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Hello Jianping,

	You might want to check out the April 1994 issue of PE&RS.  There is
an article entitled "Digital Analysis of Viewshed Inclusion and Topographic
Features on a Digital Elevation Models"  by Jay Lee.

	It is more theory but does discuss some interesting algorithms...  Also
Jianping Xu had an interesting talk at the recent GRASS conference about r.los
and the problems in the GRASS r.los algorithm...

		Don
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							|
Don Catanzaro						|Phone: (501)-575-6159
Center for Advanced Spatial Technologies 		|Fax:   (501)-575-3846
University of Arkansas                                  |e-mail:
Fayetteville, Arkansas  72701                           |dgc@CAST.uark.edu

	"Part of working for a living is working for a world to live in"
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