Rana, S.; (2006) Development of ray tracing algorithms in GIS for urban visibility analysis. Presented at: 2006 Meeting of the AAG (American Association of Geographers), Chicago, USA.

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Abstract

Urban visibility analysis deals with the computation and analysis of urban open spaces and street networks. Traditionally, due to it's predominantly architecture-discipline related lineage, urban visibility analysis was mostly carried out in the fields of architecture and urban planning. However, recently GIS researchers have used urban visibility analysis for pedestrian simulation, planning of visual surveillance and analysis of the structure of open spaces. The aim of this talk is to demonstrate the concepts and GIS-based implementation of ray tracing techniques for the computation of visibility in urban open spaces. Ray tracing is a fairly common computer graphics technique for identifying visible objects in a scene (e.g. in computer games). In ray tracing, a line of sight or ray is drawn at very small equal angular intervals (<=0.1 degrees) from the viewpoint and the intersection points of the ray with the obstacles are collated to form the scene visible from the viewpoint. A simple ray tracing is computationally very demanding hence it will be shown how heuristics such as Binary Space Partitioning can be used to reduce the computation time significantly. Paper will demonstrate the Isovist Analyst, an extension to the popular GIS ArcView, which incorporates the ray tracing approach for visibility computation. As examples, talk will demonstrate the use of visibility computation in planning visual surveillance, pedestrian simulation, and characterizing the structure of open spaces.

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