Orhographic reprojection fails if given an elliptical datum in the CRS
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Key: GEOT-1554
URL: http://jira.codehaus.org/browse/GEOT-1554
Project: GeoTools
Issue Type: Bug
Components: core referencing
Affects Versions: 2.3.1
Reporter: Judd Taylor
Assignee: Martin Desruisseaux
Priority: Minor
If the CRS for an orthographic projection is given along with a datum, then an
assumption is made that you are wanting an elliptical orthographic projection,
and the projection fails.
An orthographic projection is spherical by definition, so elliptical _is_
invalid, however, all other tools out there (proj, notably), just assume
spherical based on the semi_major axis if an ellipsoid datum is given. Geotools
should work the same way.
By programatically defining an ortho CRS based on the WGS84 datum, this WKT is
produced:
PROJCS["Orthographic.WGS84.lat32.87894.lon-96.99886",
GEOGCS["WGS84",
DATUM["WGS84",
SPHEROID["WGS84", 6378137.0, 298.257223563]],
PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295],
AXIS["Geodetic longitude", EAST],
AXIS["Geodetic latitude", NORTH]],
PROJECTION["Orthographic"],
PARAMETER["central_meridian", -96.99886],
PARAMETER["latitude_of_origin", 32.87894000000001],
PARAMETER["scale_factor", 1.0],
PARAMETER["false_easting", 0.0],
PARAMETER["false_northing", 0.0],
UNIT["m", 1.0],
AXIS["Easting", EAST],
AXIS["Northing", NORTH]]
However, attempting to use this CRS fails, stating that it can't use an
elliptical datum. The work around is to manually add the semi_major and
semi_minor radius definitions:
PROJCS["Orthographic.WGS84.lat32.87894.lon-96.99886",
GEOGCS["WGS84",
DATUM["WGS84",
SPHEROID["WGS84", 6378137.0, 298.257223563]],
PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295],
AXIS["Geodetic longitude", EAST],
AXIS["Geodetic latitude", NORTH]],
PROJECTION["Orthographic"],
PARAMETER["semi_major", 6378137.0],
PARAMETER["semi_minor", 6378137.0],
PARAMETER["central_meridian", -96.99886],
PARAMETER["latitude_of_origin", 32.87894000000001],
PARAMETER["scale_factor", 1.0],
PARAMETER["false_easting", 0.0],
PARAMETER["false_northing", 0.0],
UNIT["m", 1.0],
AXIS["Easting", EAST],
AXIS["Northing", NORTH]]
But as I said before, this shouldn't be necessary, as all other software out
there just ignores any definition of the semi_minor axis when an ellipsoid is
given.
-Judd
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