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>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 > > http://www.occamlabs.de > > > _______________________________________________ > gdal-dev mailing list > 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 light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Software Developer
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