[Qgis-developer] Raster resampling

[Radim Blazek]

Very good,
I appreciate also the side effects like moving rendering methods to
QgsRasterRenderer.

Have you considered a possibility to pass resampling to a driver in
case it supports resampling? At least GDAL supports resampling,
currently used GDALRasterIO does not,  GDALWarp does. GDALWarp was
slow with reprojection, I don't know if resampling is better.

I am especially concerned about reprojection, because reprojection of
images oversampling^2 times bigger may be significantly slower.

Maybe just resampling before reprojection could be considered.

Question for all: is it better to resample images before or after
reprojection? I am thinking especially about dissimilar projections
where resolution ratio between source and destination is not constant
over the extent.

Radim

On Fri, Dec 30, 2011 at 2:58 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi devs,
>
> Recently, I've been working on adding raster resampling to QGIS raster
> (http://www.sourcepole.com/raster-resampling-in-qgis). The changes are in
> the branch 'raster_resampler' of my github clone
> (git://github.com/mhugent/Quantum-GIS.git).
>
> To add resampling in a clean way, I started a bit of refactoring within
> QgsRasterLayer:
>
> - The new abstract class QgsRasterRenderer is added to replace the
> drawingType switch. The method QgsRasterRenderer::draw() is a replacement
> for the methods drawMultiBandColor(), drawMultiBandSingleBandGray(),
> drawPalettedSingleBandColor(). This should move a lot of code out of
> QgsRasterLayer and reduce code complexity. Currently implemented are
> QgsPallettedRasterRenderer, QgsMultibandColorRenderer,
> QgsSingleBandGrayRenderer
> - The functionality of QgsRasterBuffer to draw the raster layer in several
> parts is moved to QgsRasterRenderer base class (same idea of reducing
> complexity in QgsRasterLayer).
> - QgsRasterResampler has two subclasses for now, QgsBilinearRasterResampler
> and QgsCubicRasterResampler (maybe average would be useful as well?)
>
> Any objections or suggestions about this? The code in the branch is mostly
> working, but far from being complete.
> I'm going to be without internet connection the next few days, but hope to
> get the code to a testable state soon.
>
> Regards,
> Marco
>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux&  Open Source Solutions
> Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>
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