# Source code for pytorch3d.utils.camera_conversions

```
# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.
from typing import Tuple
import torch
from ..renderer import PerspectiveCameras
from ..renderer.camera_conversions import (
_cameras_from_opencv_projection,
_opencv_from_cameras_projection,
_pulsar_from_cameras_projection,
_pulsar_from_opencv_projection,
)
[docs]def cameras_from_opencv_projection(
R: torch.Tensor,
tvec: torch.Tensor,
camera_matrix: torch.Tensor,
image_size: torch.Tensor,
) -> PerspectiveCameras:
"""
Converts a batch of OpenCV-conventioned cameras parametrized with the
rotation matrices `R`, translation vectors `tvec`, and the camera
calibration matrices `camera_matrix` to `PerspectiveCameras` in PyTorch3D
convention.
More specifically, the conversion is carried out such that a projection
of a 3D shape to the OpenCV-conventioned screen of size `image_size` results
in the same image as a projection with the corresponding PyTorch3D camera
to the NDC screen convention of PyTorch3D.
More specifically, the OpenCV convention projects points to the OpenCV screen
space as follows:
```
x_screen_opencv = camera_matrix @ (R @ x_world + tvec)
```
followed by the homogenization of `x_screen_opencv`.
Note:
The parameters `R, tvec, camera_matrix` correspond to the outputs of
`cv2.decomposeProjectionMatrix`.
The `rvec` parameter of the `cv2.projectPoints` is an axis-angle vector
that can be converted to the rotation matrix `R` expected here by
calling the `so3_exp_map` function.
Args:
R: A batch of rotation matrices of shape `(N, 3, 3)`.
tvec: A batch of translation vectors of shape `(N, 3)`.
camera_matrix: A batch of camera calibration matrices of shape `(N, 3, 3)`.
image_size: A tensor of shape `(N, 2)` containing the sizes of the images
(height, width) attached to each camera.
Returns:
cameras_pytorch3d: A batch of `N` cameras in the PyTorch3D convention.
"""
return _cameras_from_opencv_projection(R, tvec, camera_matrix, image_size)
[docs]def opencv_from_cameras_projection(
cameras: PerspectiveCameras,
image_size: torch.Tensor,
) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
"""
Converts a batch of `PerspectiveCameras` into OpenCV-convention
rotation matrices `R`, translation vectors `tvec`, and the camera
calibration matrices `camera_matrix`. This operation is exactly the inverse
of `cameras_from_opencv_projection`.
Note:
The outputs `R, tvec, camera_matrix` correspond to the outputs of
`cv2.decomposeProjectionMatrix`.
The `rvec` parameter of the `cv2.projectPoints` is an axis-angle vector
that can be converted from the returned rotation matrix `R` here by
calling the `so3_log_map` function.
Args:
cameras: A batch of `N` cameras in the PyTorch3D convention.
image_size: A tensor of shape `(N, 2)` containing the sizes of the images
(height, width) attached to each camera.
return_as_rotmat (bool): If set to True, return the full 3x3 rotation
matrices. Otherwise, return an axis-angle vector (default).
Returns:
R: A batch of rotation matrices of shape `(N, 3, 3)`.
tvec: A batch of translation vectors of shape `(N, 3)`.
camera_matrix: A batch of camera calibration matrices of shape `(N, 3, 3)`.
"""
return _opencv_from_cameras_projection(cameras, image_size)
[docs]def pulsar_from_opencv_projection(
R: torch.Tensor,
tvec: torch.Tensor,
camera_matrix: torch.Tensor,
image_size: torch.Tensor,
znear: float = 0.1,
) -> torch.Tensor:
"""
Convert OpenCV style camera parameters to Pulsar style camera parameters.
Note:
* Pulsar does NOT support different focal lengths for x and y.
For conversion, we use the average of fx and fy.
* The Pulsar renderer MUST use a left-handed coordinate system for this
mapping to work.
* The resulting image will be vertically flipped - which has to be
addressed AFTER rendering by the user.
* The parameters `R, tvec, camera_matrix` correspond to the outputs
of `cv2.decomposeProjectionMatrix`.
Args:
R: A batch of rotation matrices of shape `(N, 3, 3)`.
tvec: A batch of translation vectors of shape `(N, 3)`.
camera_matrix: A batch of camera calibration matrices of shape `(N, 3, 3)`.
image_size: A tensor of shape `(N, 2)` containing the sizes of the images
(height, width) attached to each camera.
znear (float): The near clipping value to use for Pulsar.
Returns:
cameras_pulsar: A batch of `N` Pulsar camera vectors in the Pulsar
convention `(N, 13)` (3 translation, 6 rotation, focal_length, sensor_width,
c_x, c_y).
"""
return _pulsar_from_opencv_projection(R, tvec, camera_matrix, image_size, znear)
[docs]def pulsar_from_cameras_projection(
cameras: PerspectiveCameras,
image_size: torch.Tensor,
) -> torch.Tensor:
"""
Convert PyTorch3D `PerspectiveCameras` to Pulsar style camera parameters.
Note:
* Pulsar does NOT support different focal lengths for x and y.
For conversion, we use the average of fx and fy.
* The Pulsar renderer MUST use a left-handed coordinate system for this
mapping to work.
* The resulting image will be vertically flipped - which has to be
addressed AFTER rendering by the user.
Args:
cameras: A batch of `N` cameras in the PyTorch3D convention.
image_size: A tensor of shape `(N, 2)` containing the sizes of the images
(height, width) attached to each camera.
Returns:
cameras_pulsar: A batch of `N` Pulsar camera vectors in the Pulsar
convention `(N, 13)` (3 translation, 6 rotation, focal_length, sensor_width,
c_x, c_y).
"""
return _pulsar_from_cameras_projection(cameras, image_size)
```