Global Mapper v24.0

Creating WAsP roughness map from raster data

squaredeal Global Mapper User
I have an elevation raster grid in global mapper and would like to use this to create a WAsP roughness map using the elevation values as roughness.

I have created areas of equal elevation from the raster grid and each area has an "ELEVATION" attribute.

How can I add the required "ROUGH_L" and "ROUGH_R" attributes and set the correct values for all area features (doing this manually would take too long as there are a large number of area features)?