An improved algorithm for computing viewshed based on reference planes

Although the algorithm for computing viewshed based on reference planes (the RP viewshed algorithm) doesn\´t need to use DEM interpolation method and is more efficient than the R3 algorithm. However, its result in the terrain of the "peaks and valleys" still has a big difference with the result of the R3 algorithm. For one thing, this paper deeply analyzes the defects of the RP compared with the R3 viewshed algorithm in the terrain of the "peaks and valleys". For another, this paper proposes an improved algorithm for the RP viewshed algorithm. This improved algorithm not only has the nearly same efficiency with the RP algorithm, but also has small difference with R3 in the terrain of the "peaks and valleys".