@InProceedings{Engelhardt09-GVQ,
  author = {Thomas Engelhardt and Carsten Dachsbacher},
  title  = {{Granular Visibility Queries}},
  year   = {2009},
  pages  = {161-167},
  booktitle = {{Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games}}
}