I believe I learned how to do this, so to answer my own question: Some of the Band.ReadRaster(...) methods allow to explictly specify the buffer width and height, e.g. [1]. This allows to extract resolutions that differs from the original image (and the overviews).
Best regards, Markus [1] http://gdal.org/java/org/gdal/gdal/Band.html#ReadRaster(int, int, int, int, int, int, int, byte[]) Am 05.09.2013 18:01, schrieb Markus Schneider: > Frank, > > thanks for your reply. Could you (or somebody else) give me a few more > details how to get hold of a raster region with a resolution that is not > defined by an overview? > > Currently, I am able to extract regions from an overview using the > following steps (in Java): > > ... > Dataset dataset = gdal.Open( "dataset.ecw", GA_ReadOnly ); > Band band = dataset.GetRasterBand( ... ); > band = band.GetOverview(...); > band.ReadRaster(x,y, ...) > ... > > Afterwards, I have the raw data values in my array. It works fine for > any overview. > > My problem is that I cannot figure out how to get hold of a Band for a > non-predefined overview. How would I do this? > > Best regards, > Markus > > Am 04.09.2013 18:15, schrieb Frank Warmerdam: >> Markus, >> >> I believe the GDAL ECW driver will pass RasterIO() requests through to >> the ECW SDK to evaluate meaning that there is no constraint based on the >> advertized power-of-two overviews exposed from GDAL and no loss of quality. >> >> Best regards, >> Frank >> >> >> On Wed, Sep 4, 2013 at 6:52 AM, Markus Schneider <schnei...@occamlabs.de >> <mailto:schnei...@occamlabs.de>> wrote: >> >> Dear list, >> >> I am new to programming with GDAL (and to the ECW format). Let me say >> thank you first, because my first experiences have been rather pleasant, >> even if my setup is relatively involved (thanks everybody for providing >> good documentation): >> >> - Ubuntu 12.04 (AMD64) >> - GDAL 1.10.1 (build from source) >> - ECW SDK 5.0 >> - GDAL Java bindings >> >> I successfully created a toy Java class for extracting regions from an >> ECW file. Speed is impressive. >> >> My observations/questions: >> >> - If I understand correctly, ECW files internally do not have such a >> thing as fixed overviews. However, ECW supports extraction of regions >> with specified resolution on-the-fly. Is this correct? >> - GDAL API reports overviews for ECW datasets. Having a first look at >> the code, it seems to generate overview dimensions by subsequently >> dividing height and width by two (until a minium side length of 128 has >> been reached). >> >> Final question: Is it possible to efficiently retrieve (regions of) >> overviews at self-defined scales using the GDAL API? Or do I have to use >> the ECW SDK for that? >> >> Keep up the good work. Thanks for any pointers. >> >> Best regards, >> Markus >> >> -- >> Markus Schneider >> CEO >> >> Occam Labs UG (haftungsbeschränkt) >> Godesberger Allee 139 >> 53175 Bonn, Germany >> >> +49 228 93798874 <tel:%2B49%20228%2093798874> >> >> http://www.occamlabs.de >> >> >> _______________________________________________ >> gdal-dev mailing list >> gdal-dev@lists.osgeo.org <mailto:gdal-dev@lists.osgeo.org> >> http://lists.osgeo.org/mailman/listinfo/gdal-dev >> >> >> >> >> -- >> ---------------------------------------+-------------------------------------- >> I set the clouds in motion - turn up | Frank Warmerdam, >> warmer...@pobox.com <mailto:warmer...@pobox.com> >> light and sound - activate the windows | http://pobox.com/~warmerdam >> and watch the world go round - Rush | Geospatial Software Developer > > > > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev > -- Markus Schneider CEO Occam Labs UG (haftungsbeschränkt) Godesberger Allee 139 53175 Bonn, Germany +49 228 93798874 http://www.occamlabs.de
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