[MetaCRS] EPSG:3785

[Norm Olsen]

Hello All . . .

As of revision 1619 (15 Sept 2009) CS_MAP now supports the Popular "Visualisation Pseudo Mercator" projection.  A coordinate reference system definition named "WGS84.PseudoMercator" is now included in the dictionaries.  It is referenced to the WGS84 datum, as its name implies.  All other parameters are equivalent to that specified by EPSG::3857.

Norm

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Mikael Rittri
Sent: Wednesday, October 07, 2009 7:45 AM
To: Christopher Schmidt; bartvde at osgis.nl
Cc: metacrs at lists.osgeo.org
Subject: RE: [MetaCRS] EPSG:3785


Chris wrote:

> It's now 3857 instead of 3785. So far as I can tell, nothing about 
> how it's represented or handled in WKT or in any other way changed.

Well, there are some differences.
 
The old EPSG:3785 had a geodetic datum whose reference ellipsoid
was a perfect sphere, and the projection method was "Mercator
(Spherical)",
coord. op. method code 1026, which apparantly is meant to be applied
only
to spheres.
  However, EPSG suggested the datum shift +towgs84=0,0,0 to transform
between the 
sphere and the WGS84 ellipsoid, and this would change the latitudes,
which is not 
what Google does. 

The new EPSG:3857 has WGS84 as geodetic datum, and the projection method
is
now "Popular Visualisation Pseudo Mercator", coord. op. method code
1024,
which is permitted to use on an non-spherical ellipsoid.  
The formulas are the same as for "Mercator (Spherical)", but the 
the radius of the internally used sphere is by definition the same 
as the equatorial radius of the ellipsoid. 

This should give some differences in WKT.  You would see a 
true ellipsoid instead of a sphere in the datum definition,
for example.  But I am not sure if any GIS companies support the 
"Popular Visualisation Pseudo Mercator" as a projection method in WKT.

-- 
Mikael Rittri
Carmenta AB
Sweden
www.carmenta.com 

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org
[mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Christopher
Schmidt
Sent: den 7 oktober 2009 15:22
To: bartvde at osgis.nl
Cc: metacrs at lists.osgeo.org
Subject: Re: [MetaCRS] EPSG:3785

On Wed, Oct 07, 2009 at 03:17:31PM +0200, bartvde at osgis.nl wrote:
> Hi list,
> 
> does anyone know what happened to EPSG:3785 (the Google Maps
projection)?
> 
> It used to be in the EPSG database, but now it's gone, and the only 
> thing I can find is in the EPSG database SQL scripts:

Right. It's now 3857 instead of 3785. So far as I can tell, nothing
about how it's represented or handled in WKT or in any other way
changed. (Though perhaps they decided to remove the snarky comment in
the description.)

-- Chris

> INSERT INTO epsg_deprecation VALUES ( 1067, '2009-02-10', 2008.114, 
> 'Coordinate Reference System', 3785, 3857, 'OGP revised its approach 
> to description of Popular Visualisation CRS.' );
> 
> TIA.
> 
> Best regards,
> Bart
> 
> 
> 
> _______________________________________________
> MetaCRS mailing list
> MetaCRS at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/metacrs

--
Christopher Schmidt
MetaCarta
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