[MetaCRS] EPSG:3785

[Frank Warmerdam]

Norm Olsen wrote:
> 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.

Folks,

I would really appreciate it if we as MetaCRS could come to some reasonable
firm conclusion on a recommendation for how this coordinate system should
be represented.

I asked here before and there were various responses with approaches in
CS_MAP, ArcGIS, Geotoolkit and others but I don't feel like we reached any
conclusion as to a recommendation.

I have to admit I am leery of treating this coordinate system as a special
projection method.  It is just normal mercator except that we want to
use different ellipsoidal parameters in the projection calculation than
we want to use in geographic interpretation of the lat/long (which we
wish to treat as WGS84).  I'm pretty sure there are several other projections
that operate similarly in common scientific usage.

For what it's worth, I'm using these representations which
takes advantage of the my extension hack.  This is clearly useless
as an interoperable representation.

PROJCS["Popular Visualisation CRS / Mercator (deprecated)",
     GEOGCS["Popular Visualisation CRS",
         DATUM["Popular_Visualisation_Datum",
             SPHEROID["Popular Visualisation Sphere",6378137,0,
                 AUTHORITY["EPSG","7059"]],
             TOWGS84[0,0,0,0,0,0,0],
             AUTHORITY["EPSG","6055"]],
         PRIMEM["Greenwich",0,
             AUTHORITY["EPSG","8901"]],
         UNIT["degree",0.01745329251994328,
             AUTHORITY["EPSG","9122"]],
         AUTHORITY["EPSG","4055"]],
     UNIT["metre",1,
         AUTHORITY["EPSG","9001"]],
     PROJECTION["Mercator_1SP"],
     PARAMETER["central_meridian",0],
     PARAMETER["scale_factor",1],
     PARAMETER["false_easting",0],
     PARAMETER["false_northing",0],
     EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +
x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"],
     AUTHORITY["EPSG","3785"],
     AXIS["X",EAST],
     AXIS["Y",NORTH]]

PROJCS["WGS 84 / Pseudo-Mercator",
     GEOGCS["WGS 84",
         DATUM["WGS_1984",
             SPHEROID["WGS 84",6378137,298.257223563,
                 AUTHORITY["EPSG","7030"]],
             AUTHORITY["EPSG","6326"]],
         PRIMEM["Greenwich",0,
             AUTHORITY["EPSG","8901"]],
         UNIT["degree",0.01745329251994328,
             AUTHORITY["EPSG","9122"]],
         AUTHORITY["EPSG","4326"]],
     UNIT["metre",1,
         AUTHORITY["EPSG","9001"]],
     PROJECTION["Mercator_1SP"],
     PARAMETER["central_meridian",0],
     PARAMETER["scale_factor",1],
     PARAMETER["false_easting",0],
     PARAMETER["false_northing",0],
     EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 
+x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"],
     AUTHORITY["EPSG","3857"],
     AXIS["X",EAST],
     AXIS["Y",NORTH]]


-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent