{
 "id": "82-thin-extrude-frame",
 "name": "Thin extrude frame",
 "description": "40x40 square of lines centred on origin; a thin wall 3 mm inside and 1 mm outside the lines, extruded 10 mm.",
 "exercises": [
  "extrude",
  "thin"
 ],
 "units": {
  "length": "mm",
  "angle": "deg",
  "area": "mm2",
  "volume": "mm3"
 },
 "conventions": {
  "world": "right-handed; Z up. XY/XZ/YZ are the origin planes.",
  "sketch_frame": "sketch-local 2D coords; world = plane.origin + x*plane.x_dir + y*plane.y_dir (origin in mm). Profile 'loops' list sketch entity ids.",
  "point_refs": "'<id>.start' / '<id>.end' / '<id>.center' reuse (share) that existing sketch point; 'at' is its position when referenced.",
  "extrude_direction": "positive = along sketch plane normal unless stated",
  "selections": "selected faces/edges carry 'point': a world-space point on the face / the edge's parametric midpoint; pick the nearest face/edge to it."
 },
 "parameters": [],
 "features": [
  {
   "op": "sketch",
   "name": "Sketch1",
   "plane": {
    "ref": "XY",
    "origin": [
     0.0,
     0.0,
     0.0
    ],
    "x_dir": [
     1.0,
     0.0,
     0.0
    ],
    "y_dir": [
     0.0,
     1.0,
     0.0
    ],
    "normal": [
     0.0,
     0.0,
     1.0
    ]
   },
   "entities": [
    {
     "type": "line",
     "start": {
      "at": [
       -20,
       -20
      ]
     },
     "end": {
      "at": [
       20,
       -20
      ]
     },
     "id": "l1"
    },
    {
     "type": "line",
     "start": {
      "ref": "l1.end",
      "at": [
       20.0,
       -20.0
      ]
     },
     "end": {
      "at": [
       20,
       20
      ]
     },
     "id": "l2"
    },
    {
     "type": "line",
     "start": {
      "ref": "l2.end",
      "at": [
       20.0,
       20.0
      ]
     },
     "end": {
      "at": [
       -20,
       20
      ]
     },
     "id": "l3"
    },
    {
     "type": "line",
     "start": {
      "ref": "l3.end",
      "at": [
       -20.0,
       20.0
      ]
     },
     "end": {
      "ref": "l1.start",
      "at": [
       -20.0,
       -20.0
      ]
     },
     "id": "l4"
    }
   ],
   "constraints": [],
   "dimensions": []
  },
  {
   "op": "extrude",
   "name": "Frame",
   "operation": "new",
   "extent": {
    "type": "distance",
    "distance": 10,
    "direction": "positive"
   },
   "result_bodies": [
    "Frame"
   ],
   "thin": {
    "sketch": "Sketch1",
    "curves": [
     "l1",
     "l2",
     "l3",
     "l4"
    ],
    "thickness": 3,
    "side": "two_sides",
    "thickness2": 1
   }
  }
 ]
}