title =      "CHC+RT: Coherent Hierarchical Culling for Ray Tracing",
  author =     "Oliver Mattausch and Jirí Bittner and  Alberto Jaspe Villanueva and  Enrico Gobbetti, 
                Michael Wimmer and Renato Pajarola",
  year =       "2015",
  pages =      "537--548",
  month =      may,
  number =     "2",
  event =      "EUROGRAPHICS 2015",
  journal =    "Computer Graphics Forum",
  volume =     "34",
  location =   "Zurich",
  keywords =   "occlusion culling, ray tracing, out-of-core",
  abstract="We propose a new technique for in-core and out-of-core GPU ray tracing using a generalization 
of hierarchical occlusion culling in the style of the CHC++ method. Our method exploits the rasterization 
pipeline and hardware occlusion queries in order to create coherent batches of work for localized 
shader-based ray tracing kernels. By combining hierarchies in both ray space and object space, the method 
is able to share intermediate traversal results among multiple rays. We exploit temporal coherence among 
similar ray sets between frames and also withinthe given frame. A suitable management of the current 
visibility state makes it possible to benefit from occlusion culling for less coherent ray types like 
diffuse reflections. Since large scenes are still a challenge for modern GPU ray tracers, our method is 
most useful for scenes with medium to high complexity, especially since our method inherently supports ray 
tracing highly complex scenes that do not fit in GPU memory. For in-core scenes our method is comparable to 
CUDA ray tracing and performs up to 5.94x better than pure shader-based ray tracing."