Ray Space Factorization for From-Region Visibility

Tommer Leyvand    Olga Sorkine    Daniel Cohen-Or



From-region visibility culling is considered harder than from-point visibility culling, since it is inherently four-dimensional. We present a conservative occlusion culling method based on factorizing the 4D visibility problem into horizontal and vertical components. The visibility of the two components is solved asymmetrically: the horizontal component is based on a parameterization of the ray space, and the visibility of the vertical component is solved by incrementally merging umbrae. The technique is designed so that the horizontal and vertical operations can be efficiently realized together by modern graphics hardware.
Similar to image-based from-point methods, we use an occlusion map to encode visibility; however, the image-space occlusion map is in the ray space rather than in the primal space.
Our results show that the culling time and the size of the computed potentially visible set depend on the size of the viewcell. For moderate viewcells, conservative occlusion culling of large urban scenes takes less than a second, and the size of the potentially visible set is only about two times larger than the size of the exact visible set.

SIGGRAPH 2003 Paper (6.4MB, PDF)

SIGGRAPH 2003 Video* (on YouTube)

M.Sc. Thesis (2MB, PDF, extended version)

Urban model generator CityGen is available online here.

BibTeX entry:

 author = {Tommer Leyvand and Olga Sorkine and Daniel Cohen-Or},
 title = {Ray space factorization for from-region visibility},
 journal = {ACM Transactions on Graphics (TOG)},
 volume = {22},
 number = {3},
 year = {2003},
 issn = {0730-0301},
 pages = {595--604},
 doi = {http://doi.acm.org/10.1145/882262.882313},
 publisher = {ACM Press},

SIGGRAPH 2003 presentation:
Power Point XP, 3.7MB

High-Res, AVI DivX 5 Video*, 29MB

Low-Res, AVI DivX 5 Video*, 16MB

* The latest DivX codec is freely available here

Some results:
(Click on an image to enlarge

Random City Model:

Vienna2000 Model:

Box-Field Model:

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