Transformation between opf geographic coordinates and nerfstudio coordinates

[Wjppppp]

Hi,

thank you so much for providing opf conversion tools! This is very helpful.

I used opf2nerf project.opf --out-dir out_dir/ --nerfstudio to convert opf folder to a folder ready-for-use in nerfstudio.

Then I trained the model in nerfstudio, exported the outputs as point clouds with the arguement --save-world-frame. However, I found the exported point cloud's coordinates can not match neither the geographic coordinates nor coordinates in colmap/points3D.txt. I struggled a lot to find the correct transformation.

Then I dive into opf2nerf/converter.py, I found the scale, avg_pos are not written out anywhere.

pyopf/src/opf_tools/opf2nerf/converter.py

Line 173 in ec60ebe

def rescale_position(

But these two variables are actually needed to convert the point clouds derived out of nerfstudio into geographic coordinates through an inverse transformation like:

geo_position = (nerf_position * scale) + avg_pos

please let me know if I was wrong.

Could you please also improve the tool, enabling to explicitly write out the scale and avg_pos to some place when using opf2nerf --nerfstudio? It would be nice to mention how to correctly use --cam-aabb-size as well.

Thank you!

[pani-vishal]

Hi there,

The --cam-aabb-size is used to rescale the camera positions so that they are in a 8x8x8 cube. This was done to match the original NeRF experiments on the synthetic datasets which places the cameras on a 4m radius circle. Since the original NeRF implementation models foreground within a fixed length box (please refer here), this ensured compatibility with previous NeRF implementations that we were targeting before nerfstudio.

It seems that nerfstudio doesn't require it anymore.

However, the transformation to get back the geographic coordinates looks correct! To maintain back-compatibility we are working on writing out the scale and avg_pos to help you get back the geographic coordinates :)

[krahenbuhl]

#14 should hopefully help with your issue @Wjppppp