[OpenLayers-Users] epsg:3857 and google 900913

Thu Jan 17 23:55:29 PST 2013

Arnd, Sergant_york

Thats actually quite scary on one hand, but thanks a lot for clarifying it
for me!

Casper

On Thu, Jan 17, 2013 at 7:46 PM, Arnd Wippermann <arnd.wippermann at web.de>wrote:

> **
> Hi Caspar,
>
> "If the layer projection equals the mapprojection, the layer projection
> is returned"
>
> In the case of map projection = EPSG:900913 and a WMS projection =
> EPSG:3857 the WMS GetMap Request will use EPSG:3857.
> Because EPSG:900913 equals EPSG:3857. Declared in Projection.js.
>
> For other projections and aliases OpenLayers cann't decide equality and
> the map projection will be used.
>
> If you include the proj4js-library to your application, then OpenLayers
> tests for equality by text comparision of the proj-strings and that may
> lead to other results as above, if the proj-strings not ===.
> But it would also provide a possibility to add other projections and
> aliases to ones applications.
>
> Arnd
>  ------------------------------
> *Von:* Casper Span [mailto:info at spatially-oriented.com]
> *Gesendet:* Donnerstag, 17. Januar 2013 08:51
> *An:* arnd.wippermann at web.de
>
> *Cc:* openlayers-users at lists.osgeo.org
> *Betreff:* Re: [OpenLayers-Users] epsg:3857 and google 900913
>
>   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
>
>

-- 

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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