I try to conver from ellipsoidal to orthometric heights with arithmetic function. In input raster 2 i put WGS84.img from \peodata\geoid folder.The results are not right. And now i have the question. The input raster 2 is always the same or it is depended on coordinate system? my files which i want to convert are EGSA87/TM87. What i must put in raster 2=N to convert from ellipsoidal to orthometric in EGSA87?