Mapserver response

[Frank Warmerdam]

On 5/13/05, Norman Barker <nbarker at rsinc.com> wrote:
> Hi,
> 
> what is the condition that cause MapServer to either retrieve the file and send it back to the user, or to resample the file?  Looking at the socket if MapServer doesn't really do anything to the file then the response (tiff in my case) is sent back as text, but if it does do anything then the response is sent back with a GET header and content-type set, and the reponse-body.

Norman, 

First, in normal use MapServer never sends back source raster files
unaltered.  Even if you are serving from a jpeg file, and request the image
at exactly full resolution, you still won't get the original file. 
Instead it will
be decompressed, resampled (even if only 1:1 nearest neighbour),
rendered in memory and then written out and recompressed to JPEG 
to be returned to the client. 

Perhaps you are wondering when the simple "zoom" resampling is
used as opposed to the more generic warper resampling used for
reprojection (and odd pixel aspect ratios)?  These are certainly 
quite distinct modes.  The warper resampling kicks in when the
layer and map projections differ or if the requested result will have
non-square pixels. 

> My reason for asking is find some way of getting the data back unaltered as work around to a bug with resampling.

Is this the problem in bug report 1183?  

> I guess the response mechanism in MapServer is the same for the WMS and WCS.

Essentially, yes.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent