[OpenLayers-Users] epsg:3857 and google 900913

[Casper Span]

Arnd,

I'm talking about lines 247-251 from wms.js (
https://github.com/openlayers/openlayers/blob/master/lib/OpenLayers/Layer/WMS.js
):

var mapProjection = this.map.getProjectionObject();
var projectionCode = this.projection &&
this.projection.equals(mapProjection) ? this.projection.getCode() :
mapProjection.getCode();
var value = (projectionCode == "none") ? null : projectionCode;

If the layer projection equals the mapprojection, the layer projection is
returned. If not, the mapprojection is returned.

Correct me if I'm wrong, but that would say it always returns the map
projection code, no matter what I fill in on the projection code or when I
fill it.

I came across this piece of code after building a WMS server with SharpMap.
I only built in support for EPSG:3857 but the default OSM layer is in
EPSG:900913. My WMS server kept coming with error "SRS 900913 not supported"
Please note that in my case the WMS layer is NOT my base layer. If it was,
it WOULD listen to the projection of the layer (as the Map.Projection asks
it's baselayer for the projection)

Casper


On Wed, Jan 16, 2013 at 11:13 PM, Arnd Wippermann <arnd.wippermann at web.de>wrote:

> **
> Hi Caspar,
>
> "In other words, it will only use the map projection in it's WMS request
> URL's"
>
> That's not right as you have found out by yourself. If the map projection
> is equal the wms projection, then the WMS GetMap Request use the wms
> projection.
>
> Some servers provide only requests for EPSG:3857 (an alias for
> EPSG:900913) and if you use for your map EPSG:900913, then you can add
> these servers and set the projection to EPSG:3857 and it works.
>
> But it seems, that that only works for EPSG:900913 and EPSG:4326 and their
> aliases, because OpenLayers has aliases defined in OpenLayers Projection.js.
>
> If you have maps with other projections and a server support only an alias
> of the projection, then the above will perhaps not work.
>
> Then the only way is to overwrite the getFullRequestString-method of
> OpenLayers.Layer.WMS.
>
> Example
> http://gis.ibbeck.de/ginfo/apps/OLExamples/OL212/wms_options_projection.asp
>
> Arnd
>
>
>  ------------------------------
> *Von:* openlayers-users-bounces at lists.osgeo.org [mailto:
> openlayers-users-bounces at lists.osgeo.org] *Im Auftrag von *Casper Span
> *Gesendet:* Mittwoch, 16. Januar 2013 12:53
> *An:* Sergeant_york
> *Cc:* openlayers-users at lists.osgeo.org
> *Betreff:* Re: [OpenLayers-Users] epsg:3857 and google 900913
>
>     Hi,
>
> If you look at the source of WMS (lib\OpenLayers\Layer\WMS.js), take a
> look at getFullRequestString.
> In it, the baselayer's projection will always override the given
> projection. In fact, the layers projection itself will be ignored:
> - It takes the Map Projection (=Baselayer projection)
> - then, if the WMS layer projection equals the map projection, it uses the
> layer projection
> - otherwise, it uses the map projection
>
> In other words, it will only use the map projection in it's WMS request
> URL's
>
> So yeah... everything MUST be the same projection for WMS layers or it
> cannot be placed on top of eachother.
>  For me, this meant reprojecting my own data so I can serve it with WMS
> onto OSM.
>
> You can check these actual outgoing URL's with Firebug and such.
>
> regards,
> Casper Span
>
> On Wed, Jan 16, 2013 at 12:31 PM, Sergeant_york <electronicpanda at gmail.com
> > wrote:
>
>> Hello there,
>>
>> Thank you for the answer. That gave me a good idea. Unfortunately it
>> doesn't
>> work when initializing layer.
>>
>> On the other hand creating a layer (for example aLayer object) then
>> changing
>> projection works!
>>
>> Workin way is:
>> layer aLayer=new OpenLayers.Layer.WMS ......
>> aLayer.projection= new OpenLayers.Projection("EPSG:3857")
>>
>>
>>
>> --
>> View this message in context:
>> http://osgeo-org.1560.n6.nabble.com/epsg-3857-and-google-900913-tp5027619p5027809.html
>>  Sent from the OpenLayers Users mailing list archive at Nabble.com.
>> _______________________________________________
>> Users mailing list
>> Users at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/openlayers-users
>>
>
>
>
> --
>
> Casper Span
> T: @Span_Droid <https://twitter.com/#%21/Span_Droid>
> W: http://www.spatially-oriented.com
> M: info at spatially-oriented.com
>
>


-- 

Casper Span
T: @Span_Droid <https://twitter.com/#%21/Span_Droid>
W: http://www.spatially-oriented.com
M: info at spatially-oriented.com
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