vggt/utils/pose_enc.py

# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.

import torch
from .rotation import quat_to_mat, mat_to_quat


def extri_intri_to_pose_encoding(
    extrinsics,
    intrinsics,
    image_size_hw=None,  # e.g., (256, 512)
    pose_encoding_type="absT_quaR_FoV",
    min_focal_length=0.1,
    max_focal_length=10,
):

    # extrinsics: BxSx3x4
    # intrinsics: BxSx3x3

    if pose_encoding_type == "absT_quaR_FoV":
        R = extrinsics[:, :, :3, :3]  # BxSx3x3
        T = extrinsics[:, :, :3, 3]  # BxSx3

        quat = mat_to_quat(R)
        # R_reverse = quat_to_mat(quat)
        # Note the order of h and w here
        H, W = image_size_hw
        fov_h = 2 * torch.atan((H / 2) / intrinsics[..., 1, 1])
        fov_w = 2 * torch.atan((W / 2) / intrinsics[..., 0, 0])
        pose_encoding = torch.cat([T, quat, fov_h[..., None], fov_w[..., None]], dim=-1).float()
    else:
        raise NotImplementedError

    return pose_encoding


def pose_encoding_to_extri_intri(
    pose_encoding,
    image_size_hw=None,  # e.g., (256, 512)
    min_focal_length=0.1,
    max_focal_length=10,
    pose_encoding_type="absT_quaR_FoV",
    build_intrinsics=True,
):

    intrinsics = None

    if pose_encoding_type == "absT_quaR_FoV":
        T = pose_encoding[..., :3]
        quat = pose_encoding[..., 3:7]
        fov_h = pose_encoding[..., 7]
        fov_w = pose_encoding[..., 8]

        R = quat_to_mat(quat)
        extrinsics = torch.cat([R, T[..., None]], dim=-1)

        if build_intrinsics:
            H, W = image_size_hw
            fy = (H / 2.0) / torch.tan(fov_h / 2.0)
            fx = (W / 2.0) / torch.tan(fov_w / 2.0)
            intrinsics = torch.zeros(pose_encoding.shape[:2] + (3, 3), device=pose_encoding.device)
            intrinsics[..., 0, 0] = fx
            intrinsics[..., 1, 1] = fy
            intrinsics[..., 0, 2] = W / 2
            intrinsics[..., 1, 2] = H / 2
            intrinsics[..., 2, 2] = 1.0  # Set the homogeneous coordinate to 1
    else:
        raise NotImplementedError

    return extrinsics, intrinsics