[Geotools-gt2-users] Comparing CRS

[Gary Jackson <bargle@um...>]

This is the WKT for the base CRS that I get out of a GeoCover GeoTIFF file:

GEOGCS["WGS 84", 
  DATUM["WGS_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["Lon", EAST], 
  AXIS["Lat", NORTH], 
  AUTHORITY["EPSG","4326"]]

This is the WKT that I get out of a shapefile created with ArcCatalog and
edited with ArcMap:

GEOGCS["GCS_WGS_1984", 
  DATUM["D_WGS_1984", 
    SPHEROID["WGS_1984", 6378137.0, 298.257223563]], 
  PRIMEM["Greenwich", 0.0], 
  UNIT["degree", 0.017453292519943295], 
  AXIS["Lon", EAST], 
  AXIS["Lat", NORTH]]

They are (or at least should be) the same.  However, nothing I've tried
(equals(Object), equals(AbstractIdentifiedObject, boolean)) will evaluate
them that way.  Furthermore, neither are equal to the
DefaultGeographicCRS.WGS84 instance.  Is there a way to normalize these
objects so that I can compare them?  Is there another way to compare them
that will succeed?  Thank you in advance for any clues you could give me!

-- 
                                        Gary Jackson
                                        bargle@...

Re: [Geotools-gt2-users] Comparing CRS

[Martin Desruisseaux <martin.desruisseaux@no...>]

Gary Jackson a =E9crit :
> This is the WKT for the base CRS that I get out of a GeoCover GeoTIFF f=
ile:
>=20
> GEOGCS["WGS 84",=20
>   DATUM["WGS_1984",=20
>     [...snip...]
>=20
> This is the WKT that I get out of a shapefile created with ArcCatalog a=
nd
> edited with ArcMap:
>=20
> GEOGCS["GCS_WGS_1984",=20
>   DATUM["D_WGS_1984",=20
>     [...snip...]
>=20
> They are (or at least should be) the same.  However, nothing I've tried
> (equals(Object), equals(AbstractIdentifiedObject, boolean)) will evalua=
te
> them that way.  Furthermore, neither are equal to the DefaultGeographic=
CRS.WGS84 instance.


There is two issues here:

1) The comparaison must ignore metadata (e.g. the names and the=20
AUTHORITY elements) because they are not the same. Concequently we have=20
to use equals(AbstractIdentifiedObject, false); Note: you can also use=20
the convenience method CRSUtilities.equalsIgnoreMetadata(...), but this=20
method will move in a more visible place in a future version.

2) In the particular case of Datum, the name is relevant and never=20
ignored (because there is no other way to determine if two datum are=20
equals). However, Geotools contains a list of aliases and should have=20
detected that "WGS_1984" and "D_WGS_1984" are synonymous at least when=20
using the DefaultGeographicCRS.WGS84 instance with equals(..., false) or=20
equalsIgnoreMetadata(...). Did you tried this later case with Geotools=20
2.1 or above? If it still fails, then it is probably a bug and I will=20
investigate it.

	Martin.