Loïc MAZE a écrit :
Everything works but the result isn't accurate. For example, I have a
point at longitude 5.08° east and at latitude 47.31° north (in WGS84).
The result of the transformation is a point with the following coords :
X = 807332 meters and Y = 2260657 meters.
The correct point will have those coords :
X = 807389 meters and Y = 2260315 meters.
Do you know where the correct point come from? Which parameters were used for
computing it?
The following line added to yours source code:
System.out.println(targetCRS);
produces the following output:
PROJCS["NTF (Paris) / Lambert zone II",
GEOGCS["NTF (Paris)",
DATUM["Nouvelle Triangulation Francaise (Paris)",
SPHEROID["Clarke 1880 (IGN)", 6378249.2, 293.4660212936269,
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"]]
Note: This is "Well Know Text" format (WKT), which is defined by OGC (not a custom Geotools format).
I understand that it seems unfriendly at a first look. But it is really worth to become familiar
with it, since it is of great help for understanding what is going on and debugging.
The interesting part is that the SPHEROID[...] element is something else than "WGS 84" ("Clarke 1880
(IGN)" in the above case), but there is no TOWGS84[...] element defined. Concequently, Geotools
don't know how to apply a datum shift from "WGS 84" to "Clarke 1880 (IGN)". This is why you got a
"Bursa Wolf parameters required" exception when trying to get the transformation without
Hints.LENIENT_DATUM_SHIFT set to Boolean.TRUE. The LENIENT_DATUM_SHIFT hint shutdown the warning,
but hey! this warning was telling you that the transformation may be innacurate because some
information are missing, so you are supposed to know what you are doing if you shutdown the warning
and process anyway ;)
The consequence of missing TOWGS84[...] element can be seen if you add the
following line of code:
System.out.println(transform);
It produces the following output:
CONCAT_MT[PARAM_MT["Affine",
PARAMETER["num_row", 3],
PARAMETER["num_col", 3],
PARAMETER["elt_0_0", 0.0],
PARAMETER["elt_0_1", 1.0],
PARAMETER["elt_1_0", 1.0],
PARAMETER["elt_1_1", 0.0]],
PARAM_MT["Molodenski",
PARAMETER["dim", 2],
PARAMETER["dx", 0.0],
PARAMETER["dy", 0.0],
PARAMETER["dz", 0.0],
PARAMETER["src_semi_major", 6378137.0],
PARAMETER["src_semi_minor", 6356752.314245179],
PARAMETER["tgt_semi_major", 6378249.2],
PARAMETER["tgt_semi_minor", 6356515.0]],
PARAM_MT["Affine",
PARAMETER["num_row", 3],
PARAMETER["num_col", 3],
PARAMETER["elt_0_2", -2.33722917]],
PARAM_MT["Lambert_Conformal_Conic_1SP",
PARAMETER["semi_major", 6378249.2],
PARAMETER["semi_minor", 6356515.0],
PARAMETER["central_meridian", 0.0],
PARAMETER["latitude_of_origin", 46.8],
PARAMETER["scale_factor", 0.99987742],
PARAMETER["false_easting", 600000.0],
PARAMETER["false_northing", 2200000.0]]]
The interresting point is that the "dx", "dy" and "dz" parameter values inside the "Molodenski"
block are set to 0. This is a concequence of missing "TOWGS84[...]" info.
Now, the question is whatever TOWGS84 info should exists or not. Make sure that *one* of
epsg-access, epsg-hsql or epsg-postgresql is in yours classpath, and make sure that epsg-wkt is
*not* in yours classpath (because epsg-wkt to not contains any TOWGS84 info).
If Geotools still unable to find TOWGS84 info using epsg-access with latest EPSG database (I tried
with EPSG version 6.9), there is two choice:
- Either the info exists but Geotools was unable to find it, in which case
this is a Geotools bug.
- Or either the info do not exists or should not exists in the EPSG database.
I suggest to search manually in the EPSG database. I did a quick search (more specifically, I
searched for "27572" in both the "Source" and "Target" columns of "Coordinate_Operation" table) and
found nothing. But it may be worth to try harder (for example search for any coordinate operation
involving the "Clarke 1880 (IGN)" ellipsoid). Try to upgrate to latest EPSG database if a more
recent version is available (http://www.epsg.org).
If you find an information in the EPSG database that Geotools should have been able to find by
itself, please let me known.
Otherwise, you may try to search outside EPSG (maybe google) for "Bursa Wolf Parameters",
"Molodenski", "Position Vector 7-param. transformation", "Coordinate Frame rotation" etc. involving
"Nouvelle Triangulation Francaise (Paris)" or "Clarke 1880 (IGN)", and let me know what you find.
Martin.
-------------------------------------------------------
Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
http://sel.as-us.falkag.net/sel?cmd=lnk&kid0709&bid&3057&dat1642
_______________________________________________
Geotools-gt2-users mailing list
Geotools-gt2-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
