Recording paths of rays with PTracer Integrator and finding out how many hit a surface

[h-OUS-e]

Hello,

Sorry for the many questions, this topic is new to me. I would like to sample my own rays, and use these rays with the PTracer Integrator, and then record their paths. This is just to help visualize a few rays and how they travel through my scene setup. Is that possible without making my own integrator? The integrator examples I found written in python usually start from a sensor, but I was searching for something like a PTracer where rays are emitted from some location.

I would also like to calculate how many rays hit a particular spot on a mesh object to say that the more rays hit that same spot, the better it is, to guide an optimization problem.

Many thanks!

[njroussel]

I would like to sample my own rays, and use these rays with the PTracer Integrator, and then record their paths.

This is not possible out-of-the box. You would need to write your own integrator or at least replicate the main loop of the ptracer's sample method in a script.

I would also like to calculate how many rays hit a particular spot on a mesh object to say that the more rays hit that same spot, the better it is, to guide an optimization problem.

If you're only working with meshes, the SurfaceInteraction3f object (resulting of a ray-shape intersection) holds a pointer to the shape. If you need something more precise you can use the uv coordinates (assuming your object has a UV-mapping) or the prim_index field holds the index of the triangle the ray hit.

[h-OUS-e]

Thank you @njroussel, as a follow-up, is the ptracer's sample method written in Python? I couldn't find it in the integrator python example. Would I need to write one in C ++?

For the surfaceInteraction3f, how would I get that object from the scene after I render the scene with mi.render()?

[njroussel]

No it is written in C++, but you can port/rewrite it in Python.

You can not access it at the end of your render, you need access it at every step (bounce/intersection) of your integrator/script. Take another look at this tutorial how we get it from a ray intersection.

[h-OUS-e]

I am trying to write a Python version of the PTracer. From what I understoor, I can't inherit mi.SamplingIntegrator as it records rays starting from the sensor. Instead, I should inherit from mi.AdJointIntegrator since it does the rendering for rays starting from the light source. However, when I try to write:

lass MyPtracer(mi.AdjointIntegrator):

    def __init__(self, props=mi.Properties()):
        super().__init__(props)
        print("test")

and then register the integrator with mi.register_integrator("MyPtracer", lambda props: MyPtracer(props))
I get the error TypeError: MyPtracer: No constructor defined! after loading the scene. This error doesn't appear when I inherit from mi.SamplingIntegrator. How else should I write the initiation of the PTracer in python?

Sorry if this question is redundant, this is all a new territory to me.

[njroussel]

I believe this is a bug/limitation on our end. We have not enable the mechanism to extend AdjointIntegrator types. I will add that soon. I'll keep this thread updated.

[njroussel]

c4a8b31

This commit added the mechanism to extend AdjointIntegrator.