Remove-OSSIM.md

@@ -340,6 +340,27 @@ Several DEM tiles can be provided at the same time, using the `OpenDEMDirectory`
 
 Geoid are managed with the `GDALOpenVerticalShiftGrid` and `GDALApplyVerticalShiftGrid` function from GDAL API. The former opens a 1D raster grid as a GDAL Datasource, and the latter creates a new datasource from the raster grid (geoid) and a raster (the DEM). Vertical datums (shifts from the reference ellipsoid) are applied on the fly.
 
+All raster that can be opened by gdal can be used as a geoid. In Ossim it was common to use the `egm96.grd` file as geoid, this file cannot be opened by GDAL. However it is still possible to use it by using the following `egm96.grd.hdr` file : 
+
+```
+ENVI
+samples = 1441
+lines   = 721
+bands   = 1
+header offset = 24
+file type = ENVI Standard
+data type = 4
+interleave = bsq
+sensor type = Unknown
+byte order = 1
+wavelength units = Unknown
+map info = {Geographic Lat/Lon, 1, 1,-0.125, 90.125, 0.25, 0.25,WGS-84}
+coordinate system string = {GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]}
+band names = {
+Band 1}
+```
+
+With this file attached, GDAL will be able to read the `egm96.grd` file as a ENVI dataset
 
 #### Initial design