[mapserver-users] mapserver wms: srs problem

[Matthew Pettis]

Hi All,

I'm posting further findings and observations.  I made a simple
mapfile and dumped the shape information to a .shp file.  I have made
a .zip file with all of the components to verify what I will be
saying, and will provided it upon request to individuals (don't want
to pollute inboxes on the listserv indiscriminantly).

First, I have discovered that when I render the shapefile NOT as a
WMS, but just with a url like:

http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\tb\ex.map&mode=map

the coords are unprojected, and I get the expected (tall and skinny)
map of MN.  When I call mapserver as a WMS (with epsg:26915), like:

http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\tb\ex.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&LAYERS=state&BBOX=184056.505,4809728.25,767381.245,5478975.75&SRS=EPSG:26915&format=image/png&width=800&height=600

then I get a map, but the map stretches to the dimensions I set the
image 'height' and 'width' parameters to.  This does not happen with
the non-WMS request.

So the point is, my WMS map calls stretch as a function of the image
width and height (which is how it is called for openlayers).  If I
want the unprojected map via WMS (that doesn't stretch based on the
tile image dimensions), how do I configure my WMS url, or .map file
(particularly for openlayers)?

Thanks again for everybody's help,
Matt

On Tue, Jun 10, 2008 at 11:26 AM, Barend Kobben <kobben at itc.nl> wrote:
> Hi,
>
> It looks like your mixing up several things that shouldn't be mixed:
>
> 1)
> http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\ol\wms.map&SE
> RVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities
> ...is a valid WMS GetCapabilities request. It might result in a valid WMS
> response (although I cannot test this as I obviously  do not have the same
> localhost as you...)
>
> However:
> http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\ol\wms.map&mo
> de=map
> ...is a non-WMS request, it uses the 'old' MapServer CGI mode, not the OGC
> standardised WMS interface. To get a map the "WMS way" you'd request
> something like:
> http://localhost/cgi-bin/mapserv.exe?map=C:\ms4w\Apache\htdocs\ol\wms.map&m&
> SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&LAYERS=aLayer&BBOX=1,2,3,4&
> SRS=EPSG:4326&format=image/gif
>
> 2) next, you advertise your data to be in lat-lon on the WGS 84 (PROJECTION
> init=epsg:4326), but you proclaim the EXTENT of the data to be in meters or
> some other projected unit:
> EXTENT      184056.505 4809728.25 767381.245 5478975.75
> This obviously are not lat-lon degrees (which have a max extent of
> -180,180,-90,90)... Now MS will be really confused! "Hmmmm, this client
> wants lat-lon data that stretches over the whole of the universe..." :-)
>
> 3) you then advertise the WMS to be able to deliver data in a non-projected
> and a projected SRS:
>  "wms_srs"             "EPSG:4326 EPSG:26915"
> Which is fine, but you do it again for the LAYER, which I think is
> superfluous.
>
> 4) You do NOT tell the WMS what SRS the data originally is in. There is no
> PROJECTION object in the LAYER, which in some case might lead to MapServer
> trying to find out for itself, BUT NOT in the Postgis case you have. A
> connection to PostGIS in itself needs to be told which projection to fetch
> the data in (because PosGIS can reproject if necessary). One of the ways of
> doing that is to make the DATA statement a bit more elaborate than
>  "the_geom from shp_state", instead use
>  DATA   "the_geom from shp_state using unique <your_primary_key> using
> srid=26915"
>
> Hope this helps...
>
> --
> Barend Köbben
> International Institute for Geo-Information
> Sciences and Earth Observation (ITC)
> PO Box 6
> 7500AA Enschede, The Netherlands
> +31 (0)53 4874253
>
> International Institute for Geo-Information Science and Earth Observation (ITC)
> Chamber of Commerce: 410 27 560
>
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