Mesh Ray Tracer

A BVH-accelerated ray-triangle intersection utility for triangle meshes, backed by nanort.

#include "geometrycentral/surface/mesh_ray_tracer.h"

#include "geometrycentral/surface/mesh_ray_tracer.h"
using namespace geometrycentral::surface;

// Build the acceleration structure once
MeshRayTracer tracer(geometry);

// Trace a ray — origin and direction, direction need not be normalized
RayHitResult hit = tracer.trace({0.5, 0.5, 10.0}, {0.0, 0.0, -1.0});

if (hit.hit) {
  // distance along ray
  double t = hit.t;

  // which triangle was hit
  size_t faceIdx = hit.faceIndex;

  // barycentric coords in that triangle
  Vector3 bary = hit.faceCoords;
}

The mesh must be triangulated. The BVH is built once at construction and can be queried any number of times.

Result struct

RayHitResult is returned by every trace() call.

struct RayHitResult {
  bool hit;           // true if the ray intersected the mesh
  double t;           // distance along the ray to the hit point
  size_t faceIndex;   // index of the hit face in the mesh
  Vector3 faceCoords; // barycentric coords in the hit face, in the same order as the face's vertices are given
};

Construction

MeshRayTracer::MeshRayTracer(EmbeddedGeometryInterface& geom)

Build the BVH over the triangles of geom‘s mesh. The mesh must be fully triangular.

MeshRayTracer::MeshRayTracer(const SimplePolygonMesh& mesh)

Build the BVH from a SimplePolygonMesh. All polygons must be triangles.

Queries

RayHitResult MeshRayTracer::trace(Vector3 origin, Vector3 dir) const

Trace a ray from origin in direction dir (need not be normalized).

Utilities

SurfacePoint toSurfacePoint(const RayHitResult& hit, SurfaceMesh& mesh)

Convert a RayHitResult to a SurfacePoint on mesh.

Only meaningful when the tracer was built from that mesh (or its geometry). Can only be called if the result was a hit.

The returned point is a face point with the hit’s barycentric coordinates.