Re: [Geotools-gt2-users] France Lambert 2 to WGS84 - which WKT ? (newbie)

[Martin D. <mar...@no...>]

Peter Zankl a =E9crit :
> I need to transform some given data from "Lambert 2 =E9tendu" to WGS84.
> [...snip...] Further reading: there is the EPSG database describing coo=
rdinate=20
> systems containing an entry
> INSERT INTO epsg_alias VALUES ( [...snip...], 'NTF (Paris) / Lambert zo=
ne II etendu');
> which is the closest match I can find.
>=20
> 2 questions:
> a) can anyone confirm that relating "Lambert 2 =E9tendu" to the EPSG en=
try=20
> does make sense ?
> b) where do I find the WKT string? Do I really have to install the whol=
e=20
> EPSG thing (including MS Access) to extract this single line of text ?

WKT and EPSG are two unrelated things. In order to get yours Coordinate=20
Reference System (CRS) objects, you need to describe the CRS as a "Well=20
Known Text" (WKT), or you need its EPSG code. But you don't need both.

WKT is flexible and do not requires any database at all. EPSG codes put=20
more constraints (you need an EPSG database, and you can't create a CRS=20
which is not defined in this database), but is easier to use if you know=20
the CRS code. In some cases, it allows more accurate transformations=20
than WKT.

The EPSG database is available in various forms. You can download it in=20
MS-Access format from http://www.epsg.org (MS-Access is the primary=20
distribution format for this database). You can also install it on a=20
PostgreSQL database, etc.

Geotools provides different EPSG plugins, each of them for a different=20
connection mechanism to an EPSG database. The "epsg-access" plugin=20
search for an MS-Access database registered under the "EPSG" name in the=20
"ODBC Sources" folder in the control panel. If you have a MS-Access=20
software on yours machine, I recommand this approach since it allows you=20
to browse the EPSG database in order to find the EPSG code for yours CRS.

An other Geotools plugin is "epsg-hsql", which is bundled with a copy of=20
the EPSG 6.7 database. Using the "epsg-hsql" plugin, you don't need to=20
download the EPSG database. Just put the "epsg-hsql.jar" file in yours=20
classpath, and everything should work. But you need to download the HSQL=20
database engine first...

For searching an EPSG code for a CRS, "Alias" is not the right table to=20
look into. You need to search in the "Coordinate Reference System"=20
table. For example the code 27572 is for "NTF (Paris) / Lambert zone=20
II". But there is a lot of "NTF (Paris)" CRS. Maybe you should look in=20
the EPSG database by yours self in order to be sure to pick the one you=20
want.

You can tests yours EPSG code with the following line from the command=20
line (assuming that the Geotools JAR are in yours classpath, including=20
at least one of the EPSG plugins):

java org.geotools.referencing.factory.epsg.DefaultFactory 27572

You should get the WKT for the EPSG:27572 CRS, which is:

PROJCS["NTF (Paris) / Lambert zone II",
   GEOGCS["NTF (Paris)",
     DATUM["Nouvelle Triangulation Francaise (Paris)",
       SPHEROID["Clarke 1880 (IGN)", 6378249.2, 293.4660212936269,=20
AUTHORITY["EPSG","7011"]],
       AUTHORITY["EPSG","6807"]],
     PRIMEM["Paris", 2.5969213, AUTHORITY["EPSG","8903"]],
     UNIT["grade", 0.015707963267948967],
     AXIS["Geodetic latitude", NORTH],
     AXIS["Geodetic longitude", EAST],
     AUTHORITY["EPSG","4807"]],
   PROJECTION["Lambert Conic Conformal (1SP)", AUTHORITY["EPSG","9801"]],
   PARAMETER["central_meridian", 0.0],
   PARAMETER["latitude_of_origin", 52.0],
   PARAMETER["scale_factor", 0.99987742],
   PARAMETER["false_easting", 600000.0],
   PARAMETER["false_northing", 2200000.0],
   UNIT["m", 1.0],
   AXIS["Easting", EAST],
   AXIS["Northing", NORTH],
   AUTHORITY["EPSG","27572"]]

But you don't really need this WKT. In yours code, just write:

    CRSAuthorityFactory f =3D FactoryFinder.getCRSAuthorityFactory("EPSG"=
);
    CoordinateReferenceSystem crs =3D=20
f.createCoordinateReferenceSystem("27572");

and you got yours CRS.

	Martin.