[Qgis-user] WMS problem - QGIS 1.0 prev 2

[Marco Hugentobler]

Hi Thomas

The WMS specification for WMS 1.3 specifies that for epsg geographical 
coordinate systems, the order of the bounding box parameters is latMin, 
longMin, latMax, longMax. For other crs, it is xmin, ymin, xmax, ymax.
In contrast, WMS 1.1.1 used longMin, latMin, longMax, latMax also for 
geographic CRS.

Therefore, QGIS switches latitudes and longitudes for epsg 4326 (and other 
geographical CRS) if the server states that it supports WMS 1.3.

I think the geoportal server does not consider the mentioned change between 
WMS 1.1.1 and WMS 1.3.

Marco




From the 1.3. implementation specification 
(http://portal.opengeospatial.org/files/?artifact_id=14416), page 15 and 
following:

Coordinates shall be listed in the order defined by the CRS and shall be mapped 
appropriately to the Map CS i
and j axes, swapping axis order as needed during the projection operation. 
Many projected coordinate reference
systems have an axis and coordinate order other than easting, northing. For 
example, the Uniform Coordinate
System used in Finland (EPSG:2393) orders northing before easting. EPSG 
geographic coordinate reference
systems follow ISO 6709 and always list latitude before longitude.


and later they give an example for BBOX:

EXAMPLE 2
A <BoundingBox> representing the entire Earth in the EPSG:4326 Layer CRS would 
be written as
<BoundingBox CRS="EPSG:4326" minx="-90" miny="-180" maxx="90" maxy="180">.
A BBOX parameter requesting a map of the entire Earth would be written in this 
CRS as
BBOX=-90,-180,90,180.







On Tuesday 25 November 2008 19:52:14 Tomasz Suchan wrote:
> Hi All,
> I have a problem with WMS requests... I'm trying to add WMS layer to my
> project. All goes well with http://wms.jpl.nasa.gov/wms.cgi server, but I
> have problems when I try to add
> http://maps.geoportal.gov.pl/WMS_ORTO/WMService.aspx - I can see only white
> background of the layer with server's watermark on it...
> I have figured out what's wrong but unfortunately I have no clue how to fix
> that. The request from QGIS is as follows:
>
> http://maps.geoportal.gov.pl/WMS_ORTO/WMService.aspx?SERVICE=WMS&VERSION=1.
>3.0&REQUEST=GetMap&BBOX=50.304627,16.799312,50.304822,16.799668&CRS=EPSG:432
>6&WIDTH=1052&HEIGHT=576&LAYERS=ORTOFOTO&STYLES=&FORMAT=image/jpeg
>
> But, server ends me the proper map when I switch latitudes and longitudes
> as below:
> http://maps.geoportal.gov.pl/WMS_ORTO/WMService.aspx?SERVICE=WMS&VERSION=1.
>3.0&REQUEST=GetMap&BBOX=16.799312,50.304627,16.799668,50.304822&CRS=EPSG:432
>6&WIDTH=1052&HEIGHT=576&LAYERS=ORTOFOTO&STYLES=&FORMAT=image/jpeg
>
> Thanks for any help, Tom

-- 
Dr. Marco Hugentobler
Institute of Cartography
ETH Zurich
Technical Advisor QGIS Project Steering Committee