{
  "coordinate_system": {
    "origin": "A",
    "x_axis_direction": "A→B",
    "unit_scale": "AB=10 units (estimated)"
  },
  "elements": {
    "points": [
      {"name": "A", "role": "vertex", "estimated_coord": [0, 0]},
      {"name": "B", "role": "vertex", "estimated_coord": [10, 0]},
      {"name": "C", "role": "vertex", "estimated_coord": [5, 8]},
      {"name": "D", "role": "midpoint", "estimated_coord": [2, 0], "properties": ["on_AB"]},
      {"name": "E", "role": "midpoint", "estimated_coord": [8, 0], "properties": ["on_AB"]},
      {"name": "F", "role": "intersection", "estimated_coord": [7, 4], "properties": ["on_BC"]}
    ],
    "lines": [
      {"type": "segment", "points": ["A", "B"], "properties": ["base_line"]},
      {"type": "segment", "points": ["A", "C"], "properties": ["median"]},
      {"type": "segment", "points": ["B", "C"], "properties": ["side"]},
      {"type": "ray", "points": ["C", "F"], "direction": "C→F"}
    ],
    "polygons": [
      {"vertices": ["A","B","C"], "type": "triangle", "properties": ["scalene"]}
    ]
  },
  "spatial_relations": [
    "AB ⊥ CF (visual alignment)",
    "点D ∈ 线段AB",
    "点E ∈ 线段AB",
    "点F ∈ 线段BC",
    "AD ≈ BE (length estimation)"
  ],
  "annotations": {
    "explicit": [],
    "implicit": [
      "由中点符号得 AD=BD",
      "由交点位置得 F为BC三等分点"
    ]
  },
  "confidence_notes": [
    "点F位置依赖于BC分割比例→低精度",
    "垂直关系需测量验证"
  ]
}