README.md

---
pretty_name: shapesplat
size_categories:
- 10K<n<100K
---

# 2D Image/Depth/Normal Rendering of ShapeNet

The image/depth/normal renders are in the [ShapeSplat_2d_renders](https://huggingface.co/datasets/ShapeSplats/sharing/tree/main/ShapeSplat_2d_renders) folder, and the camera parameters are saved in per-object `transforms.json` in the [ShapeSplat_render_cams](https://huggingface.co/datasets/ShapeSplats/sharing/tree/main/ShapeSplat_render_cams) folder. For 2D rendering, we save per-view frame information in the `transforms.json` for each object, in the format of:

```json
{
    "camera_angle_x": 0.6911112070083618,
    "frames": [
        {
            "file_path": "image/000",
            "rotation": 0.08726646259971647,
            "transform_matrix": [
                [
                    1.0, 0.0, 0.0, 0.0
                ],
                [
                    0.0, 0.5662031769752502, -0.8242656588554382, -1.0555751323699951
                ],
                [
                    0.0, 0.8242655992507935, 0.5662031769752502, 0.7250939011573792
                ],
                [
                    0.0, 0.0, 0.0, 1.0
                ]
            ]
        },
        { // ... more frames for this object
```

## Camera Intrinsics

The camera intrinsics are calculated from the `camera_angle_x` field in the transforms JSON file:

```python
def get_intrinsics(camera_angle_x: float, width: int = 400, height: int = 400):
    fx = width / (2 * np.tan(camera_angle_x / 2))
    fy = fx  # Square pixels assumed
    cx = width / 2.0   # Principal point at center
    cy = height / 2.0
    
    K = [[fx,  0, cx],
         [ 0, fy, cy], 
         [ 0,  0,  1]]
```

**Output:**
- Image dimensions: 400×400
- Camera FOV: 39.60°
- Intrinsics matrix:
  ```
  [[555.56    0   200  ]
   [  0   555.56 200  ]
   [  0     0     1   ]]
  ```

## Image Reading

**RGB Images:**
- Format: PNG files (000.png, 001.png, ...)
- Image in RGBA format (with alpha channel)
- Alpha channel cam be used for background masking

## Depth Reading

**Depth Maps:**
- Format: 4-channel RGBA PNG files from Blender ([frame_id]0001.png, e.g., 0000001.png, 0010001.png, ...)
- Note: Only the first channel (R) contains depth data
- Blender saves depth as inverted values: [0,8] meters → [1,0] normalized
- Script remaps back to linear depth: `depth_linear = depth_min + (1.0 - depth_img) * (depth_max - depth_min)`
- Background pixels have depth values close to 1.0 (far plane)

**Depth Reading:**
```python
# Extract first channel from 4-channel depth
depth_img = depth_img_raw[:, :, 0]

# Convert uint8 depth to float normalized to [0, 1]
depth_img = depth_img.astype(np.float32) / 255.0

# Note: Blender remaps [0, 8] to [1, 0]
# Remap depth values from [1, 0] back to [depth_min, depth_max]
depth_min, depth_max = 0, 8
depth_linear = depth_min + (1.0 - depth_img) * (depth_max - depth_min)

valid_mask = (depth_linear > 0.001) & (depth_linear < depth_max - 0.001)
background_mask = depth_img > 0.999

valid_mask = valid_mask & ~background_mask
```

# Coordinate Alignment to 3DGS and OBJ Mesh

Due to coordinate inconsistency at the beginning, the poses of the 2D renderings saved in `frame['transform_matrix']` is not aligned to the world coordinate of the 3DGS object and the OBJ mesh.

The following process are needed to convert the 'transform_matrix' key in order to align with the OBJ object mesh.
```
def convert_cam_coords(transform_matrix):
    P = np.array([
        [1, 0, 0, 0],
        [0, 0, 1, 0],
        [0, -1, 0, 0],
        [0, 0, 0, 1]
    ])

    C = np.array([
        [1,  0,  0, 0],
        [0, -1,  0, 0],
        [0,  0, -1, 0],
        [0,  0,  0, 1]
    ])

    new_transform_matrix = P @ transform_matrix @ C
    return new_transform_matrix

transform_matrix = np.array(frame['transform_matrix'])
transform_matrix = convert_cam_coords(transform_matrix)
```
After this process, the 2D rendering results will be aligned to the world coordinate as in the original shapenet object, i.e., point_cloud.obj file. For example, the fused depth maps with the processed poses with its point_cloud.obj together:

<img width="450" height="305" alt="Image" src="https://github.com/user-attachments/assets/ad210a02-420e-442a-a7b7-f54dd0b2b618" />

Additionally, there is misalignment between the released 3DGS object and the corresponding point_cloud.obj file.

To align the 2D rendering results with the released 3DGS, please use the following conversion instead:
```
# align to the 3dgs object coordinates
def convert_cam_coords(transform_matrix):
    C = np.array([
        [1,  0,  0, 0],
        [0, -1,  0, 0],
        [0,  0, -1, 0],
        [0,  0,  0, 1]
    ])

    new_transform_matrix = transform_matrix @ C
    return new_transform_matrix
```