1. At this stage it is assumed you have created a GRASS project in UTM projection and imported the DEM for your area in that project.

2. Create a new GRASS project in the same database as your UTM project.
   1. Let's assume the name is AREA_LL and mapset PERMANENT.
   2. The projection needs to be Lat/Lon, the area boundaries are not important.
   3. The resolution can also by any for now.
   4. The datum should wgs84 and parameter should be 1.

2. Once you have entered the AREA_LL project, import the elevation spheroid as below;

      r.in.ascii input=~arsf/dems/geoid-spheroid/ww15mgh.grd output=wwgsg
   

3. Now you can exist AREA_LL, go back to your UTM project
   1. Import/Re-project the elevation spheroid as below;

         r.proj -n input=wwgsg location=AREA_LL mapset=PERMANENT output=wwgsgUTM
      

   2. Now elevated the DEM by adding the spheroid;

         r.mapcalculator amap=yourDEMmap bmap=wwgsgUTM formula=A+B outfile=yourelevatedDEMmap help=-
      

4. Process is complete!