Projecting 2D Coordinates onto Non-Flat Terrain to Obtain Z-Coordinate Using Sionna

[Chartist-1]

Hello,
I have a set of [x, y] coordinates representing the position of an object in a 2D plane. My goal is to project these coordinates onto a non-flat terrain to compute the corresponding z-coordinate.

Currently, I’ve implemented this process in Blender, where I can successfully project the points onto the terrain mesh and retrieve the z-coordinate. However, I’m looking for a more efficient and programmatic solution that doesn’t rely on Blender.

I’ve been exploring Sionna , if there are any tools or utilities within the library that could help me achieve this task. Specifically:
RayCasting, so i can get hit location coordinates.

Thanks in advance

[merlinND]

Hello @Chartist-1,

If you know which shape (mesh) represents the terrain in your scene, I think it should be able to directly perform ray intersection against it with Shape.ray_intersect(): https://mitsuba.readthedocs.io/en/stable/src/api_reference.html#mitsuba.Shape.ray_intersect

If that doesn't directly work, two possible workarounds would be:

• Create a small Mitsuba scene with mi.load_dict() containing only your terrain mesh and call Scene.ray_intersect() (this one should work for sure)
• Repeatedly call Mesh.ray_intersect_triangle(). But I don't recommend this since it will not scale well with the number of triangles in your terrain mesh.

[Chartist-1]

Thank you very much for your help—it worked perfectly!
For anyone else searching for a solution to a similar problem, here’s the code I used:

import mitsuba as mi

scene = mi.load_file('your_file.xml')

ray = mi.Ray3f(
o=mi.Point3f([x, y, 1000]), # Ray origin from the top
d=mi.Vector3f([0, 0, -1]) # Ray direction: pointing downward along the Z-axis
)
intersection = scene.ray_intersect(ray)

print(intersection)