Add backward gradients for camera intrinsics

[arthurhero]

Hi,

Thank you for the great work! May I ask if you have plan to add gradients for camera intrinsics (fxfycxcy)? I think there are gradients provided for extrinsics already. It would be great to have gradients for intrinsics as well!

Thank you very much,
Ziwen

[zhanglq2024]

I'm also very interested in this problem. If we can make the intrinsics differentiable, we might not need COLMAP or bundle adjustment anymore.

[nlml]

See this new paper! https://arxiv.org/html/2502.19800v1
I might look into implementing it for gsplat...

[nlml]

Got this working (I think) !
PR here: #801

[arthurhero]

Got this working (I think) ! PR here: #801

Looks like a huge amount of work! Thank you, Liam! I will try it out

[nlml]

@arthurhero no worries! Let me know if it seems to work for you, I haven't tested it deeply yet.