docs: update Appearance_Feature_System with shot type detection

- Add reference units table (eye/head/shoulder width)
- Add BODY_PROPORTIONS constants for validation
- Add shot type detection section (full_body/medium_shot/close_up)
- Add height estimation strategies per shot type
- Update code examples with head_width and proportion_ratios

docs_v1.0/DESIGN/Appearance_Feature_System_V1.0.md

@@ -114,10 +114,73 @@ Face (identification) → Pose (tracking) → Appearance (tracking)
 
 ## Body Proportions Calculation
 
-### Reference Unit
+### Reference Units
+
+Multiple reference units for different shot types:
+
+| Unit | Real Size | Available In | Notes |
+|------|-----------|--------------|-------|
+| eye_width | ~6cm | Close-up | Most accurate in close-up |
+| head_width | ~16cm | Close-up to Medium | Ear-to-ear distance |
+| shoulder_width | ~45cm | Medium to Wide | Most stable reference |
+
 ```python
-# Eye distance as reference unit
-eye_width = distance(left_eye, right_eye)
+# Priority: shoulder_width > head_width > eye_width
+# Larger units more stable and available in wider shots
+```
+
+### Body Proportions Constants
+
+Standard adult body proportion ratios (used for validation and estimation):
+
+| Ratio | Value | Description |
+|-------|-------|-------------|
+| head_to_eye | 2.67 | head_width ≈ 2.67 × eye_width |
+| eye_to_shoulder | 7.5 | shoulder_width ≈ 7.5 × eye_width |
+| head_to_shoulder | 2.8 | shoulder_width ≈ 2.8 × head_width |
+| head_to_height | 7.5 | body_height ≈ 7.5 × head_width |
+| shoulder_to_height | 3.8 | body_height ≈ 3.8 × shoulder_width |
+
+### Shot Type Detection
+
+Detect shot type based on head position relative to bbox:
+
+| Shot Type | Head Position | Aspect Ratio | Description |
+|-----------|---------------|--------------|-------------|
+| full_body | < 15% from top | > 2.0 | Full person visible |
+| medium_shot | < 30% from top | > 1.5 | Upper body visible |
+| close_up | > 30% or middle | < 1.5 | Head/face dominant |
+
+```python
+# head_position_ratio = (head_y - bbox_top) / bbox_height
+# aspect_ratio = bbox_height / bbox_width
+
+if head_position_ratio < 0.15 and aspect_ratio > 2.0:
+    shot_type = "full_body"
+elif head_position_ratio < 0.30 and aspect_ratio > 1.5:
+    shot_type = "medium_shot"
+else:
+    shot_type = "close_up"
+```
+
+**Usage**: Filter frames by shot type (e.g., find all full-body shots in video).
+
+### Height Estimation
+
+Height estimation strategy based on shot type:
+
+| Shot Type | Method | Formula | Result |
+|-----------|--------|---------|--------|
+| full_body | Direct measurement | body_height / ref_unit × ref_cm | Accurate |
+| medium_shot | Torso extrapolate | torso × (1/0.45) | ~170cm |
+| close_up | Proportion estimate | shoulder × 3.8 | ~171cm |
+
+```python
+# Close-up: use shoulder_width × 3.8
+estimated_height_cm = 45.0 * 3.8  # ≈ 171cm
+
+# Or use head_width × 7.5
+estimated_height_cm = 16.0 * 7.5  # ≈ 120cm (lower confidence)
 ```
 
 ### Body Measurements
@@ -137,59 +200,56 @@ leg_height = ankle_y - hip_y
 
 # Shoulder width
 shoulder_width = distance(left_shoulder, right_shoulder)
+
+# Head width (ear to ear)
+head_width = distance(left_ear, right_ear)
 ```
 
 ### Proportion Ratios
 ```python
 proportions = {
+    'shot_type': detect_shot_type(keypoints, bbox),
     'eye_width': eye_width,
+    'head_width': head_width,
     'body_height': body_height,
     'torso_height': torso_height,
     'leg_height': leg_height,
     'shoulder_width': shoulder_width,
-    'head_ratio': eye_width / body_height,
-    'torso_ratio': torso_height / body_height,
-    'leg_ratio': leg_height / body_height,
+    'head_ratio': eye_width / body_height if body_height > 0 else 0,
+    'torso_ratio': torso_height / body_height if body_height > 0 else 0,
+    'leg_ratio': leg_height / body_height if body_height > 0 else 0,
+}
+
+# Validation ratios (should match BODY_PROPORTIONS constants)
+proportion_ratios = {
+    'head_to_eye': head_width / eye_width if eye_width > 0 else 0,      # ~2.67
+    'shoulder_to_head': shoulder_width / head_width if head_width > 0 else 0,  # ~2.8
+    'shoulder_to_eye': shoulder_width / eye_width if eye_width > 0 else 0,    # ~7.5
 }
 ```
 
-### Body Shape Calculation (三圍)
+### Body Shape Classification
+
+Classification based on chest/waist/hip ratios:
+
+| Shape | Criteria | Description |
+|-------|----------|-------------|
+| hourglass | chest_waist < 1.0, waist_hip < 0.9 | Balanced proportions |
+| triangle | chest_waist > 1.2 | Upper body dominant |
+| inverted_triangle | waist_hip > 1.1 | Lower body dominant |
+| rectangle | chest ≈ hip | Uniform width |
+| oval | Other | General classification |
+
 ```python
-# Chest width (shoulder width approximation)
+# Measurements
 chest_width = distance(left_shoulder, right_shoulder)
-
-# Waist width (hip width approximation)
 waist_width = distance(left_hip, right_hip)
-
-# Hip width
 hip_width = distance(left_hip, right_hip)
 
-# Body shape classification
-if chest_waist_ratio < 1.0 and waist_hip_ratio < 0.9:
-    shape_type = "hourglass"  #葫芦形
-elif chest_waist_ratio > 1.2:
-    shape_type = "triangle"  # 倒三角
-elif waist_hip_ratio > 1.1:
-    shape_type = "inverted_triangle"  # 正三角
-elif abs(chest_width - hip_width) < 0.1 * max(chest_width, hip_width):
-    shape_type = "rectangle"  #矩形
-else:
-    shape_type = "oval"  #椭圆形
+# Ratios
+chest_waist_ratio = chest_width / waist_width
+waist_hip_ratio = waist_width / hip_width
 ```
-
-### Height Estimation
-```python
-# Use eye_width as reference (≈6cm)
-height_ratio = body_height / eye_width
-estimated_height_cm = height_ratio * 6.0
-
-# Height category
-if estimated_height_cm < 150:
-    height_category = "short"
-elif estimated_height_cm < 170:
-    height_category = "medium"
-elif estimated_height_cm < 180:
-    height_category = "tall"
 else:
     height_category = "very_tall"
 ```