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Viewshed analysis based on the regular grid digital elevation model (DEM) is one of the basic functions of geographic information systems. Traditional viewshed analysis algorithms are mainly carried out in a geospatial coordinate system, that create complexities when it is necessary to accurately express a perspective relationship. Moreover, it can only reduce the amount of calculation by using approximation methods, which result in decreased accuracy. We found that the error ratio of approximation algorithms is low but uneven and thereby highly likely to result in continuous area visibility errors. Despite the quality of DEM data having improved significantly in the last decade, traditional approximation algorithms have been unable to take full advantage of the improved data. Finding a fast and accurate algorithm has therefore become an urgent task. This study takes a new perspective to solve this problem by establishing a ‘proximity-direction-elevation’ (PDE) coordinate system and proposing a PDE spatial reference line (PDERL) algorithm within it. Many experiments prove that the accuracy of PDERL is the same as the R3 algorithm and its speed is about half that of the XDraw and reference plane algorithms, but much faster than R3. Due to the speed of PDERL, it is now possible and practical to do an accurate large-area DEM-based viewshed analysis.

PDERL: an accurate and fast algorithm with a novel perspective on solving the old viewshed analysis problem