[mapserver-users] Reprojection image quality

[Paul Ramsey]

Try adding lines like

PROCESSING "RESAMPLE=BILINEAR"
PROCESSING "OVERSAMPLE_RATIO=1.5"

to your image layer in the map file.

Move the oversample ratio up and down by increments of 0.1. Find
something you like. If speed isn't an issue, change resample to
AVERAGE and comment out the oversample line.

p.

On Tue, Sep 23, 2008 at 12:24 AM, Benoît Andrieu <bea at ixsea.com> wrote:
> Hello guys !
>
> I currently have some problems in the quality of the images produced by
> GDAL/Mapserver.
>
> We are using MapServer to serve raster imagery to NASA Worldwind.
> Our files are in UTM and Worldwind needs WGS84 images so we do reprojection
> on the fly.
> Using this, we can clearly see image quality artefacts between Worldwind
> (using WGS84, no choice) and a custom internal tool (showing original data).
>
> I can reproduce the problem using gdalwarp tool using a very simple command
> line :
> gdalwarp -multi -t_srs EPSG:4326 -srcnodata 0 -dstnodata 0 -r near
> %FileSrc%/*_p_*8bit.tif %FileDest%
>
> You can see the result on
> http://benoit.andrieu.free.fr/mapserver/Clipboard02.png : on the right, the
> original image and on the left, the resulting output.
>
> I suspect that using some others settings, I could improve the quality on
> gdalwarp's output in a first time and on mapserver's output in a second time
> but I don't know where to start...
>
> So if anyone could help or suggest anything, he will be welcome !!!
>
> Thanks in advance,
>
> Benoît
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