World coordinate system

[chenguolin]

It seems that the preprocessing of the DL3DV world coordinate system is incorrect.

In the latest NerfStudio:
https://github.com/nerfstudio-project/nerfstudio/blob/main/nerfstudio/process_data/colmap_utils.py#L445-L449

# Convert from COLMAP's camera coordinate system (OpenCV) to ours (OpenGL)
c2w[0:3, 1:3] *= -1
if not keep_original_world_coordinate:
    c2w = c2w[np.array([0, 2, 1, 3]), :]
    c2w[2, :] *= -1

However, in

NoPoSplat/src/scripts/convert_dl3dv.py

Lines 65 to 71 in a427bd7

	def opengl_c2w_to_opencv_w2c(c2w: np.ndarray) -> np.ndarray:
	c2w = c2w.copy()
	c2w[2, :] *= -1
	c2w = c2w[np.array([1, 0, 2, 3]), :]
	c2w[0:3, 1:3] *= -1
	w2c_opencv = np.linalg.inv(c2w)
	return w2c_opencv

Should c2w = c2w[np.array([1, 0, 2, 3]), :] be c2w = c2w[np.array([0, 2, 1, 3]), :]?

Or is this a problem of NerfStudio version, as I found the same code as this repo in a NerfStudio issue (May 19, 2023)
nerfstudio-project/nerfstudio#1708 (comment)

c2w = np.linalg.inv(w2c)
# Convert from COLMAP's camera coordinate system (OpenCV) to ours (OpenGL)
c2w[0:3, 1:3] *= -1
c2w = c2w[np.array([1, 0, 2, 3]), :]
c2w[2, :] *= -1

[chenguolin]

It seems like indeed a bug fixed recently by NerfStudio (2024.Jan.19): nerfstudio-project/nerfstudio#2793

So c2w = c2w[np.array([0, 2, 1, 3]), :] should be correct and reasonable for me.