[gdal-dev] Interpretation of DTED elevation data

[Even Rouault]

Selon AlexRNL <alex.barfety at signalis.com>:

> Hi everyone!
>
>
> I have been trying to extract elevation data from a DTED file using GDAL (in
> Java). The file being loaded is of level 0 precision and seems to be correct
> as an import into Global Mapper is rendering the expected result.
>
>
> I managed to retrieve the image data but I don't know to transform those
> values into a altitude in meters.
>
>
> According to the DTED format specification, the elevation values are
> supposed to be two-bytes integer in meters. But, when using the
> http://www.gdal.org/java/org/gdal/gdal/Band.html#ReadRaster_Direct(int, int,
> int, int, int, int, int, java.nio.ByteBuffer) ReadRaster_Direct method, the
> buffer retrieved is supposed to be composed of Int16 number but when i'm
> converting the raw data (bytes) into a short array i'm getting all sorts of
> value which doesn't make a lot of sense. The range of the elevation is
> spanning from 1 to 65286!
>
>
> Is there a conversion that i'm missing? How do I get the meter value from
> the raster returned by GDAL?

You should make sure to request with buf_type = gdalconst.GDT_Int16. Then
iterating the buffer with getShort() should deliver the expected values.

Otherwise use the version of ReadRaster() that accepts a short[]. That will be
simpler to use.

The benefit of using ByteBuffer instead standard Java arrays only appears with
*huge* arrays

>
>
> I've been searching for a while but it doesn't seem like anyone has that
> kind of problem...
>
>
> Thanks in advance for any information that may help me :)
>
> Alex.
>
> --
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