[OpenLayers-Users] SphericalMercator and SRS aliases epsg:900913, epsg:3857, epsg:3785, epsg:102113

[christopher.schmidt at nokia.com]

On Jul 19, 2010, at 8:51 AM, ext Anne Blankert wrote:

> 
>  Hello Bart,
> 
> My 2 cents:
> In my opinion it is quite difficult for users to discover:
> - OpenStreetMap, Google, Bing, Yahoo etc. use a projection called 
> 'SphericalMercator'
> - 'SphericalMercator' in OpenLayers uses code 'epsg:900913'

I think this is reasonably well documented in 
 
  http://docs.openlayers.org/library/spherical_mercator.html 

and if you search for:

 http://docs.openlayers.org/search.html?q=google+projection

You get that as one of the results. (Not as highly ranked as I would
like, I'll admit, but it is there.)

> - there exist multiple aliases for 'epsg:900913' and some services 
> prefer alias epsg:3857 or epsg:102113 over epsg:900913
> - how to override the default openlayers sphericalmercator epsg code 
> with an other epsg code

This being supported is something I'd question ;) Until very recently,
I'm pretty sure it was not at all possible to do this, so it's not really
a surprised that it isn't well documented, in my opinion.

> - discover that the override produces side effects in measurement and 
> mouseposition (and other functions, such as click-events...?)
> - how to solve the side effects, by adding code:
> OpenLayers.Projection.addTransform("EPSG:4326", "EPSG:3857", 
> OpenLayers.Layer.SphericalMercator.projectForward);
> OpenLayers.Projection.addTransform("EPSG:3857", "EPSG:4326", 
> OpenLayers.Layer.SphericalMercator.projectInverse);
> 
> But instead of solving this in the library, this can also be part of the 
> documentation. Maybe that documentation already exists and I've 
> overlooked it?

No documentation like this exists at this time that I'm aware of.

-- Chris

> 
> Cheers,
> 
> Anne
> 
> On 7/19/2010 1:15 PM, Bart van den Eijnden (OSGIS) wrote:
>> Hi Anne,
>> 
>> check the example (first couple of lines in comments):
>> 
>> http://trac.openlayers.org/browser/trunk/openlayers/examples/web-mercator.js?rev=10384
>> 
>> So that's up to the application to provide (at least for now). But I can
>> also see that's not really easy for end-users.
>> 
>> What do other people think about providing the EPSG aliases by default in
>> the OL library?
> 
> 
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Regards,
-- 
Christopher Schmidt
Nokia