Re: [Geotools-gt2-users] system coordinates convertion

[Michael B. <mic...@gm...>]

Hello Danilo,

It seems to be related to the definition of the Google projection. The
snippet below uses EPSG:4326 instead and the results are fine.
However, I've no idea exactly what the problem is. Perhaps Andrea
(referencing module maintainer) can comment.

    Coordinate[] coordinates = new Coordinate[]{
        new Coordinate(-49.00, -16.683),
        new Coordinate(-49.300, -16.675)};

    Geometry geom = new GeometryFactory().createLineString(coordinates);
    CoordinateReferenceSystem geo = CRS.decode("EPSG:4326", true);
    CoordinateReferenceSystem utm = CRS.decode("EPSG:31982", true);

    MathTransform trForward = CRS.findMathTransform(geo, utm);
    Geometry geomForward = JTS.transform(geom, trForward);

    MathTransform trBack = CRS.findMathTransform(utm, geo);
    Geometry geomBack = JTS.transform(geomForward, trBack);

    System.out.println(geom);
    System.out.println(geomForward);
    System.out.println(geomBack);

Michael

On 18 November 2011 00:21, Danilo Marques de Rezende
<dan...@gm...> wrote:
> Hello,
> I am trying to make some coordinates converstion from mercator to utm, and
> it seens
> that I make something wrong.
> To make sure the convertion is correct, I tryed to convert back to mercator.
> Here is the code that I used:
> ...
> //tryed using coordinates lat,lon as x,y; and lat,lon as y,x
> Coordinate[] coordinates = new Coordinate[] {
>                         new Coordinate(-49.00, -16.683),
>                         new Coordinate(-49.300, -16.675)};
> Geometry g3 = new GeometryFactory().createLineString(coordinates);
> sourceCRS = CRS.decode("EPSG:3785"); // Mercator/google maps code
> targetCRS = CRS.decode("EPSG:31982");  //  UTM 22s code
> from http://www.epsg-registry.org/
> MathTransform tx = CRS.findMathTransform(CRSFrom, CRSTo, true);
> Geometry transformed = JTS.transform(geom, transform)
> The result is this:
> first convertion to utm coodinates:
> [(6120584.969417981, 1.0000023079023875E7, NaN),
> (6120584.546247176, 1.0000023090352934E7, NaN)]
> convertion back to Mercator:
> [(-8997.836054457479, -17.077226626756676, NaN),
>  (-8998.130646014215, -17.069201880507137, NaN)]
> Am I doing something wrong?
> Thanks,
> --
> Danilo Marques
>
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