[mapserver-users] Reprojection image quality

[Benoît Andrieu]

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 
  To: 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 
    To: 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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