{
  "coordinate_system": {
    "origin": "B",
    "x_axis_direction": "B→A",
    "unit_scale": "BC=4.5cm → 4.5"
  },
  "elements": {
    "points": [
      {"name": "A", "role": "vertex", "estimated_coord": [3.2, 0]},
      {"name": "B", "role": "vertex", "estimated_coord": [0, 0]},
      {"name": "C", "role": "vertex", "estimated_coord": [0, 4.5]},
      {"name": "G", "role": "centroid", "estimated_coord": [1.6, 1.5]},
      {"name": "P", "role": "orthocenter", "estimated_coord": [1.8, 2.7]},
      {"name": "Q", "role": "circumcenter", "estimated_coord": [1.6, 2.25]},
      {"name": "R", "role": "incenter", "estimated_coord": [1.2, 1.8]}
    ],
    "lines": [
      {"type": "segment", "points": ["A", "B"], "properties": ["base_line"]},
      {"type": "segment", "points": ["B", "C"], "properties": ["vertical"]},
      {"type": "segment", "points": ["A", "C"], "properties": ["hypotenuse"]},
      {"type": "ray", "points": ["B", "G"], "direction": "B→G"},
      {"type": "ray", "points": ["A", "P"], "direction": "A→P"}
    ],
    "circles": [
      {"center": "Q", "radius_point": "B", "properties": ["dashed"]},
      {"center": "R", "radius_point": "D", "properties": ["solid"]}
    ],
    "polygons": [
      {"vertices": ["A","B","C"], "type": "triangle", "properties": ["right_angled_at_B"]}
    ]
  },
  "spatial_relations": [
    "AB ⊥ BC (直角符号)",
    "点G ∈ 中线BG",
    "点P ∈ 高线AP",
    "圆Q 外切 △ABC",
    "圆R 内切 △ABC",
    "AG:GD = 2:1 (重心性质)"
  ],
  "annotations": {
    "explicit": [
      {"type": "length", "element": "BC", "value": 4.5, "unit": "cm"},
      {"type": "angle", "element": "∠ABC", "value": 90, "unit": "degree"}
    ],
    "implicit": [
      "由重心性质得 BG:GG' = 2:1",
      "由垂心性质得 AP⊥BC"
    ]
  },
  "confidence_notes": [
    "点D位置未标注→估算为BC中点",
    "圆R半径未标注→基于内切圆公式计算"
  ]
}