
+    }
+    let inverse = invert(&main.transform)?;
     let first = entity_curve(entity)?;
-    let second = entity_curve(other_entity)?;
+    let second = entity_curve(document.get_entity(other.entity)?)?;
-    // The first curve's plane is the working frame. The second curve is
+    let map = |uv| {
-    // evaluated through its *own* block path, so each of its points is lifted
+        let local = inverse.apply(other.transform.apply(lift(&second.plane, uv)));
-    // to model space and then projected back onto that frame before crossing.
+        let projected = first.plane.project(dpoint(local))?;
-    let a = first.curve.tessellate(DEFAULT_SEGMENTS_PER_RADIAN);
+        if !apparent && distance_squared(local, lift(&first.plane, projected)) > 1e-12 {
-    let b = second
+            return None;
-        .curve
+        }
-        .tessellate(DEFAULT_SEGMENTS_PER_RADIAN)
+        Some(projected)
-        .into_iter()
+    };
-        .map(|uv| {
+    let origin = glam::DVec2::from_array(map([0.0, 0.0])?);
-            let world = other.transform.apply(lift(&second.plane, uv));
+    let x = glam::DVec2::from_array(map([1.0, 0.0])?) - origin;
-            first.plane.project(dpoint(world)).unwrap_or(uv)
+    let y = glam::DVec2::from_array(map([0.0, 1.0])?) - origin;
-        })
+    let second = second.curve.transformed(&cadkernel::geom2d::Transform {
-        .collect::<Vec<_>>();
+        origin: origin.to_array().into(),
+        x_axis: x.to_array().into(),
+        y_axis: y.to_array().into(),
+    })?;
     let hint_uv = first.plane.project(dpoint(hint))?;
-    let mut best: Option<([f64; 2], f64)> = None;
+    let mut points: Vec<_> = cadkernel::geom2d::intersect(
-    for pair_a in a.windows(2) {
+        &first.curve,
-        for pair_b in b.windows(2) {
+        &second,
-            let Some(point) = segment_cross(pair_a[0], pair_a[1], pair_b[0], pair_b[1], false)
+        cadkernel::geom2d::Tolerance::new(1e-9),
-            else {
+    )
-                continue;
+    .into_iter()
-            };
+    .map(|hit| hit.point)
-            let error = (point[0] - hint_uv[0]).powi(2) + (point[1] - hint_uv[1]).powi(2);
+    .collect();
-            if best.is_none_or(|(_, previous)| error < previous) {
+    if apparent && points.is_empty() {
-                best = Some((point, error));
+        // Extended apparent intersections are meaningful for straight lines.
-            }
+        // Curved geometry must actually cross after projection.
+        if let (KernelCurve::Line(a), KernelCurve::Line(b)) = (&first.curve, &second) {
+            points.extend(segment_cross(a.start, a.end, b.start, b.end, true));
         }
     }
-    if best.is_none() && apparent {
+    points
-        // Nothing actually crosses: take the two segments nearest the stored
+        .into_iter()
-        // point and cross their infinite extensions.
+        .min_by(|a, b| {
-        let nearest = |run: &[[f64; 2]]| -> Option<([f64; 2], [f64; 2])> {
+            let error = |p: &[f64; 2]| (p[0] - hint_uv[0]).powi(2) + (p[1] - hint_uv[1]).powi(2);
-            run.windows(2)
+            error(a).total_cmp(&error(b))
-                .map(|pair| {
+        })
-                    let mid = [
+        .map(|point| lift(&first.plane, point))
-                        (pair[0][0] + pair[1][0]) * 0.5,
-                        (pair[0][1] + pair[1][1]) * 0.5,
-                    ];
-                    let error =
-                        (mid[0] - hint_uv[0]).powi(2) + (mid[1] - hint_uv[1]).powi(2);
-                    ((pair[0], pair[1]), error)
-                })
-                .min_by(|first, second| first.1.total_cmp(&second.1))
-                .map(|(pair, _)| pair)
-        };
-        let (a0, a1) = nearest(&a)?;
-        let (b0, b1) = nearest(&b)?;
-        best = segment_cross(a0, a1, b0, b1, true).map(|point| (point, 0.0));
-    }
-    best.map(|(point, _)| lift(&first.plane, point))
 }
 
