ray trace in 3d volume mesh

[fab6]

Hi,

I pretty new to bvh and your implementation :-) Now I am a bit curious if I can apply it to calculate the path of a ray inside a 3d volume mesh. Looking at meshio it seems that one can read gmsh meshes, but I am not sure if this actually the use case!?
So one needs to extract the path inside each volume cell in combination with cell information like temperature.

I tried your example with a simple cube to understand a bit better what I can get out:

mesh = load("cube_default.obj")

# Generate bounding spheres around each triangle in the mesh
bounding_spheres = [BSphere{Float32}(tri) for tri in mesh]

# Build BVH
bvh = BVH(bounding_spheres, BBox{Float32}, UInt32)

points =[-10; 0; 0]
directions =[ 10; 0; 0]
# Traverse BVH to get indices of rays intersecting the bounding spheres
traversal = traverse_rays(bvh, points, directions)
@show traversal.contacts
println(traversal)

The cube is just:

v 1.000000 1.000000 -1.000000
v 1.000000 -1.000000 -1.000000
v 1.000000 1.000000 1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 1.000000 -1.000000
v -1.000000 -1.000000 -1.000000
v -1.000000 1.000000 1.000000
v -1.000000 -1.000000 1.000000
f 1/1/1 5/2/1 7/3/1 3/4/1
f 4/5/2 3/4/2 7/6/2 8/7/2
f 8/8/3 7/9/3 5/10/3 6/11/3
f 6/12/4 2/13/4 4/5/4 8/14/4
f 2/13/5 1/1/5 3/4/5 4/5/5
f 6/11/6 5/10/6 1/1/6 2/13/6

The output is, but I don't understand yet what this means

traversal.contacts = Tuple{Int32, Int32}[(5, 1), (6, 1), (7, 1), (8, 1), (11, 1), (12, 1), (3, 1), (4, 1), (1, 1), (2, 1), (9, 1), (10, 1)]

I expected (hoped) that it gives me somehow the info of the intersection of the left surface and right surface of the cube.
Probably I complete misunderstood the approach and did not check in detail the documentation...

Maybe you have some info for my questions?
This would be great!

Best Regards
Fab

[fab6]

Hi,
probably I misunderstood the BVH approach and the current implementation. It seems the output gives me "only" the intersections of the bounding sphere or boxes.

And with isintersection I can check if there is an intersection of a particual bounding box/sphere, but not the exact position and therefore also not the exact distance between two intersections. Is this right?

And with a slight adjustment (bounding_box = [BBox{Float32}(tri) for tri in mesh]) I get the output:

traversal.contacts = Tuple{Int32, Int32}[(5, 1), (6, 1), (9, 1), (10, 1)]

Which gives me the number of the intersecting box for each ray (in my case only 1).

And the actual size of the bounding boxes is given by simply printing it (here with adding the number and a mark to 5,6,9,10):

BBox{Float32}[
 1 BBox{Float32}((-1.0f0, 1.0f0, -1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
 2 BBox{Float32}((-1.0f0, 1.0f0, -1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
 3 BBox{Float32}((-1.0f0, -1.0f0, 1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
 4 BBox{Float32}((-1.0f0, -1.0f0, 1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
 5* BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (-1.0f0, 1.0f0, 1.0f0)), 
 6* BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (-1.0f0, 1.0f0, 1.0f0)), 
 7 BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (1.0f0, -1.0f0, 1.0f0)), 
 8 BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (1.0f0, -1.0f0, 1.0f0)), 
 9* BBox{Float32}((1.0f0, -1.0f0, -1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
10* BBox{Float32}((1.0f0, -1.0f0, -1.0f0), (1.0f0, 1.0f0, 1.0f0)), 
11 BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (1.0f0, 1.0f0, -1.0f0)), 
12 BBox{Float32}((-1.0f0, -1.0f0, -1.0f0), (1.0f0, 1.0f0, -1.0f0))
]

The ray starts and its direction is still:

points =[-10; 0; 0]
directions =[ 10; 0; 0]

So box 5 and box 10 make sense to me, I still have trouble with box 6 and 9.

Do you have a hint how I can understand the box traversal better and how I get the intersection position of the actual element (if this is possible)?
Thanks