[OpenLayers-Users] Context Documents - WMC.html example

Tue Jul 29 14:13:58 EDT 2008

Hi Joanne,

I use it with a different projection than EPSG:4326, but I have my map 
constructed beforehand and merge the context layers back into an 
existing map object. Also because it is hard for OL to guess what set of 
resolutions is a good match for your projection.

If I load the first document you sent, the units on the map (map.units) 
are still degrees, but I assume EPSG:42304 is meters or not?

Install Firebug, and see what WMS requests OL is sending, for instance 
now I am getting a BBOX which won't result in anything ofcourse.

&BBOX=339480,1962400,339840,1962760
or 339840,1962040,340200,1962400

My first guess would be the units. Otherwise check the set of 
resolutions/scales.

Best regards,
Bart

McGraw, Joanne wrote:
> Hello everyone,
>
> I have been trying to load a context document through the OpenLayers
> wmc.html example for a couple of days now to no avail. I am using
> OpenLayers 2.6 and MapServer 5.0.2.
>
> The context document I would like to display is included below (the
> first one); note the BoundingBox and Layer SRS and Extents, including
> the layer's ol:maxExtent and ol:units. That first context document does
> not display anything in the map in the wmc.html page but there is no
> suggestion that a problem occurred anywhere along the way. The browser
> "waits" for atlas.gc.ca and is eventually "Done", but no data displays.
>
> The second context document below does display the layer defined in the
> wmc.html map. The only things different between the two context
> documents are related to the SRS and extents. In the second context
> document, I use lat/long values and don't bother trying to set the
> ol:maxExtents and ol:units specifically. I just leave them at the
> defaults.
>
> When I look at the results of the GetCapabilities request to the
> atlaswms_en service, the definition for the "can_1m_bound" layer
> suggests I should be able to get the map using the EPSG:42304
> projection. For verification, the GetCapabilities xml can be obtained
> with:
> http://atlas.gc.ca/cgi-bin/atlaswms_en?service=WMS&version=1.1.1&request
> =getCapabilities 
>
> Are context documents using projections and extents that are not
> lat/long supported? I can't find any documentation suggesting that this
> is the case and that there is a problem with what I am trying to do.
> Assuming other SRS besides EPSG:4326 are supported, can anyone suggest
> where I am going wrong below?
>
> Cheers,
> jtm
>
> ------------------------------------------------------------------------
> --------
>
> <ViewContext xmlns="http://www.opengis.net/context" version="1.1.0"
> id="atlas_en" xsi:schemaLocation="http://www.opengis.net/context
> http://schemas.opengis.net/context/1.1.0/context.xsd"
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
> <General>
>     <Window width="512" height="256"/>
>     <BoundingBox SRS="EPSG:42304" minx="-2700000" miny="-725000"
> maxx="3380000" maxy="4650000"/>
>     <Title>NLWIS Map</Title>
>         <Extension>
>             <ol:maxExtent xmlns:ol="http://openlayers.org/context"
> minx="-2750000" miny="-900000" maxx="3250000" maxy="3900000"/>
>         </Extension>
>   </General>
>   <LayerList>
>         <Layer queryable="1" hidden="0">
>             <Server service="OGC:WMS" version="1.1.1" title="National
> Atlas WMS">
>                 <OnlineResource xlink:type="simple"
> xmlns:xlink="http://www.w3.org/1999/xlink"
> xlink:href="http://atlas.gc.ca/cgi-bin/atlaswms_en?"/>
>             </Server>
>             <Name>can_1m_bound</Name>
>             <Title>Boundaries (1:1 000 000)</Title>
>             <SRS>EPSG:42304</SRS>
>             <Extension>
>                 <ol:maxExtent xmlns:ol="http://openlayers.org/context"
> minx="-2700000" miny="-725000" maxx="3380000" maxy="4650000"/>
>                 <ol:units
> xmlns:ol="http://openlayers.org/context">meters</ol:units>
>             </Extension>
>         </Layer>
>   </LayerList>
> </ViewContext>
>
> ------------------------------------------------------------------------
> --------
>
> <ViewContext xmlns="http://www.opengis.net/context" version="1.1.0"
> id="atlas_en" xsi:schemaLocation="http://www.opengis.net/context
> http://schemas.opengis.net/context/1.1.0/context.xsd"
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
> <General>
>     <Window width="512" height="256"/>
>     <BoundingBox SRS="EPSG:4326" minx="-142" miny="40.5" maxx="-51.5"
> maxy="84.5"/>
>     <Title>NLWIS Map</Title>
>         <Extension>
>             <ol:maxExtent xmlns:ol="http://openlayers.org/context"
> minx="-2750000" miny="-900000" maxx="3250000" maxy="3900000"/>
>         </Extension>
>   </General>
>   <LayerList>
>         <Layer queryable="1" hidden="0">
>             <Server service="OGC:WMS" version="1.1.1" title="National
> Atlas WMS">
>                 <OnlineResource xlink:type="simple"
> xmlns:xlink="http://www.w3.org/1999/xlink"
> xlink:href="http://atlas.gc.ca/cgi-bin/atlaswms_en?"/>
>             </Server>
>             <Name>can_1m_bound</Name>
>             <Title>Boundaries (1:1 000 000)</Title>
>             <SRS>EPSG:4326</SRS>
>             <Extension>
>                 <ol:maxExtent xmlns:ol="http://openlayers.org/context"
> minx="-142" miny="40.5" maxx="-51.5" maxy="84.5"/>
>             </Extension>
>         </Layer>
>   </LayerList>
> </ViewContext>
>
> ------------------------------------------------------------------------
> --------
>
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>   

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