Re: [Geotools-gt2-users] error when trying to use WKT projections without library gt-epsg-hsql-2.6.3.jar

[Jean M. <jm...@ho...>]

looking in 
details at the way I get the WKT string, I notice that sometimes 
this
 string contains the Bursa-Wolf parameters and sometimes it doesn't ;
Bursa-Wolf parameters seems related to the presence of parameter TOWGS84[..] 

to get this WKT string I write the following code :

CoordinateReferenceSystem crsSrc = ReferencingFactoryFinder.getCRSAuthorityFactory("EPSG", null).createCoordinateReferenceSystem(EPSGsrc);
and then crsSrc.toWKT() gives the WKT specification for EPSGsrc

if EPSGsrc="EPSG:2056" (Liechtenstein and Switzerland) I do get the parameter TOWGS84[..] in the WKT string
and then the library gt-epsg-hsql-2.6.3.jar is not required and the use of WKT projections is correct 
(as described in my code at the bottom of this email))

if EPSGsrc="EPSG:27572" (France) I don't get parameter TOWGS84[..] and the library gt-epsg-hsql-2.6.3.jar is required

so my question is :
how can I get a complete and an accurate WKT string from a given EPSG code ?

thanks a lot

Jean-Marie


From: jm...@ho...
To: geo...@li...
Date: Wed, 12 May 2010 11:36:28 +0200
Subject: Re: [Geotools-gt2-users] error when trying to use WKT projections without library gt-epsg-hsql-2.6.3.jar








thanks Andrea for your answer
i could checked in my example what you said ; the error is too big regarding the latitude (around 345 meters !)

well does it mean that I can't take into account Bursa-Wolf parameters without using gt-epsg-hsql-2.6.3.jar ?
or is there a way to make this library lighter ?

cheers

Jean-Marie


> Date: Wed, 12 May 2010 11:07:33 +0200
> From: aa...@op...
> To: jm...@ho...
> CC: geo...@li...
> Subject: Re: [Geotools-gt2-users] error when trying to use WKT projections  without library gt-epsg-hsql-2.6.3.jar
> 
> Jean Marie ha scritto:
> > Hello
> > 
> > I begin to use GeoTools to create projections described in WKF format in 
> > order to proceed tranformations ;
> > but to achieve this, it seems that I can't avoid the library 
> > gt-epsg-hsql-2.6.3.jar
> > while I think that gt-referencing-2.6.3.jar was enough ;
> > 
> > as an example I give you the code below which works fine if I add 
> > gt-epsg-hsql-2.6.3.jar
> > 
> > // transformation WGS 84 --> French Lambert zone II
> > 
> > double Longitude=1.515; double Latitude=46.675 ;
> > String wktsrc="GEOGCS[\"WGS 84\", DATUM[\"World Geodetic System 
> > 1984\",....";
> > String wktdst="PROJCS[\"NTF (Paris) / Lambert zone II\",GEOGCS[\"NTF 
> > (Paris)\",.....";
> > 
> > CoordinateReferenceSystem crsSrc = CRS.parseWKT(wktsrc);
> > CoordinateReferenceSystem crsDest = CRS.parseWKT(wktdst);
> > CoordinateOperation op = coFactory.createOperation(crsSrc, crsDest);
> 
> Use CRS.findMathTransform(crsSrc, crsDest, true)
> that should work fine.
> 
> Of course without Bursa-Wolf parameters in the definitions you'll get
> big transfromation errors (40-80 meters usually, the actual value
> varies a lot depending on the actual data, don't know what will be
> in your case)
> 
> Cheers
> Andrea
> 
> -- 
> Andrea Aime
> OpenGeo - http://opengeo.org
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