[Gdal-dev] Does gdalinfo Bounding Box Information really match DTED / SRTM ?

[Michael84]

Thank you very much. Is there no GDAL function to have a "point" view of
GDALDataSet ?


Frank Warmerdam-2 wrote:
> 
> Michael84 wrote:
>> I use gdalinfo to extract bounding box information of DTED L0&L1 (dt0,
>> dt1)
>> as well as SRTM (hgt over bil+hdr+proj solution) data.
>> In both cases the reported corner points are not integer values as
>> supposed. 
>> 
>> Corner Coordinates: (DTED)
>> Upper Left  (  -0.0041667,  49.0041667) (  0d 0'15.00"W, 49d 0'15.00"N)
>> Lower Left  (  -0.0041667,  47.9958333) (  0d 0'15.00"W, 47d59'45.00"N)
>> Upper Right (   1.0041667,  49.0041667) (  1d 0'15.00"E, 49d 0'15.00"N)
>> Lower Right (   1.0041667,  47.9958333) (  1d 0'15.00"E, 47d59'45.00"N)
>> Center      (   0.5000000,  48.5000000) (  0d30'0.00"E, 48d30'0.00"N)
>> 
>> Is this is a roundig bug of gdal or are the data sources just coded like
>> this ?
> 
> Michael,
> 
> GDAL treats pixels are representing an area, and the bounds of a raster
> are the bounds of the outer edges of the pixel region.
> 
> DTEDs however are normally thought of as samples at points (with a pixel
> sometimes drawn around that point to represent it).  When thought of as
> point data DTED corners are right on 1 degree cell boundaries.
> 
> So this is the class "pixel as area" vs. "pixel as point" discrepency
> which results in an off-by-one-half-pixel difference under various
> circumstances.
> 
> So, there is no bug, only differences in interpretation of what the
> bounds of a raster are.
> 
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
> 
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> 

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