 /// Crossing of segments `a0->a1` and `b0->b1`. With `extend` the parameters
@@ -633,3 +673,48 @@ fn segment_cross(
     }
     Some([a0[0] + d[0] * t, a0[1] + d[1] * t])
 }
+
+/// Internal markers are zero-based; imported edge markers are one-based.
+fn segment_index(reference: &AssocDimensionReference) -> Option<usize> {
+    let marker = if reference.main_subent_type == 2 {
+        reference.main_gs_marker.checked_sub(1)?
+    } else {
+        reference.main_gs_marker
+    };
+    usize::try_from(marker).ok()
+}
+
+fn imported_endpoint(
+    entity: &EntityType,
+    reference: &AssocDimensionReference,
+    hint: Option<Vector3>,
+) -> Option<Vector3> {
+    let planar = entity_curve(entity)?;
+    let t = match reference.osnap_distance {
+        v if v.abs() < 1e-9 => 0.0,
+        v if (v - 1.0).abs() < 1e-9 => 1.0,
+        _ => return None,
+    };
+    let point = match &planar.curve {
+        KernelCurve::Polyline(_) => {
+            let segment = segment_index(reference)?;
+            let point = lift(
+                &planar.plane,
+                planar.curve.segments().get(segment)?.point_at(t),
+            );
+            // Exporters can leave stale GS markers after editing a polyline.
+            // Beyond the unambiguous first-edge convention, require a real
+            // stored snap point to validate this imported endpoint. Zero and
+            // 2e50 sentinel points do not establish feature identity.
+            if segment > 0 && !hint.is_some_and(|hint| distance_squared(point, hint) < 1e-10) {
+                return None;
+            }
+            point
+        }
+        KernelCurve::Line(_) | KernelCurve::Arc(_) | KernelCurve::Nurbs(_) => {
+            lift(&planar.plane, planar.curve.point_at(t))
+        }
+        _ => return None,
+    };
+    Some(point)
+}

src/scene/entity.rs

@@ -134,7 +134,7 @@ impl Scene {
         let _ = self.document.layers.add(layer);
     }
 
-    fn ensure_app_id(&mut self, name: &str) {
+    pub(super) fn ensure_app_id(&mut self, name: &str) {
         if name.trim().is_empty() || self.document.app_ids.contains(name) {
             return;
         }

src/scene/viewport_dim_seam.rs

@@ -84,6 +84,9 @@ impl Scene {
                 continue;
             };
 
+            if !planar_pick_distance(&entity, model_point).is_some_and(|d| d <= aperture_model) {
+                continue;
+            }
             let mut paper_entity = entity;
             crate::scene::view::dispatch::apply_transform(
                 &mut paper_entity,
@@ -106,39 +109,6 @@ impl Scene {
         None
     }
 
