New DEM handler without OSSIM.
Sub issue of #1506 remove OSSIM.
otb::DEMHandler class is an adaptater class for OSSIM DEMs. The objective is to refactor this class to use GDAL instead.
As @jmichel explains in comments, the RPC transform class in GDAL accepts a path to a DEM file, which is then opened and used internally by the RPC class. The first idea was to encapsulate this class in OTB. But after investigations, it appears 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 and that one). The idea is to use the GDALRasterIOExtraArg argument of the RasterIO function, by setting bFloatingPointWindowValidity to TRUE and setting dfXOff, dfYOff, dfXSize, dfYSize.
This work will be decomposed in 2 steps:
- make a prototype for the DEM interpolation directly in GDAL's code, to assess the feasibility of the approach.
implement the new