[Geoserver-users] Wrong Google Projection 900913?

GeoServer GeoServer User
1

I am using Geoserver 1.7.0

I tried to add a FeatureType that is based an the "900913"-CRS.
Geoserver uses the following SRS for the "Google Projection":

PROJCS["WGS84 / Google Mercator",
  GEOGCS["WGS 84",
    DATUM["World Geodetic System 1984",
      SPHEROID["WGS 84", 6378137.0, 298.257223563,
AUTHORITY["EPSG","7030"]],
      AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
    UNIT["degree", 0.017453292519943295],
    AXIS["Longitude", EAST],
    AXIS["Latitude", NORTH],
    AUTHORITY["EPSG","4326"]],
  PROJECTION["Mercator_1SP"],
  PARAMETER["semi_minor", 6378137.0],
  PARAMETER["latitude_of_origin", 0.0],
  PARAMETER["central_meridian", 0.0],
  PARAMETER["scale_factor", 1.0],
  PARAMETER["false_easting", 0.0],
  PARAMETER["false_northing", 0.0],
  UNIT["m", 1.0],
  AXIS["x", EAST],
  AXIS["y", NORTH],
  AUTHORITY["EPSG","900913"]]

As far as I know is the datum of the "Google Projection" a sphere and not
the WGS84 ellipsoid.

http://spatialreference.org/ref/user/google-projection/
http://spatialreference.org/ref/user/google-projection/

By the way, the EPSG published an update on their
http://www.epsg.org/Geodetic.html crs list including a new "web mapping
crs" (EPSG:3785):

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_1SP"],
    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"]]

http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx
http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx

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2

Geoflo ha scritto:

I am using Geoserver 1.7.0

I tried to add a FeatureType that is based an the "900913"-CRS.

So you have data that has been generated directly in the Google
projection? Weird.

Geoserver uses the following SRS for the "Google Projection":

PROJCS["WGS84 / Google Mercator", GEOGCS["WGS 84", DATUM["World Geodetic System 1984", SPHEROID["WGS 84", 6378137.0, 298.257223563,
AUTHORITY["EPSG","7030"]], AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], UNIT["degree", 0.017453292519943295], AXIS["Longitude", EAST], AXIS["Latitude", NORTH], AUTHORITY["EPSG","4326"]], PROJECTION["Mercator_1SP"], PARAMETER["semi_minor", 6378137.0], PARAMETER["latitude_of_origin", 0.0], PARAMETER["central_meridian", 0.0], PARAMETER["scale_factor", 1.0], PARAMETER["false_easting", 0.0], PARAMETER["false_northing", 0.0], UNIT["m", 1.0], AXIS["x", EAST], AXIS["y", NORTH], AUTHORITY["EPSG","900913"]]

As far as I know is the datum of the "Google Projection" a sphere and not
the WGS84 ellipsoid.

http://spatialreference.org/ref/user/google-projection/
http://spatialreference.org/ref/user/google-projection/

Yeah, sort of. The thing is, the datum is a sphere but the reprojection
library does not have to compensate for the difference between the
ellipsoidal and spherical datums when reprojecting from, say, 4326
to 900913. In our definition
PARAMETER["semi_minor", 6378137.0]
takes care exactly of that, whilst for the Proj library it's the
+nadgrids=@null parameters that does the same work:
http://spatialreference.org/ref/user/google-projection/proj4/

By the way, the EPSG published an update on their http://www.epsg.org/Geodetic.html crs list including a new "web mapping
crs" (EPSG:3785):

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_1SP"],
    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"]]

http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx
http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx

Yeah, I know, unfortunately no one has had the time to upgrade our
EPSG database provider.

Cheers
Andrea

--
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.