-    /// Resolve a snapped INSERT handle into the innermost entity that owns the
-    /// geometry, plus the INSERT path down to it.
-    ///
-    /// The renderer names every wire of an expanded block with the **top-level
-    /// INSERT's** handle (see `block_cache`), including wires belonging to
-    /// nested inserts, so a snap inside a block reports the INSERT and nothing
-    /// finer. This walks the block definition from that INSERT looking for the
-    /// nearest measurable entity to `model_point`, which recovers the real
-    /// source handle and the instance path for the association chain.
-    ///
-    /// Returns `None` — and the caller then keeps the INSERT itself as the
-    /// source, which still gives a correct, if coarse, association — when:
-    /// * `top` is not an INSERT (the common case: `Some((top, vec![]))`);
-    /// * the geometry is a type [`planar_pick_distance`] does not handle
-    ///   (text, hatch, spline, solid, 3-D geometry);
-    /// * the nesting is deeper than eight levels.
-    ///
-    /// Depth is not limited to one level: [`Scene::descend_block_instance`]
-    /// recurses, and the returned path lists every INSERT from the outermost
-    /// down to the one that directly contains the entity.
-    pub fn resolve_block_snap_source(
-        &self,
-        top: Handle,
-        model_point: DVec3,
-    ) -> Option<(Handle, Vec<Handle>)> {
-        if !matches!(self.document.get_entity(top), Some(EntityType::Insert(_))) {
-            return None;
-        }
-        let (entity, path) = self.resolve_measurable_entity(top, model_point, None)?;
-        let handle = entity.as_entity().handle();
-        handle.is_valid().then_some((handle, path))
-    }
-
     /// Nearest resident model wire of `viewport` to `model_point`, within
     /// `aperture` model units. Wires are the same tessellation the viewport
     /// draws, so this matches what the user sees.
@@ -205,6 +175,16 @@ impl Scene {
         handle: Handle,
         model_point: DVec3,
         viewport: Option<Handle>,
+    ) -> Option<(EntityType, Vec<Handle>)> {
+        self.resolve_measurable_feature(handle, model_point, viewport, None)
+    }
+
+    pub(crate) fn resolve_measurable_feature(
+        &self,
+        handle: Handle,
+        model_point: DVec3,
+        viewport: Option<Handle>,
+        kind: Option<crate::snap::SnapType>,
     ) -> Option<(EntityType, Vec<Handle>)> {
         let entity = self.document.get_entity(handle)?;
         match entity {
@@ -217,11 +197,12 @@ impl Scene {
                     &mut path,
                     0,
                     viewport,
+                    kind,
                 )?;
                 Some((found.0, found.1))
             }
             other => {
-                planar_pick_distance(other, model_point)?;
+                feature_pick_distance(other, model_point, kind)?;
                 Some((other.clone(), Vec::new()))
             }
         }
@@ -237,6 +218,7 @@ impl Scene {
         path: &mut Vec<Handle>,
         depth: usize,
         viewport: Option<Handle>,
+        kind: Option<crate::snap::SnapType>,
     ) -> Option<(EntityType, Vec<Handle>)> {
         const MAX_DEPTH: usize = 8;
         if depth > MAX_DEPTH {
@@ -245,6 +227,9 @@ impl Scene {
         let EntityType::Insert(insert) = &insert_entity else {
             return None;
         };
+        if insert.row_count > 1 || insert.column_count > 1 {
+            return None;
+        }
         let insert_handle = insert.common.handle;
         let local = crate::scene::render_graph::insert_transform(&self.document, insert);
         let combined = local.then(&outer);
@@ -273,8 +258,9 @@ impl Scene {
                     &mut nested,
                     depth + 1,
                     viewport,
+                    kind,
                 ) {
-                    if let Some(distance) = planar_pick_distance(&entity, model_point) {
+                    if let Some(distance) = feature_pick_distance(&entity, model_point, kind) {
                         if best.as_ref().is_none_or(|(d, _, _)| distance < *d) {
                             let mut full = vec![insert_handle];
                             full.append(&mut nested_path);
@@ -294,6 +280,7 @@ impl Scene {
             let y = DVec3::new(m[0][1], m[1][1], m[2][1]);
             let magnitude = x.length_squared().max(y.length_squared());
             if curved
+                && kind != Some(crate::snap::SnapType::Center)
                 && (magnitude < 1e-24
                     || (x.length_squared() - y.length_squared()).abs() > magnitude * 1e-10
                     || x.dot(y).abs() > magnitude * 1e-10)
@@ -305,7 +292,7 @@ impl Scene {
                 &mut placed,
                 &EntityTransform::Affine(combined),
             );
-            let Some(distance) = planar_pick_distance(&placed, model_point) else {
+            let Some(distance) = feature_pick_distance(&placed, model_point, kind) else {
                 continue;
             };
             if best.as_ref().is_none_or(|(d, _, _)| distance < *d) {
@@ -438,3 +425,45 @@ mod tests {
         }
     }
 }
+
+/// Distance to the particular feature accepted by a snap, rather than to the
+/// nearest curve. A circle's center is deliberately not on its circumference.
+pub(crate) fn feature_pick_distance(
+    entity: &EntityType,
+    point: DVec3,
+    kind: Option<crate::snap::SnapType>,
+) -> Option<f64> {
+    use crate::snap::SnapType as S;
+    let points: Vec<acadrust::types::Vector3> = match kind {
+        Some(S::Center) => match entity {
+            EntityType::Circle(c) => vec![c.center_wcs()],
+            EntityType::Arc(a) => vec![a.center_wcs()],
+            EntityType::Ellipse(e) => vec![e.center],
+            _ => return None,
+        },
+        Some(S::Endpoint) => crate::scene::dimension_assoc::source_points(entity),
+        Some(S::Node) => match entity {
+            EntityType::Point(p) => vec![p.location],
+            _ => return None,
+        },
+        Some(S::Midpoint | S::Quadrant) => {
+            let planar = crate::entities::curve::entity_curve(entity)?;
+            cadkernel::geom2d::snap::characteristic_points(&planar.curve)
+                .into_iter()
+                .filter(|p| match kind {
+                    Some(S::Midpoint) => p.kind == cadkernel::geom2d::snap::SnapKind::Midpoint,
+                    _ => p.kind == cadkernel::geom2d::snap::SnapKind::Quadrant,
+                })
+                .map(|p| {
+                    let p = planar.plane.point_at(p.point);
+                    acadrust::types::Vector3::new(p[0], p[1], p[2])
+                })
+                .collect()
+        }
+        _ => return planar_pick_distance(entity, point),
+    };
+    points
+        .into_iter()
+        .map(|p| (DVec3::new(p.x, p.y, p.z) - point).truncate().length())
+        .min_by(f64::total_cmp)
+}

