Viewshed with elevation of Geographic Coordinate System

Discussion created by tubakumbara on Apr 21, 2010
Latest reply on Apr 28, 2011 by rachaelh3uk
I have a problem . I am trying to perform viewshed analysis with GCS elevation data. My elevation data includes all world. The elevation values are all in meters. And I have observers shapefile with the same coordinate system of elevation layer. But I want to restrict the area in which the viewshed will be performed. In observers attribute  table I added the fields RADIUS1 and RADIUS2 but I don't know exactly what value of RADIUS2 can be given. Because the coordinate system is in lat and lon . Whatever I give, always the result layer includes only 0s (NOT VISIBLE). But when I clip the elevation data and I omit the RADIUS fields, the result layer is OK.
Must linear unit take place in elevation data?If so this means that the elevation data must be in Projected Coordinate System when working with RADIUS values.
Could you please help me.Am I doing something wrong? Is there anything I must take into consideration?