Ray-tracing and path tracing have been a constant research area of computer graphics and other disciplines, e.g. seismic raytracing in geophysics or heat flow modeling.
A major drawback of this techniques is the high computational cost, in particular due to ray-mesh intersection and finding the intersected triangle. A common solution is to use acceleration structures like BVHs (Bounding volume hierarchies), Octrees or Grids.
In their 2008 paper "Accelerating Raytracing Using Constrained Tetrahedralizations" Lagae & Dutre explored the idea of using a tetrahedral mesh for fast search of the intersection point. Their approach was
to subdivide the complete scene into tetrahedra and use neighbor-relations between tetrahedra to quickly find the triangle intersected by a ray.
This project aims to expand their idea by using GPGPU with Nvidia CUDA to speed up the calculations. The Tetgen software developed by Hang Si(http://wias-berlin.de/software/tetgen/) is used for tetrahedralization of the scene.


Development images:


Fig. 1: Cornell box scene.


Fig. 2: Visualization of the tetrahedral acceleration mesh.

References:

Hang Si (2015). TetGen, a Delaunay-Based Quality Tetrahedral Mesh Generator. ACM Trans. on Mathematical Software. 41 (2), Article 11 (February 2015), 36 pages.

Lagae, A. and Dutre, P. (2008). Accelerating Ray Tracing using Constrained Tetrahedralizations. Computer Graphics Forum, 27: 1303-1312.

Sanzenbacher, S. (2010) Darstellung von Kaustiken und Lichtstreuung in Interaktiven Anwendungen. Unpublished diploma thesis, Institut fuer Visualisierung und Interaktive Systeme, University Stuttgart.


Github link: github.com/clehmann-geo/tetra_mesh

Current status (04/22/2016):

Import Tetgen files .node/.ele/.face/.edge/.neigh - done!
Ray-tetrahedra intersection routine - done!
Ray-in-tetrahedra-testing routine - done!
Find tetrahedra with camer position - done!
CUDA kernel for ray traversal - done!
Ray-triangle intersection routine for raytracing - done!
visualize depth information - done!
mesh in unified memory - done!!
cuda raytracing kernel - done!!
screen output - done!!
keyboard input - done!!
mouse input - done!!
support for specular/refractive/diffuse materials - done!!
path tracing - done!!!
visualize mesh - done!!
print debug info onscreen - done!!


Todo:
implement volumetric path tracing
properties of tetrahedra - friction etc.
Implement mesh deformation - Mueller et al. (2015)