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.
