ELLIPSOID = STO@b POP STO@a POP RCL@a 2 POW Y COSD MUL 2 POW RCL@b 2 POW Y SIND MUL 2 POW ADD RCL@a Y COSD MUL 2 POW RCL@b Y SIND MUL 2 POW ADD DIV SQRT
gmt grdmath -Rg -I1 6378137.0 6356752.3142 ELLIPSOID = my.grd
That would be fantastic for any “planetary” mapping.