esri hillshade algorithm

Calculate hillshade for a digital elevation model (DEM) based on the esri algorithm

Calculate hillshade for a digital elevation model (DEM) based on the algorithm posted on http://edndoc.esri.com/arcobjects/9.2/net/shared/geoprocessing/spatial_analyst_tools/how_hillshade_works.htm
Generated By Felix Hebeler, Dept. of Geography, University Zurich, February 2007.
modified by Andrew Stevens ([e-mail]), 5/04/2007
modified by Wenbin Jiang ([e-mail]), 7/06/2011