pyraymesh 0.2.4

A library for ray-mesh intersections on triangular meshes

pyraymesh

Description

pyraymesh is a Python library for performing ray intersection and occlusion tests on 3D meshes using a Bounding Volume Hierarchy (BVH). The library uses the C++ library bvh for building the BVH and performing the intersection tests.

While this library is reasonably fast for simpler meshes (benchmarks coming soon), it is not as fast as Embree, espcially for larger and more complex meshes. However, it does not have any dependencies on external libraries, and is thus easier to install and use.

Installation

Install the package either by

pip install pyraymesh

or cloning the repo and using pip:

pip install .

Note that the package requires a C++ compiler to build the C++ extension.

Usage

Building the BVH

To build the BVH for a mesh:

from pyraymesh import Mesh
import numpy as np

vertices = np.array([[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0]])
faces = np.array([[0, 1, 2], [2, 3, 0]])
mesh = Mesh(vertices, faces)
mesh.build("medium")

The build method takes a string argument that specifies the BVH build type, which can be one of the following: "low", "medium" and "high". The build type determines the trade-off between build time and query time. For most cases "medium" is almost always the right choice.

Ray Intersection

To perform ray intersection tests:

ray_origin = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
ray_direction = [[0, 0, -1], [0, 0, 1]]
## or 
ray_origin = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
ray_direction = [0, 0, -1]  # multiple rays with same direction
## or 
ray_origin = [0.1, 0.2, 1]
ray_direction = [[0, 0, -1], [0, 0, 1]]  # multiple rays with same origin

result = mesh.intersect(ray_origin, ray_direction, tnear=0, tfar=1000)
print(result.num_hits)
print(result.coords)
print(result.tri_ids)
print(result.distances)

tnear and tfar can be scalars or lists of the same length as the number of rays. If they are scalars, the same value will be used for all rays. If they are lists, each value will be used for the corresponding ray.

If you set tnear to a value greater than 0, the intersection tests will ignore any intersections that are closer than tnear. Similarly, if you set tfar to a value less than infinity, the intersection tests will ignore any intersections that are farther than tfar. This library does not support negative values for tnear or tfar.

Reflections

If you want to get the reflection of the rays, add the calculate_reflections = True parameter to the intersect method:

ray_origin = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
ray_direction = [[0, 0, -1], [0, 0, 1]]
result = mesh.intersect(ray_origin, ray_direction, tnear=0, tfar=1000, calculate_reflections=True)
print(result.reflections)

results.reflections is a list of noramlized vectors representing the directions of the reflection of the rays. Only do this if you need the reflections, as it will slow down the intersection tests.

Occlusion Test

If you just care about whether a ray is occluded or not (i.e., you don't care about the intersection point) you can use the occlusion method which is faster than the intersect method and just returns an array of booleans.

ray_origin = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
ray_direction = [[0, 0, -1], [0, 0, 1]]
occluded = mesh.occlusion(ray_origin, ray_direction)
print(occluded)

Count intersections

If you want to know the total number of intersections for each ray along its path, without stopping at the first intersection, you can use the count_intersections method:

total_intersections = mesh.count_intersections(ray_origin, ray_direction)
print(total_intersections)

This method returns an array of integers representing the total number of triangles that each ray intersects between tnear and tfar.

Test line-of-sight

If you want to know if two points are visible to each other, you can use the line_of_sight method:

origin_point = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
target_point = [[0, 0, -1], [0, 0, 1]]
## or 
origin_point = [[0.1, 0.2, 1], [0.2, 0.1, 1]]
target_point = [0, 0, -1]  # multiple origin points with same target
## or 
origin_point = [0.1, 0.2, 1]
target_point = [[0, 0, -1], [0, 0, 1]]  # multiple target points with same origin

visible = mesh.line_of_sight(origin_point, target_point)

visible is a list of booleans representing whether the target point is visible from the origin point.

Visibility Matrix

If you want to know the visibility matrix between all pairs of a list of points, you can use the visibility_matrix method: For N points it returns an NxN matrix where the element at (i, j) is True if the j-th point is visible from the i-th point.

points = [[0.1, 0.2, 1], [0.2, 0.1, 1], [0.3, 0.4, 1]]
vis_matrix = mesh.visibility_matrix(points)
# vis_matrix is a 3x3 array of booleans

Traverse the BVH

If you want to traverse the BVH and get all triangles that are along a ray in the BVH, you can use the traverse method. This is useful if you want to do some custom processing on the triangles that are potentially intersected by a ray.

origin = [0, 0, 10]
direction = [0, 0, -1]

for t_id in mesh.traverse(origin, direction):
    print(f"Triangle {mesh.vertices[mesh.faces[t_id]]} is potentially intersected by the ray.")

Note that the current implementation traverses the entire BVH when the method is called, even if you break early from the loop. For huge meshes, this can be a performance bottleneck. Hopefully, this will be fixed in future versions.

Parallelization

The intersect and occlusion methods can be parallelized by passing threads parameter when calling the methods:

result = mesh.intersect(ray_origin, ray_direction, tnear=0, tfar=1000, threads=4)

The threads parameter specifies the number of threads to use for the intersection tests. If set to -1, the number of threads will be equal to the number of cores on the machine. In general you shouldn't set the number of threads to be greater than the number of cores on the machine.

For a small number of rays, the overhead of parallelization might make the parallel version slower than the serial version, so it is recommended to test the performance of both versions for your specific use case.

Testing

To run the tests:

pytest

License

This project is licensed under the MIT License - see the LICENSE file for details.