{
 "id": "64-sketch-tangent-arc-chain",
 "name": "Sketch solver: tangent arc chain",
 "description": "Four alternating 3-point arcs (wave) closed by three lines; equal/tangent/horizontal-points constraints, R12, chord 20, line 20; solved then extruded 3.",
 "exercises": [
  "sketch_only",
  "sketch_constraints",
  "tangent",
  "equal",
  "arc_chain"
 ],
 "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": "Wave",
   "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": "arc_three_point",
     "start": {
      "at": [
       20,
       0.5
      ]
     },
     "mid": [
      10,
      5.5
     ],
     "end": {
      "at": [
       0.5,
       -0.5
      ]
     },
     "id": "a1"
    },
    {
     "type": "arc_three_point",
     "start": {
      "ref": "a1.start",
      "at": [
       20.0,
       0.5
      ]
     },
     "mid": [
      30,
      -4.5
     ],
     "end": {
      "at": [
       40,
       0.5
      ]
     },
     "id": "a2"
    },
    {
     "type": "arc_three_point",
     "start": {
      "at": [
       60,
       -0.5
      ]
     },
     "mid": [
      50,
      5
     ],
     "end": {
      "at": [
       40.5,
       0.5
      ]
     },
     "id": "a3"
    },
    {
     "type": "arc_three_point",
     "start": {
      "ref": "a3.start",
      "at": [
       60.0,
       -0.5
      ]
     },
     "mid": [
      70,
      -5
     ],
     "end": {
      "at": [
       79,
       0.5
      ]
     },
     "id": "a4"
    },
    {
     "type": "line",
     "start": {
      "ref": "a4.end",
      "at": [
       79.0,
       0.5
      ]
     },
     "end": {
      "at": [
       80,
       -19
      ]
     },
     "id": "l1"
    },
    {
     "type": "line",
     "start": {
      "ref": "l1.end",
      "at": [
       80.0,
       -19.0
      ]
     },
     "end": {
      "at": [
       1,
       -21
      ]
     },
     "id": "l2"
    },
    {
     "type": "line",
     "start": {
      "ref": "l2.end",
      "at": [
       1.0,
       -21.0
      ]
     },
     "end": {
      "ref": "a1.end",
      "at": [
       0.5,
       -0.5
      ]
     },
     "id": "l3"
    }
   ],
   "constraints": [
    {
     "type": "coincident",
     "refs": [
      "a1.end",
      "origin"
     ]
    },
    {
     "type": "horizontal_points",
     "refs": [
      "a1.start",
      "a1.end"
     ]
    },
    {
     "type": "coincident",
     "refs": [
      "a3.end",
      "a2.end"
     ]
    },
    {
     "type": "equal",
     "refs": [
      "a1",
      "a2"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "a1",
      "a2"
     ]
    },
    {
     "type": "equal",
     "refs": [
      "a2",
      "a3"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "a2",
      "a3"
     ]
    },
    {
     "type": "equal",
     "refs": [
      "a3",
      "a4"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "a3",
      "a4"
     ]
    },
    {
     "type": "horizontal_points",
     "refs": [
      "a2.start",
      "a2.end"
     ]
    },
    {
     "type": "horizontal_points",
     "refs": [
      "a3.start",
      "a3.end"
     ]
    },
    {
     "type": "horizontal_points",
     "refs": [
      "a4.start",
      "a4.end"
     ]
    },
    {
     "type": "vertical",
     "refs": [
      "l1"
     ]
    },
    {
     "type": "horizontal",
     "refs": [
      "l2"
     ]
    },
    {
     "type": "vertical",
     "refs": [
      "l3"
     ]
    }
   ],
   "dimensions": [
    {
     "type": "radius",
     "refs": [
      "a1"
     ],
     "value": 12,
     "unit": "mm"
    },
    {
     "type": "distance",
     "refs": [
      "a1.end",
      "a1.start"
     ],
     "value": 20,
     "unit": "mm",
     "orientation": "horizontal"
    },
    {
     "type": "distance",
     "refs": [
      "l1.start",
      "l1.end"
     ],
     "value": 20,
     "unit": "mm",
     "orientation": "vertical"
    }
   ]
  },
  {
   "op": "extrude",
   "name": "Extrude1",
   "operation": "new",
   "profiles": [
    {
     "sketch": "Wave",
     "loops": [
      {
       "outer": true,
       "curves": [
        "a1",
        "a2",
        "a3",
        "a4",
        "l1",
        "l2",
        "l3"
       ]
      }
     ]
    }
   ],
   "extent": {
    "type": "distance",
    "distance": 3,
    "direction": "positive"
   },
   "result_bodies": [
    "Wave"
   ]
  }
 ]
}