model/data_augmentation.py

# ================================
# Point Cloud Augmentation Functions (Single + Batched)
# ================================

import torch
import math


# -------------------------------
# Center the point cloud
# -------------------------------
def center_point_cloud(points: torch.Tensor):
    """
    Center a point cloud by subtracting its centroid.

    Args:
        points:
            (N, 3) or (B, N, 3) tensor

    Returns:
        centered_points:
            same shape as input
        center:
            (1, 3) if input was (N, 3)
            (B, 1, 3) if input was (B, N, 3)
    """
    assert points.dim() in (2, 3) and points.size(-1) == 3, \
        "Expected shape (N,3) or (B,N,3)"

    if points.dim() == 2:
        # (N,3)
        center = points.mean(dim=0, keepdim=True)      # (1,3)
        centered = points - center                     # (N,3)
    else:
        # (B,N,3)
        center = points.mean(dim=1, keepdim=True)      # (B,1,3)
        centered = points - center                     # (B,N,3)

    return centered, center


# -------------------------------
# Random rotation helpers
# -------------------------------
def random_rotation_matrix(
    batch_size: int | None = None,
    device=None,
    dtype=torch.float32,
):
    """
    Generate random 3D rotation matrix/matrices.

    If batch_size is None:
        returns (3, 3) rotation matrix.
    Else:
        returns (B, 3, 3) rotation matrices.

    Uniform sampling over SO(3) using independent yaw-pitch-roll.
    (Not perfectly uniform on SO(3) but good enough for augmentation.)
    """
    if device is None:
        device = torch.device("cpu")

    if batch_size is None:
        angles = torch.rand(3, device=device, dtype=dtype) * 2 * math.pi  # (3,)
        cx, cy, cz = torch.cos(angles)
        sx, sy, sz = torch.sin(angles)

        rot_x = torch.tensor([
            [1,   0,   0],
            [0,  cx, -sx],
            [0,  sx,  cx],
        ], device=device, dtype=dtype)

        rot_y = torch.tensor([
            [ cy, 0, sy],
            [  0, 1,  0],
            [-sy, 0, cy],
        ], device=device, dtype=dtype)

        rot_z = torch.tensor([
            [cz, -sz, 0],
            [sz,  cz, 0],
            [ 0,   0, 1],
        ], device=device, dtype=dtype)

        R = rot_z @ rot_y @ rot_x  # (3,3)
        return R

    else:
        # batch of rotations
        angles = torch.rand(batch_size, 3, device=device, dtype=dtype) * 2 * math.pi  # (B,3)
        cx, cy, cz = torch.cos(angles[:, 0]), torch.cos(angles[:, 1]), torch.cos(angles[:, 2])
        sx, sy, sz = torch.sin(angles[:, 0]), torch.sin(angles[:, 1]), torch.sin(angles[:, 2])

        # build batched rotation matrices
        R = torch.zeros(batch_size, 3, 3, device=device, dtype=dtype)

        # RotX
        R_x = torch.zeros_like(R)
        R_x[:, 0, 0] = 1
        R_x[:, 1, 1] = cx
        R_x[:, 1, 2] = -sx
        R_x[:, 2, 1] = sx
        R_x[:, 2, 2] = cx

        # RotY
        R_y = torch.zeros_like(R)
        R_y[:, 0, 0] = cy
        R_y[:, 0, 2] = sy
        R_y[:, 1, 1] = 1
        R_y[:, 2, 0] = -sy
        R_y[:, 2, 2] = cy

        # RotZ
        R_z = torch.zeros_like(R)
        R_z[:, 0, 0] = cz
        R_z[:, 0, 1] = -sz
        R_z[:, 1, 0] = sz
        R_z[:, 1, 1] = cz
        R_z[:, 2, 2] = 1

        # Z * Y * X, batched
        # (B,3,3) @ (B,3,3) -> (B,3,3)
        R = torch.bmm(R_z, torch.bmm(R_y, R_x))
        return R


# -------------------------------
# Full 3D rotation
# -------------------------------
def rotate_point_cloud(points: torch.Tensor, R: torch.Tensor = None):
    """
    Rotate a point cloud with optional rotation matrix.

