raster : bad quality in output

[Didrik Pinte]

Le jeudi 07 avril 2005 à 12:00 -0400, Ed McNierney a écrit :
> Didrik -
> 
> What I meant was, "are all the pixels in the relevant portion of the input image used exactly once to produce one pixel in the output image"?  That is, is the output image a rectangular piece of the original input image at the same size, or is it "zoomed in" or "zoomed out"?
> 
> Unfortunately, scale ratios are meaningless for digital images without also specifying the output resolution in pixels per physical unit (inch, cm, etc.).  It is very likely that the scale ratios of your source images refer to a different resolution than the default 72 pixels per inch that MapServer uses.
> 
> Can you find out what the intended output resolution of your rasters is?  For example, if I tell you that a raster is at 1/50000 scale, I am saying that one cm on the image equals 5 km on the ground.  But that obviously depends on the physical resolution at which the image is viewed - if I am viewing it at 50 pixels per cm, then 50 pixels in the image equals 5 km on the gorund.  But if I'm viewing it at 100 pixels per cm, then 100 pixels in the image equals 5 km on the ground.  You need to know the intended viewing resolution in order to answer this question.
> 
> If the rasters are scanned images of printed maps, this value would normally be the scan resolution.
> 
>      - Ed

Great, I received the information about the "intented viewing
resolution".

It was 32 points per cm, giving 81.28 dpi ! 

I've set the RESOLUTION parameter to 81.28 and it renders perfectly when
using scale near the raster scale !

Thank you very much for the information (and the explanation too).

Didrik
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
Url : http://lists.osgeo.org/pipermail/mapserver-users/attachments/20050408/4761abb2/attachment.bin