How to account for edges with Mitsuba?

[jeertmans]

Hello!

As part of some Ray Tracing project, I'd like to add diffraction, for which I need edges.

Currently, I don't see any way for obtaining edges (on which diffraction can occur). I tried to manually incorporate them in the .ply files, but they are ignored:

Is there a workaround for that?

Thanks!

[njroussel]

Hi @jeertmans

The ply plugin only supports attributes on faces and vertices currently, hence the error message.

I'm not quite sure how I would go about implementing diffraction. I'm assuming you only want to consider a subsert of the shape's edges - in which case you'll need to modify the Mesh class to support edge attributes. Another approach would be to use face attributes and store something like a binary triplet to encode which of it's edges should be considered for diffraction.
Not quite sure what's the easiest/best solution for you.

[jeertmans]

Hi @njroussel, thanks for your answer :-)

Well, implementing diffraction will be done with one method I developed, but I only need diffraction candidates (so "exterior" edges).

As post-processing a mesh structure to obtain those edges is quite challenging (many vertices are duplicates, neighboring triangles introduce duplicated edges, co-planar edges must be discarded, ...), I would rather create a small-scale geometry by hand, and manually tell what are the "edges" I would like to consider.

Another solution is that I don't rely on .PLY file, but try to use the .OBJ or serialized formats. I should try this :-)

[ghost]

Hi, @jeertmans!

I am also interested in diffraction. I wonder how you could simulate it with a ray tracer. Could you give me some hints?

[jeertmans]

Hi @nick008a, it really depends if you are doing ray launching or ray tracing. It's a bit of self-promotion, but I wrote a paper about simulating diffraction (and others) on a radio propagation context: https://arxiv.org/abs/2301.06399. This is a very general (and not fast) method, but other exist, like minimizing the path length (Fermat's principle).

[ghost]

Thanks for the reply! Is this possible in mitsuba framework? Or do you have any good code base to get started?

[jeertmans]

With Mitsuba, you should implement all the diffraction from scratch. If you are into radio propagation, you can take a look at Sionna, which implements very basic diffraction. I am myself implementing my own framework, but it is not ready to use yet.