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

[Markus Schneider]

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 <schneider at occamlabs.de
>> <mailto: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 <tel:%2B49%20228%2093798874>
>>
>>     http://www.occamlabs.de
>>
>>
>>     _______________________________________________
>>     gdal-dev mailing list
>>     gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org>
>>     http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>>
>>
>>
>> -- 
>> ---------------------------------------+--------------------------------------
>> I set the clouds in motion - turn up   | Frank Warmerdam,
>> warmerdam at pobox.com <mailto:warmerdam at 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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-- 
Markus Schneider
CEO

Occam Labs UG (haftungsbeschränkt)
Godesberger Allee 139
53175 Bonn, Germany

+49 228 93798874

http://www.occamlabs.de

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