title =      "Efficient Online Visibility for Shadow Maps",
  author =     "Oliver Mattausch and Ji{\v r}{\' i} Bittner and Ari
               Silvennoinen and Daniel Scherzer and Michael Wimmer",
  year =       "2012",
  abstract =   "Standard online occlusion culling is able to vastly improve
               the rasterization performance of walkthrough applications by
               identifying large parts of the scene as invisible from the
               camera and rendering only the visible geometry. However, it
               is of little use for the acceleration of shadow map
               generation (i.e., rasterizing the scene from the light view
               [Williams 78]), so that typically a high percentage of the
               geometry will be visible when rendering shadow maps. For
               example, in outdoor scenes typical viewpoints are near the
               ground and therefore have significant occlusion, while light
               viewpoints are higher up and see most of the geometry. Our
               algorithm remedies this situation by quickly detecting and
               culling the geometry that does not contribute to the shadow
               in the final image.",
  month =      feb,
  booktitle =  "GPU Pro 3: Advanced Rendering Techniques",
  editor =     "Wolfgang Engel",
  isbn =       "978-1439887820",
  publisher =  "CRC Press",
  keywords =   "shadow maps, visibility culling",
  pages =      "233–-242"