WMS and SRS

Fri Jul 28 04:26:38 EDT 2006

Hi Daniel,

please remember that if the ratio of your bbox and the ratio of your 
width versus height in pixels, differs, the map will be stretched. That 
could explain some of the behaviour. You need to make sure that the 
values in your WMS request have the same ratio. I don't know if this is 
the problem, but it could be a cause.

Proj.4 has a utility to reproject. The proj utilities also come with 
MS4W. See also:

http://proj.maptools.org/man_cs2cs.html

Best regards,
Bart

Daniel Goetz wrote:

>Hi,
>
>thank you Frank, Trond and Ed for your help. I tried to use reporjected coordinates as BBOX-values in my "new" WMS-GetMap-request (SRS=WPSG:4326) and it works now. I got the new reprojected coordinates out of the GetCapabilities document (I took them out of the LatLonBoundingBox paragraph in the GetCapabilities document):
>
><Layer queryable="1" opaque="0" cascaded="0">
>        <Name>VIEW_RWG_TBS</Name>
>        <Title>RWG_TM_NR</Title>
>        <SRS>EPSG:31468</SRS>
>        <SRS>EPSG:4326</SRS>
>        <LatLonBoundingBox minx="10.9905" miny="49.3319" maxx="11.2852" maxy="49.5441" />
>        <BoundingBox SRS="EPSG:31468"
>                    minx="4.42695e+006" miny="5.46647e+006" maxx="4.44806e+006" maxy="5.48982e+006" />
>        <Style>
>          <Name>default</Name>
>          <Title>default</Title>
>          <LegendURL width="20" height="10">
>             <Format>image/png</Format>
>             <OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink" xlink:type="simple" xlink:href="http://10.65.112.50/cgi-bin/mapserv.exe?map=/ms4w/apache/htdocs/WMS/WMS_BRWK.map&amp;version=1.1.1&amp;service=WMS&amp;request=GetLegendGraphic&amp;layer=VIEW_RWG_TBS&amp;format=image/png"/>
>          </LegendURL>
>        </Style>
>    </Layer>
>
>
>But I have two further questions:
>
>When I do a WMS-GetMap-request in the "new" SRS (EPSG:4326) the map maserver sends back does not vary form the map mapserver generates when sending a GetMap-request in the "original" SRS (EPSG:31468). I mean there is no deformation/distortion noticeable. But when I do a "normal" mapserver mode=browse-request in my simple pan and zoom template and tell mapserver to reproject the data in EPSG:4326 (I do that by putting the PROJECTION-object in the MAP-object of the .map-file to "init=epsg:4326" while the PROJECTION-objects in the LAYER-objects are still in the "origninal" "init=epsg:31468" projection. Of course I  change the EXTENT-parameters in the .map-file too. Am I doing right?) the returned map looks different from the map genereated using the "original" projection. I mean that the reprojected map using mode=browse looks deformed/distorted compared to the "original" not reprojected map.
>
>The question is now: Why do the two maps (the reprojected one I get from the WMS-GetMap-request and the reprojected map I get by a mode=browse request) differ in their appearence (distortion) although I tell mapserver in both cases to reproject the map to "epsg:4326"?
>
>The secoond question is: As mentioned I got the "new" reprojeted coordinates for BBOX-values out of the GetCapabilities document. But is there a program that could do coordinate transformation for me, so that I am able to transform "epsg:31468" coordinates to "epsg:4326" coordinates?
>
>
>OK, that's it. Thak you again for your helpful hints. And would be very nice of you if you could help me further on with my problems/questions elucidated in this email. Thank you so much.
>
>
>regards
>
>Daniel
>
>
>-------- Original-Nachricht --------
>Datum: Thu, 27 Jul 2006 09:22:21 -0400
>Von: Ed McNierney <ed at TOPOZONE.COM>
>An: MAPSERVER-USERS at LISTS.UMN.EDU
>Betreff: Re: [UMN_MAPSERVER-USERS] WMS and SRS
>
>  
>
>>Daniel -
>>
>>I think Frank's theory is likely to be correct, and that there is a
>>problem with the BBOX coordinates used in your new request.  It sounds like the
>>changes you made are fine, although I think it is not necessary to add all
>>supported SRS systems to the metadata for each layer - just the MAP-level
>>metadata should be all you need to do.
>>
>>Can you post the SRS= and BBOX= parameters you are using in your original
>>epsg:31468 request and in the new epsg:4326 requests?
>>
>>	- Ed
>>
>>Ed McNierney
>>President and Chief Mapmaker
>>TopoZone.com / Maps a la carte, Inc.
>>73 Princeton Street, Suite 305
>>North Chelmsford, MA  01863
>>ed at topozone.com
>>(978) 251-4242  
>>
>>-----Original Message-----
>>From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
>>Behalf Of Daniel Goetz
>>Sent: Thursday, July 27, 2006 3:05 AM
>>To: MAPSERVER-USERS at LISTS.UMN.EDU
>>Subject: [UMN_MAPSERVER-USERS] WMS and SRS
>>
>>Hi coummunity,
>>
>>I built up a littel WMS-server with umn-mapserver (local installation;
>>ms4w 2.1). The "original" projection of the single Layers is alway epsg:31468
>>(these are cartesian Gauß-Krüger-coordiantes). So I set the
>>PORJECTION-object of each LAYER and in the MAP-object to "init=epsg:31468". In the
>>METADATA of the MAP-object as well as in the single LAYER-objects I defined
>>"wms_srs" as "EPSG:31468" as well. For testing purpose I did some
>>WMS-GetMap-Requests with "SRS=EPSG:31468" and everything went fine.
>>
>>But now I want to make my WMS-service more interchangeable, so I want to
>>define some more SRSs in that the WMS should be able to be displayed. I want
>>to make it possible to "transform" (don't know the exact word in english)
>>the WMS from its original Projection to another SRS (e.g. WGS 84;
>>EPSG:4326). In my opinion this should be possible by adding another epsg-code to the
>>METADATA. So my METADATA (both in the MAP and in the LAYERs-objects) look
>>like this: "wms_srs" "EPSG:31468 EPSG:4326".
>>
>>But now every time I change the SRS block in my WMS-GetMap-request from
>>"SRS=EPSG:31468" to "SRS=EPSG:4326" mapserver returns a blank image. I even
>>tried to set the BBOX to latlon-coordinates when using "SRS=EPSG:4326" but
>>even this failed. I also testes other SRSs (both geographic ones and real
>>projections) but with no success.
>>
>>Could anybody please give me some help or hints what to do and what went
>>wrong and why did this happen? I would be very glad and thankful. Thank you
>>so much.
>>
>>
>>regards
>>
>>
>>Daniel
>>
>>
>>-- 
>>
>>
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>>    
>>
>
>  
>

-- 
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl