[gdal-dev] Extracting (arbitrary?) overviews from ECW file

[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 <schneider at 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
>
>
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