open3d / embree seems to return nothing when ray hits a vertex exactly?

[pwais]

dear o3d peeps,

i tried raycasting using code very similar to the demo and plotting the result as is done here:

Open3D/examples/python/geometry/ray_casting_to_image.py

Line 37 in 6ddbcd5

plt.imshow(ans['t_hit'].numpy())

in my scene, I have rays that actually exactly correspond to vertices of the input mesh, and thus I'd expect the embree / open3d raycaster to return vertex hits. but the actual output appears to be a lot of misses / 0 depth returns:

When I offset the entire vertices mesh by epsilon, then I get ray-triangle intersections that make sense:

Looking at the source code and embree, it's actually not really clear... what embree is supposed to return if a ray hits a vertex exactly?

It's worth noting that Open3D uses rtcIntersect1M() https://github.com/isl-org/Open3D/blob/6ddbcd5c9b8bf0b496e4151c7d7766af09e3dba7/cpp/open3d/t/geometry/RaycastingScene.cpp#L318C13-L318C27

which is supposed to be deprecated and removed in the most recent version of embree: https://github.com/embree/embree/blob/0fcb306c9176221219dd15e27fe0527ed334948f/README.md?plain=1#L1383

I wonder if using the new API will result in well-defined output for when a ray intersects a vertex?

[benjaminum]

Hi @pwais,
Hitting exactly a vertex is a corner case. I wonder why there are so many direct hits in your case.
Are the rays defined in a specific way that makes this more likely?

[pwais]

yes by construction there are lots of vertex hits. oddly I see the issue go away after I built open3d from source. But Dr Woop says actually I should not see so many issues on default dembree. I will investigate further.