Visibility and viewshed algorithms in an information system for environmental management

Summarization: Viewshed calculation is one of the basic procedures existing in an Information System, which has the ability to manage elevation data. Visibility calculation used to be a very time consuming procedure. The rapid development of computer technology propagated the demand for faster and better algorithms, of higher quality and of a more sophisticated logic. Viewshed depends on the height of the viewing point. The alteration of this height brings alteration of the viewshed. Different techniques have been developed concerning the different ways according to which: (a) data are collected from the Digital Elevation Model (DEM) for the viewshed calculation, (b) Visual Point and Target Point is defined horizontally and vertically, (c) the decision VISIBLE or NOT VISIBLE is taken for a point. An answer \“VISIBLE” or \“NOT” is not enough information to define if a point is really visible or not. Visibility depends on a series of factors and conditions that must be taken into account. This article attempts to collect all necessary information about visibility and viewshed analysis concerning conventional approaches. Basic viewshed algorithms are described, alternative methods of viewshed analysis are examined and different techniques used in viewshed calculation are referred. All this analysis of algorithms and techniques is accompanied by certain environmental application examples. Further on, factors that influence the accuracy of a viewshed and also possible control procedures are referred. Keywords: visibility, viewshed, GIS, environment, accuracy.Παρουσιάστηκε στο: Fourth International Conference on Management Information Systems, incorporating GIS and Remote Sensin