Remove-OSSIM.md

@@ -265,18 +265,9 @@ that the DEM management functions are not part of GDAL's
 API. Therefor, it is not possible to access the DEM interpolation as
 expected from the OTB.
 
-The new approach is a suggestion from Even Rouault on GDAL's mailing
-list (see [this
-message](https://lists.osgeo.org/pipermail/gdal-dev/2020-May/052225.html)
-and [that
-one](https://lists.osgeo.org/pipermail/gdal-dev/2020-May/052227.html)). The
-idea is to use the GDALRasterIOExtraArg argument of the RasterIO
-function, by setting bFloatingPointWindowValidity to TRUE and setting
-dfXOff, dfYOff, dfXSize, dfYSize.
+The `otb::DEMHandler` class is a singleton, a reference to the `otb::DEMHandler` object can be obtained via the `GetInstance()` method. 
 
-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.
-
-The new DEMHandler has the same API as its Ossim counterpart, in particular the following methods are provided : 
+The new approach is based on RasterIO. A 2x2 window is extracted around the point of interest, and the height, above ellipsoid or above mean sea level. The following methods are provided: 
 
 * GetHeightAboveEllipsoid():
      * SRTM and geoid both available: dem_value + geoid_offset
@@ -289,6 +280,11 @@ The new DEMHandler has the same API as its Ossim counterpart, in particular the
      * SRTM available, but no geoid: dem_value
      * No SRTM and no geoid available: 0
 
+Several DEM tiles can be provided at the same time, using the `OpenDEMDirectory` method. All raster from the input directory will be opened by GDAL. A mosaic of all DEM tiles is then created as a virtual dataset (vrt).
+
+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.
+
+
 ### Re-implement RPC model
 
 ### Re-implement generic SAR model