[gdal-dev] Distinguish between no DTED data and actual DTED elevation of 0

[LEGGE Melvin]

Hi

I am a relative newbie to GIS programming so forgive me if I use the wrong terminology or don't state my problem in the most efficient GIS terms. Anyway, I have inherited a project written by an actual GIS person who is no longer with the company.

The DTED data consists of 4 GDalDatasets with actual DTED elevation data not reaching the boundaries of GDalDatasets - i.e., GDalDatasets are bigger than the actual DTED data.  Our program reads the elevation data along a bearing line from a given point to some requested distance, at regular intervals, by repeatedly calling GDALRasterBand->RasterIO for a specified distance.  What I am seeing is that elevation values of 0 are returned for points between the end of the DTED data and the end of the tile.

Is there any way I can distinguish between the situation above and an actual elevation of 0?  RasterIO always returns CE_None and the returned value is never equal to noDataValue.

Thanks
Mel




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