[mapserver-users] Reprojection image quality

[Brent Fraser]

Benoît,

  Try some of the other "-r" options such as "cubic"

Brent Fraser


Benoît Andrieu wrote:
> Hi all !
>  
> Once again, I'm here !!
>  
> So my results :
> - tps has no effects at all,
>  
> - generating a merge with gdalwarp on a small number of files
>      or
> generating a merge with gdalwarp on all the files plus specifying the 
> same extent of the small number of files
> does not give me the same result.
> In the first case, the image is great with no artefacts, in the second 
> case the image is not good at all with duplicated groups of pixels along 
> vertical and horizontal lines. One could see the results on the same 
> files as previously : 
> http://benoit.andrieu.free.fr/mapserver/Clipboard02.png
>  
> Has anyone any tips for me ?? ^^
>  
> Benoît
>  
> 
>     ----- Original Message -----
>     *From:* Benoît Andrieu <mailto:bea at ixsea.com>
>     *To:* mapserver-users at lists.osgeo.org
>     <mailto:mapserver-users at lists.osgeo.org>
>     *Sent:* Tuesday, September 23, 2008 10:33 AM
>     *Subject:* Re: [mapserver-users] Reprojection image quality
> 
>     Hi all !
>      
>     I am trying to play with the parameters of gdalwarp.
>      
>     It seems that the tps option gives better output result than
>     omitting this parameter.
>     I just tried on a subset of my data and the resulting picture is
>     very nice comparing to the previous. Right now, I am trying it on
>     the whole dataset.
>      
>     By the way, could someone explain what it really does ?
>     Is this a better/different algorithm ?
>      
>     -tps:
>         Force use of thin plate spline transformer based on available GCPs. 
>      
>     Benoît
>      
> 
>         ----- Original Message -----
>         *From:* Benoît Andrieu <mailto:bea at ixsea.com>
>         *To:* mapserver-users at lists.osgeo.org
>         <mailto:mapserver-users at lists.osgeo.org>
>         *Sent:* Tuesday, September 23, 2008 9:24 AM
>         *Subject:* [mapserver-users] Reprojection image quality
> 
>         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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