WMS and SRS
Daniel Goetz
madprof at GMX.CH
Fri Jul 28 04:44:23 EDT 2006
Hi Bart,
thank you for your reply.
But the extent in the mapfile is the same as the BBOX-values in the WMS-request. And the SIZE in the MAP-object of the mapfile is the same as in WIDTH+HEIGHT in the WMS-request. And nevertheless the two "reprojected" maps differ in appearance (distortion).
But you are right. I should check that the BBOX and the WIDTH/HEIGHT-values have the same proportion. Do I also have to check wheter SIZE and EXTENT in the MAP-object have the same proportions as well? And how can I measure the distance between the vertices of my EXTENT and the distance between the vertices of my BBOX? Any suggestion?
Thank you for your help and hopefully your further ideas. Thank you.
regards
Daniel
-------- Original-Nachricht --------
Datum: Fri, 28 Jul 2006 10:26:38 +0200
Von: "Bart van den Eijnden (OSGIS)" <bartvde at xs4all.nl>
An: Daniel Goetz <madprof at GMX.CH>
Betreff: Re: [UMN_MAPSERVER-USERS] WMS and SRS
> 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&version=1.1.1&service=WMS&request=GetLegendGraphic&layer=VIEW_RWG_TBS&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
> >>
> >>
> >>--
> >>
> >>
> >>Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen!
> >>Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer
> >>
> >>
> >
> >
> >
>
>
> --
> Bart van den Eijnden
> OSGIS, Open Source GIS
> http://www.osgis.nl
>
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