Re: [Geotools-gt2-users] Coordinates transformation from CRS.parseWKT

[Christian G. <chr...@gm...>]

Thanks for you answer Jody.

The PROJ.4 definition is :
+proj=lcc +lat_1=46.8 +lat_0=46.8 +lon_0=0 +k_0=0.99987742 +x_0=600000
+y_0=2200000 +a=6378249.2 +b=6356515 +towgs84=-168,-60,320,0,0,0,0
+pm=paris +units=m +no_defs

So I'm using the same TOWGS84 parameter : TOWGS84[-168,-60,320,0,0,0,0]
http://spatialreference.org/ref/epsg/27572/ogcwkt/

So I have no idea what may be wrong.

Thanks again,

Christian

On Mon, Nov 18, 2013 at 7:01 PM, Jody Garnett <jod...@gm...> wrote:
> Well you have a small clue, that "lenient" is used when the two coordinate
> systems use a different model for the shape of the earth, so no correct
> transformation exists between the two systems. Indeed we can see that, in
> the definition.
>
> So you are not doing anything wrong, question is what do you want to do? You
> are going to have to make an assumption on how to do the DATM shift, but
> what assumption do you want to make?  Sounds like you would like to make the
> same assumption as PROJ....
>
> Check what PROJ is doing and copy their "+towgs84" parameters when
> constructing your WKT by hand.
>
> Jody
>
> Jody Garnett
>
>
> On Tue, Nov 19, 2013 at 5:41 AM, Christian Gendreau
> <chr...@gm...> wrote:
>>
>> Hi,
>>
>> I'm trying to convert/transform some coordinates from one CRS to
>> another using JTS.transform(...)
>> There is a difference in what GeoTools 10 returns and what PostGIS and
>> QGIS return.
>> I'm aware that the parameters used by GeoTools are from the EPSG
>> database and are not managed by GeoTools but I'm having an issue when
>> I provide the exact WTK.
>>
>> Input is in EPSG:27572 (Lambert zone II)
>> -------
>> CoordinateReferenceSystem sourceCrs = CRS.decode("EPSG:27572");
>> CoordinateReferenceSystem targetCrs = DefaultGeographicCRS.WGS84;
>>
>> Coordinate coord = new Coordinate(605937.033, 2426318.714);
>> Point sourcePoint = geometryFactory.createPoint(coord);
>> MathTransform transform = CRS.findMathTransform(sourceCrs, targetCrs);
>> Geometry targetGeometry = JTS.transform( sourcePoint, transform);
>> -------
>>
>> This will not work except if I use the 'lenient' flag and then I will get:
>> POINT (2.4180555600606395 48.832161511178725)
>> This is 400 meters offset but there is no TOWGS84 parameters provided
>> so I'm don't know what accuracy to expect.
>>
>> So I tried with PostGIS 2.0.1 and I got : POINT(2.41733554398175
>> 48.8352090484985)
>> This is correct.
>>
>> Then, I tried to use the PostGIS WTK definition in GeoTools.
>>
>> crs = CRS.parseWKT("PROJCS[\"NTF (Paris) / Lambert zone
>> II\",GEOGCS[\"NTF
>>
>> (Paris)\",DATUM[\"Nouvelle_Triangulation_Francaise_Paris\",SPHEROID[\"Clarke
>> 1880
>> (IGN)\",6378249.2,293.4660212936265,AUTHORITY[\"EPSG\",\"7011\"]],TOWGS84[-168,-60,320,0,0,0,0],AUTHORITY[\"EPSG\",\"6807\"]],PRIMEM[\"Paris\",2.33722917,AUTHORITY[\"EPSG\",\"8903\"]],UNIT[\"grad\",0.01570796326794897,AUTHORITY[\"EPSG\",\"9105\"]],AUTHORITY[\"EPSG\",\"4807\"]],UNIT[\"metre\",1,AUTHORITY[\"EPSG\",\"9001\"]],PROJECTION[\"Lambert_Conformal_Conic_1SP\"],PARAMETER[\"latitude_of_origin\",52],PARAMETER[\"central_meridian\",0],PARAMETER[\"scale_factor\",0.99987742],PARAMETER[\"false_easting\",600000],PARAMETER[\"false_northing\",2200000],AUTHORITY[\"EPSG\",\"27572\"],AXIS[\"X\",EAST],AXIS[\"Y\",NORTH]]");
>>
>> and I got: POINT (2.183603198566145 48.8352075151015)
>> which is 17 km offset.
>>
>> Does anyone know what I'm doing wrong?
>>
>> Thanks,
>>
>> Christian Gendreau
>>
>>
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