Incorrect handling of distortion parameters in `colmap.py`

[MomokoMatsuo]

Currently, distortion parameters are read as follows:

# Get distortion parameters.
type_ = cam.model
if type_ == CameraModelId.SIMPLE_PINHOLE:
    params = np.empty(0, dtype=np.float32)
    camtype = "perspective"
elif type_ == CameraModelId.PINHOLE:
    params = np.empty(0, dtype=np.float32)
    camtype = "perspective"
if type_ == CameraModelId.SIMPLE_RADIAL:
    params = np.array([cam.params[4], 0.0, 0.0, 0.0], dtype=np.float32)
    camtype = "perspective"
elif type_ == CameraModelId.RADIAL:
    params = np.array([cam.params[4], cam.params[5], 0.0, 0.0], dtype=np.float32)
    camtype = "perspective"
elif type_ == CameraModelId.OPENCV:
    params = np.array([cam.params[4], cam.params[5], cam.params[6], cam.params[7]], dtype=np.float32)
    camtype = "perspective"
elif type_ == CameraModelId.OPENCV_FISHEYE:
    params = np.array([cam.params[4], cam.params[5], cam.params[6], cam.params[7]], dtype=np.float32)
    camtype = "fisheye"
assert (
    camtype == "perspective" or camtype == "fisheye"
), f"Only perspective and fisheye cameras are supported, got {type_}"

However, the indexing of cam.params is incorrect.
For example, in COLMAP’s camera models (see [colmap/models.h](https://github.com/colmap/colmap/blob/main/src/colmap/sensor/models.h)):

SimpleRadialCameraModel: f, cx, cy, k1, k2
RadialCameraModel: fx, fy, cx, cy, k1, k2, p1, p2
OpenCVCameraModel: fx, fy, cx, cy, k1, k2, k3, k4
OpenCVFisheyeCameraModel: fx, fy, cx, cy, k1, k2, p1, p2, k3, k4, k5, k6

This means, for example, that in SIMPLE_RADIAL, the correct index for k1 should be cam.params[3], not cam.params[4].
In general, except for SIMPLE_PINHOLE, all current models appear to be shifted by one index.

I searched the repository to check if this issue was already reported, but I could not find anything. Apologies if it has already been addressed.

[MomokoMatsuo]

I'm sorry, I noticed that issue was not in current main branch.
I was using the PR: #536 .

I close this one.