Calculating Topographic Exposure with Raster Calculator

Discussion created by mtobiasz on Mar 14, 2014
Latest reply on Mar 14, 2014 by Hornbydd
I need you help trying to calculate Topographic Exposure (TOPEX) on a DEM in ArcGIS.  I am trying to figure out wind exposure on a DEM with 25m cells.
There is a great blog post where someone explains how to do it but he uses GRASS. thought I would be able to put the same equation into ArcGIS Raster Calculator but it says the equation is invalid. I've tried playing with it as much as I can but I can't seem to make it work.

His first equation is:    r.mapcalc incl4north = "atan(((dem - dem[4,0])) / ((25 * 4)))"
And then he goes on to string a bunch of them together
Does anyone know how the equation should appear in Raster Calculator in either ArcGIS or QGIS?
I am super grateful for any assistant that anyone could provide