tests/fixtures/dim_assoc/README.md

@@ -0,0 +1,16 @@
+# Viewport association fixture
+
+`viewport_associations.dxf` is a synthetic paper-space fixture for line, circle,
+arc, polyline, spline, block-instance, and intersection references through one
+1:2 viewport. `src/app/viewport_dimension_tests.rs` loads it and exercises actual
+association refresh and an edit to the second intersection source.
+
+Each dimension carries `DIMLFAC=-2` and `ACAD_DIMASSOC_CALC_DIMLFAC=-2`. These are
+necessary for its paper definition points and saved model measurements to agree;
+the original fixture omitted both factors. The spline tangent also uses the
+actual touch point `(90, 283.125)` at parameter `0.75`, measured from `(0, 300)`.
+The original endpoint `(120, 300)` was not tangent. Tests verify the cross product
+with the spline derivative and preservation after an unsupported reference edit.
+
+The larger original `115448.dxf` is private and is not included. An opt-in test
+uses `OPENCAD_VIEWPORT_REGRESSION_DXF` to read a local copy without modifying it.

tests/fixtures/dim_assoc/viewport_associations.dxf

@@ -788,6 +788,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -844,6 +860,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -900,6 +932,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -956,6 +1004,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -991,7 +1055,7 @@ AcDbDimension
 71
 5
 42
-120.0
+91.56836585306085
 1
 
 3
@@ -1005,13 +1069,29 @@ AcDbAlignedDimension
 33
 0.0
 14
-135.0
+120.0
 24
-175.0
+166.5625
 34
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -1068,6 +1148,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 DIMENSION
 5
@@ -1124,6 +1220,22 @@ AcDbAlignedDimension
 0.0
 50
 0.0
+1001
+ACAD_DIMASSOC_CALC_DIMLFAC
+1040
+-2.0
+1001
+ACAD
+1000
+DSTYLE
+1002
+{
+1070
+144
+1040
+-2.0
+1002
+}
 0
 ENDSEC
 0
@@ -1475,11 +1587,11 @@ AcDbOsnapPointRef
 91
 -2
 40
-1.0
+0.75
 10
-120.0
+90.0
 20
-300.0
+283.125
 30
 0.0
 75