I just received an update from the EPSG mailing list:
New to Version 6.15 are (among other things): Added spherical Mercator coordinate operation method and associated CRS as seen in popular web mapping and visualisation applications.
It looks like they FINALLY added the spherical Mercator / Web Mercator projection used in Virtual Earth and Google Maps.
This is a big surprise. EPSG’s earlier statement whether to include it was this:
"We have reviewed the coordinate reference system used by Microsoft, Google, etc. and believe that it is technically flawed. We will not devalue the EPSG dataset by including such inappropriate geodesy and cartography.”
Guess they changed their mind, or did they just devalue their dataset? Then again, judging from the remarks EPSG put in there, their arrogance still shines through. There´s absolute nothing wrong with using a sphere instead of a flattened sphere. Sure it's not as accurate as for instance WGS84, but then again WGS84 is not accurate either - no ellipsoid is. But we know the exact differences between the two, and as always you will need to take these things into account so I don´t see the real issue. Viisually the distortion is far less than what you would notice, and when doing area, distance and bearing calculations you would first of all never use the mercator units without taking the projection distortion into account, and if you do your calculationg in long/lat it's more or less just as easy to use WGS84 as a base for your calculations (since no datum transform is really needed).
Anyway, finally we get an official code for "Web Mercator": EPSG:3785
Here are the details of the entry:
Full WKT with authorities (untested!):
PROJCS["Popular Visualisation CRS / Mercator", 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", 0.0174532925199433, AUTHORITY["EPSG", "9102"]], AXIS["E", EAST], AXIS["N", NORTH], AUTHORITY["EPSG",4055]], PROJECTION["Mercator"], PARAMETER["False_Easting", 0], PARAMETER["False_Northing", 0], PARAMETER["Central_Meridian", 0], PARAMETER["Latitude_of_origin", 0], UNIT["metre", 1, AUTHORITY["EPSG", "9001"]], AXIS["East", EAST], AXIS["North", NORTH], AUTHORITY["EPSG",3785]]
Projected CRS
COORD_REF_SYS_CODE: 3785
COORD_REF_SYS_NAME: Popular Visualisation CRS / Mercator
AREA_OF_USE_CODE: 3544
COORD_REF_SYS_KIND: projected
COORD_SYS_CODE: 4499
DATUM_CODE:
SOURCE_GEOGCRS_CODE: 4055 (see below)
PROJECTION_CONV_CODE: 19847
CMPD_HORIZCRS_CODE:
CMPD_VERTCRS_CODE:
CRS_SCOPE: Certain Web mapping and visualisation applications.
REMARKS: Uses spherical development. Relative to an ellipsoidal development errors of up to 800 metres in position and 0.7% in scale may arise. Some applications call this WGS 84. It is not a recognised geodetic system: see WGS 84 / World Mercator (CRS code 3395)
INFORMATION_SOURCE: Microsoft.
DATA_SOURCE: OGP
REVISION_DATE: 3/14/2008
CHANGE_ID:
SHOW_CRS: TRUE
DEPRECATED: FALSE
Geographic CRS:
COORD_REF_SYS_CODE: 4055
COORD_REF_SYS_NAME: Popular Visualisation CRS
AREA_OF_USE_CODE: 31262
COORD_REF_SYS_KIND: geographic 2D
COORD_SYS_CODE: 6422
DATUM_CODE: 6055 (see below)
SOURCE_GEOGCRS_CODE:
PROJECTION_CONV_CODE:
CMPD_HORIZCRS_CODE:
CMPD_VERTCRS_CODE:
CRS_SCOPE: Certain Web mapping and visualisation applications.
REMARKS: Some applications erroneously call this WGS 84. It uses a sphere with a radius having the same value as the semi-major axis of the WGS 84 ellipsoid. There is no geodetic recognition of this system.
INFORMATION_SOURCE: Microsoft.
DATA_SOURCE: OGP
REVISION_DATE: 3/13/2008
CHANGE_ID:
SHOW_CRS: TRUE
DATUM_CODE: FALSE
Datum:
Code: 6055
Datum Name: Popular Visualisation
Datum Type: geodetic
Origin Description: Not specified in the classical sense of defining a geodetic datum.
Datum Epoch:
Ellipsoid Code: 7059 (see below)
Prime Meridian Code: 8901
Area Code: 1262
Datum Scope : Used by certain popular Web mapping and visualisation applications.
Remarks: Not recognised by geodetic authorities.
Information Source: Microsoft.
Data Source: OGP
Revision Date: 13-Mar-08
Change ID:
Deprecated: No
Ellipsoid:
Code: 7059
Ellipsoid Name: Popular Visualisation Sphere
Semi-major axis (a): 6378137
Axes units code: 9001
Inverse flattening (1/f):
Semi-minor axis (b): 6378137
Ellipsoid?: No
Remarks: Sphere with radius equal to the semi-major axis of the GRS80 and WGS 84 ellipsoids. Used only for Web approximate mapping and visualisation. Not recognised by geodetic authorities.
Information Source: Microsoft.
Data Source: OGP
Revision Date: 14-Mar-08
Change ID:
Deprecated?: No