    Args:
        points:
            (N,3) or (B,N,3)
        R:
            If points is (N,3):
                None or (3,3)
            If points is (B,N,3):
                None, (3,3) shared, or (B,3,3) per-cloud.

    Returns:
        rotated_points: same shape as points
        R: (3,3) or (B,3,3) rotation used
    """
    assert points.dim() in (2, 3) and points.size(-1) == 3, \
        "Expected shape (N,3) or (B,N,3)"

    device, dtype = points.device, points.dtype

    if points.dim() == 2:
        # (N,3)
        if R is None:
            R = random_rotation_matrix(device=device, dtype=dtype)  # (3,3)
        assert R.shape == (3, 3), "R must be (3,3) for single cloud"
        rotated = points @ R.T  # (N,3)
        return rotated, R

    else:
        # (B,N,3)
        B, N, _ = points.shape

        if R is None:
            R = random_rotation_matrix(batch_size=B, device=device, dtype=dtype)  # (B,3,3)
        elif R.dim() == 2:
            # broadcast shared rotation to all clouds
            assert R.shape == (3, 3), "R must be (3,3) or (B,3,3)"
            R = R.unsqueeze(0).expand(B, -1, -1)  # (B,3,3)
        else:
            assert R.shape == (B, 3, 3), "R must be (3,3) or (B,3,3)"

        # rotated[b, n, :] = points[b, n, :] @ R[b].T
        rotated = torch.einsum("bnc,bfc->bnf", points, R.transpose(1, 2))  # (B,N,3)
        return rotated, R


# -------------------------------
# Rotation around z-axis only
# -------------------------------
def rotate_point_cloud_z(points: torch.Tensor, angle=None):
    """
    Rotate point cloud around z-axis only.

    Args:
        points:
            (N,3) or (B,N,3)
        angle:
            If points is (N,3): float or None (radians).
                - None: sample random in [0, 2π).
            If points is (B,N,3): tensor of shape (B,) or None.
                - None: random angle per cloud in [0, 2π).

    Returns:
        rotated_points: same shape as points
        Rz:
            (3,3) for single cloud
            (B,3,3) for batched
    """
    assert points.dim() in (2, 3) and points.size(-1) == 3, \
        "Expected shape (N,3) or (B,N,3)"

    device, dtype = points.device, points.dtype

    if points.dim() == 2:
        # single cloud (N,3)
        if angle is None:
            angle = torch.rand(1, device=device, dtype=dtype).item() * 2 * math.pi
        c, s = math.cos(angle), math.sin(angle)
        Rz = torch.tensor([
            [c, -s, 0],
            [s,  c, 0],
            [0,  0, 1],
        ], device=device, dtype=dtype)
        rotated = points @ Rz.T  # (N,3)
        return rotated, Rz

    else:
        # batched (B,N,3)
        B, N, _ = points.shape
        if angle is None:
            angle = torch.rand(B, device=device, dtype=dtype) * 2 * math.pi  # (B,)
        elif not torch.is_tensor(angle):
            # scalar -> shared angle
            angle = torch.full((B,), float(angle), device=device, dtype=dtype)

        c = torch.cos(angle)  # (B,)
        s = torch.sin(angle)  # (B,)

        Rz = torch.zeros(B, 3, 3, device=device, dtype=dtype)
        Rz[:, 0, 0] = c
        Rz[:, 0, 1] = -s
        Rz[:, 1, 0] = s
        Rz[:, 1, 1] = c
        Rz[:, 2, 2] = 1

        rotated = torch.einsum("bnc,bfc->bnf", points, Rz.transpose(1, 2))  # (B,N,3)
        return rotated, Rz


# -------------------------------
# Translation
# -------------------------------
def translate_point_cloud(points: torch.Tensor,
                          t: torch.Tensor = None,
                          scale: float = 0.05):
    """
    Translate a point cloud.

    Args:
        points:
            (N,3) or (B,N,3)
        t:
            Translation vector.
            For (N,3): None, (3,), or (1,3).
            For (B,N,3): None, (3,), (1,3), or (B,3).
        scale:
            Magnitude for random translation when t is None.

    Returns:
        translated_points: same shape as points
        t_out:
            (1,3) for single cloud
            (B,1,3) for batched clouds
    """
    assert points.dim() in (2, 3) and points.size(-1) == 3, \
        "Expected shape (N,3) or (B,N,3)"

    device, dtype = points.device, points.dtype

    if points.dim() == 2:
        # (N,3)
        if t is None:
            t = (torch.rand(1, 3, device=device, dtype=dtype) * 2 - 1) * scale  # (1,3)
        t = t.view(1, 3)
        translated = points + t  # (N,3)
        return translated, t

    else:
        # (B,N,3)
        B, N, _ = points.shape
        if t is None:
            t = (torch.rand(B, 3, device=device, dtype=dtype) * 2 - 1) * scale  # (B,3)
        else:
            if t.dim() == 1:
                assert t.shape[0] == 3, "t must be (3,), (1,3), or (B,3)"
                t = t.view(1, 3).expand(B, -1)    # (B,3)
            elif t.dim() == 2:
                if t.shape[0] == 1:
                    # (1,3) -> broadcast
                    t = t.expand(B, -1)           # (B,3)
                else:
                    assert t.shape == (B, 3), "t must be (3,), (1,3), or (B,3)"
            else:
                raise ValueError("t must have shape (3,), (1,3), or (B,3)")

        t_out = t.view(B, 1, 3)                   # (B,1,3)
        translated = points + t_out               # (B,N,3)
        return translated, t_out


# -------------------------------
# Scaling
# -------------------------------
def scale_point_cloud(points: torch.Tensor,
                      s: torch.Tensor = None,
                      min_s: float = 0.9,
                      max_s: float = 1.1):
    """
    Uniformly scale a point cloud.

    Args:
        points:
            (N,3) or (B,N,3)
        s:
            If points is (N,3):
                None or scalar tensor (or shape (1,))
            If points is (B,N,3):
                None, scalar, or (B,) for per-cloud scaling.
        min_s, max_s:
            Range for random scaling when s is None.

    Returns:
        scaled_points: same shape as points
        s_vec:
            (1,3) if single cloud
            (B,1,3) if batched
    """
    assert points.dim() in (2, 3) and points.size(-1) == 3, \
        "Expected shape (N,3) or (B,N,3)"

    device, dtype = points.device, points.dtype

    if points.dim() == 2:
        # (N,3)
        if s is None:
            s = torch.empty(1, device=device, dtype=dtype).uniform_(min_s, max_s)  # (1,)
        if torch.is_tensor(s):
            s = s.view(1, 1)  # scalar
        else:
            s = torch.tensor([[float(s)]], device=device, dtype=dtype)
        s_vec = s.repeat(1, 3)       # (1,3)
        scaled = points * s          # (N,3)
        return scaled, s_vec

    else:
        # (B,N,3)
        B, N, _ = points.shape
        if s is None:
            s = torch.empty(B, device=device, dtype=dtype).uniform_(min_s, max_s)  # (B,)
        elif not torch.is_tensor(s):
            s = torch.full((B,), float(s), device=device, dtype=dtype)

        assert s.shape == (B,), "For batched input, s must be scalar or shape (B,)"

        s = s.view(B, 1, 1)          # (B,1,1)
        s_vec = s.repeat(1, 1, 3)    # (B,1,3)
        scaled = points * s          # (B,N,3)
        return scaled, s_vec


# -------------------------------
# Example: Full augmentation pipeline
# -------------------------------
def augment_point_cloud(points: torch.Tensor):
    """
    Example augmentation pipeline:
    center -> random rotate -> random scale -> random translate

    Works for:
        (N,3)  or (B,N,3)

    Returns:
        aug_points: same shape as input
        info: dict with keys center, R, s, t
            center: (1,3) or (B,1,3)
            R:      (3,3) or (B,3,3)
            s:      (1,3) or (B,1,3)
            t:      (1,3) or (B,1,3)
    """
    pts, center = center_point_cloud(points)
    pts, R = rotate_point_cloud(pts)
    pts, s = scale_point_cloud(pts, min_s=0.8, max_s=1.2)
    pts, t = translate_point_cloud(pts, scale=0.1)

    info = dict(center=center, R=R, s=s, t=t)
    return pts, info