# Fast and Accurate Visibility Preprocessing

Nirenstein, Shaun (2003) *Fast and Accurate Visibility Preprocessing*. PhD, Department of Computer Science, University of Cape Town.

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## Abstract

Visibility culling is a means of accelerating the graphical rendering of geometric models. Invisible objects are efficiently culled to prevent their submission to the standard graphics pipeline. It is advantageous to preprocess scenes in order to determine invisible objects from all possible camera views. This information is typically saved to disk and may then be reused until the model geometry changes. Such preprocessing algorithms are therefore used for scenes that are primarily static.

Currently, the standard approach to visibility preprocessing algorithms is to use a form of approximate solution, known as conservative culling. Such algorithms over-estimate the set of visible polygons. This compromise has been considered necessary in order to perform visibility preprocessing quickly. These algorithms attempt to satisfy the goals of both rapid preprocessing and rapid run-time rendering.

We observe, however, that there is a need for algorithms with superior performance in preprocessing, as well as for algorithms that are more accurate. For most applications these features are not required simultaneously. In this thesis we present two novel visibility preprocessing algorithms, each of which is strongly biased toward one of these requirements.

The first algorithm has the advantage of performance. It executes quickly by exploiting graphics hardware. The algorithm also has the features of output sensitivity (to what is visible), and a logarithmic dependency in the size of the camera space partition. These advantages come at the cost of image error. We present a heuristic guided adaptive sampling methodology that minimises this error. We further show how this algorithm may be parallelised and also present a natural extension of the algorithm to five dimensions for accelerating generalised ray shooting.

The second algorithm has the advantage of accuracy. No over-estimation is performed, nor are any sacrifices made in terms of image quality. The cost is primarily that of time. Despite the relatively long computation, the algorithm is still tractable and on average scales slightly superlinearly with the input size. This algorithm also has the advantage of output sensitivity. This is the first known tractable exact solution to the general 3D from-region visibility problem.

In order to solve the exact from-region visibility problem, we had to first solve a more general form of the standard stabbing problem. An efficient solution to this problem is presented independently.

EPrint Type: | Electronic Thesis or Dissertation |
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Keywords: | Visibility, Graphics Hardware, Comptuational Geometry, CSG, Plucker, Projective Geometry |

Subjects: | I Computing Methodologies: I.3 COMPUTER GRAPHICS F Theory of Computation: F.2 ANALYSIS OF ALGORITHMS AND PROBLEM COMPLEXITY G Mathematics of Computing: G.4 MATHEMATICAL SOFTWARE |

ID Code: | 101 |

Deposited By: | Nirenstein, Shaun |

Deposited On: | 24 Febuary 2004 |

Alternative Locations: | http://people.cs.uct.ac.za/~snirenst/thesis.pdf |