Update README.md

README.md

@@ -70,24 +70,106 @@ These categories can be used for dataset balancing, conditional models, or evalu
 
 ## Data Format
 
-Each sample is stored as a single JSON file:
-
+### Root Structure
+The JSON file has two main top-level objects:
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `metadata` | object | Contains general information about the export |
+| `bones` | object | Dictionary of bone objects keyed by bone names |
+
+### Metadata Object
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `armature_name` | string | Name of the armature (e.g., "KIM_caucasian_male") |
+| `export_time` | string | ISO 8601 timestamp of export |
+| `blender_version` | string | Version of Blender used for export |
+| `bone_count` | integer | Total number of bones in the armature |
+| `end_bone_count` | integer | Number of end bones (bones without children) |
+| `spaces_included` | array[string] | List of coordinate spaces included in the export |
+| `note` | string | Usage note (e.g., replay instructions) |
+
+### Bones Object
+The `bones` object contains a dictionary where keys are bone names and values are bone objects.
+
+#### Bone Object Structure
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `name` | string | Name of the bone (duplicates the dictionary key) |
+| `local` | object | Transform data in bone's local space |
+| `armature_space` | object | Transform data in armature space |
+| `world_space` | object | Transform data in world space |
+| `bone_length_armature_space` | float | Length of the bone in armature space |
+| `parent` | string or null | Name of parent bone (null for root) |
+| `has_children` | boolean | Whether this bone has child bones |
+| `is_end_bone` | boolean | Whether this bone is an end bone (no children) |
+
+#### Local Transform Object
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `location` | object | Translation vector as `{x, y, z}` |
+| `rotation_quaternion` | object | Rotation as quaternion `{w, x, y, z}` |
+| `scale` | object | Scale vector as `{x, y, z}` |
+| `matrix_basis` | 4x4 array | 4x4 transformation matrix for pose |
+| `rotation_mode` | string | Rotation representation method (always "QUATERNION") |
+
+#### Armature Space Object
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `head` | object | Start point of bone as `{x, y, z}` |
+| `tail` | object | End point of bone as `{x, y, z}` |
+
+#### World Space Object
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `head` | object | Start point in world coordinates `{x, y, z}` |
+| `tail` | object | End point in world coordinates `{x, y, z}` |
+| `rotation_quaternion` | object | World rotation as quaternion `{w, x, y, z}` |
+| `matrix` | 4x4 array | Complete 4x4 world transformation matrix |
+
+### Coordinate Spaces Explanation
+
+1. **LOCAL_CHANNELS**: Bone transformations relative to its rest pose (as shown in Blender's Transform panel)
+2. **ARMATURE_SPACE**: Bone positions relative to armature origin
+3. **WORLD_SPACE**: Bone positions in global scene coordinates
+
+### Important Notes
+
+- The `local.matrix_basis` field contains the exact pose transformation and should be used for precise pose replication
+- Quaternion format uses `w` as the scalar component and `(x, y, z)` as the vector components
+- All transformation matrices are 4x4 and stored in row-major order
+- The `spaces_included` array indicates which coordinate spaces are available in the export
+
+### Example Bone Entry
 ```json
-{
-  "pose_3d": {
-    "format": "coco_wholebody_133",
-    "joints": [[x, y, z], ...]
+"Root": {
+  "name": "Root",
+  "local": {
+    "location": {"x": 0.0, "y": 0.0, "z": 0.0},
+    "rotation_quaternion": {"w": 0.9998, "x": 0.0068, "y": -0.0153, "z": -0.0092},
+    "scale": {"x": 1.0, "y": 1.0, "z": 1.0},
+    "matrix_basis": [[...4x4 matrix...]],
+    "rotation_mode": "QUATERNION"
+  },
+  "armature_space": {
+    "head": {"x": 0.0, "y": 0.0707, "z": -0.0096},
+    "tail": {"x": 0.0013, "y": -0.0001, "z": -0.0010}
   },
-  "avatar_pose": {
-    "representation": "quaternion",
-    "joints": [[x, y, z, w], ...]
+  "world_space": {
+    "head": {"x": 0.0, "y": 0.1340, "z": 0.9403},
+    "tail": {"x": 0.0013, "y": 0.0631, "z": 0.9489},
+    "rotation_quaternion": {"w": 0.0606, "x": 0.9980, "y": 0.0082, "z": -0.0159},
+    "matrix": [[...4x4 world matrix...]]
   },
-  "metadata": {
-    "category": "open_hand",
-    "source": "synthetic_blender",
-    "coordinate_system": "right-handed",
-    "unit": "meters"
-  }
+  "bone_length_armature_space": 0.0714,
+  "parent": null,
+  "has_children": true,
+  "is_end_bone": false
 }
 ```