[gdal-dev] Change Resampling method

Frank Warmerdam warmerdam at pobox.com
Wed Mar 10 15:31:12 EST 2010

Paul Meems wrote:
> We're using GDAL in MapWindow GIS and we're very happy about it.
> Thanks for this great library.
> Currently we have problems displaying png files representing only a few 
> lines.
> The lines show up very stippled. Pixels are missing.
> Reading this article, this seems 'by design':
> http://n2.nabble.com/Change-Resampling-method-td3827881.html
> This is not tolerable for us so we will try and make a custom method to 
> resample using lanscoz.
> Before we dig in to this I want to know is others are working on this as 
> well and/or have some tips&tricks.
> No need to reinvent the wheel again, right ;)


There is a lanscoz resampler built into the GDAL warper, but I'm not
convinced this would be a good idea for general use by a display engine.

I'd suggest, in cases like this, to use RasterIO() to load a closer to
the underlying resolution and do the rest of the downsampling yourself
using lanscoz or other methods.

In a web mapping application built on MapServer using black and white
scanline linework drawings, we found just using averaging for downsamping
gave good results in preserving the linework in a sort of anti-aliased
fashion.  So you might not need anything to fancy for the resampling.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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