Intersection from Ray Perpendicular to Vertex not Consistent

[Iciar]

To find some intersections of triangles in the same plane, I am using Embree to create the scene and then shooting a ray through each triangle vertex going perpendicular to the plane of the triangles. I then use rtcIntersect to find what triangles the ray intersects with in the scene.

This seems to work in some of the cases but in others it is not getting all the intersections. In the image I attached, for example, when I shoot a ray through the red vertex, the intersect function finds intersections with all the triangles except for the one I outlined blue, which also shares that vertex. Does this happen because of the offset in 2D cases to avoid division by 0? Is there any way I could ensure all the triangles that share that vertex and all those intersected are returned?

Thanks.

[SvenW_Intel · Accepted solution]

If you shoot rays exactly at a vertex you will not have a guaranteed intersection. You can improve the situation by enabling the RTC_SCENE_FLAG_ROBUST, which will guarantee hits along the edge, but the vertex will still sometimes cause issues.

Principally this can get fixed, but at the loss of some performance. As the library is designed for rendering we have chosen to allow these very rare misses at the vertex.