Determining correct format for OFFSETA in Viewshed creation

Discussion created by kemoore1 on Sep 12, 2013
Latest reply on Sep 13, 2013 by curtvprice
I want to create a viewshed for a 20m tall tower.

I have a DEM I created and projected into British National Grid using the project raster function

I have an observer point shapefile also projected in British National Grid. This shapefile has an OFFSETA field. I'm not sure what value to put into this field to represent 20 m. Is it just "20"? The linear measurements for the BNG projection are in metres but the vertical measurements are (apparently) in degrees. What does this mean for my OFFSETA value?

Thanks in advance for your time.