On Mon, Aug 10, 2015 at 10:18 AM, Davide <d...@vide.bz> wrote:
> Hi,
>
> I want to convert points from "Gauss-Boaga Roma40" to "WGS84" using
> geotools. I have used the following java code:
>
> ========================================================================
>
> CoordinateReferenceSystem sourceCRS = CRS.decode("epsg:3003"); //
> Gauss-Boaga Roma40
> CoordinateReferenceSystem targetCRS = CRS.decode("epsg:4326"); // WGS84
> MathTransform transform = CRS.findMathTransform(sourceCRS, targetCRS,
> false);
> GeometryFactory geometryFactory = new GeometryFactory(new
> PrecisionModel());
>
> Point point = geometryFactory.createPoint(new Coordinate(1664436,
> 5169278));
> Point targetPoint = (Point) JTS.transform(point, transform);
> System.out.println(targetPoint.getX());
> System.out.println(targetPoint.getY());
>
> ========================================================================
>
> but it looks like the resulting point has an error of about 10 meters
> both on lat and lon. The same happens with other
> points. All points in my small area (30km x 30km) have all the same error.
>
> I have converted the same source point using cs2cs and the result is
> much better (error < 1m)
>
> ========================================================================
> echo "1664436 5169278" | cs2cs +init=epsg:3003
> +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68 +to
> +init=epsg:4326 -f "%.8f"
> ========================================================================
>
> With others tools I have similar result like cs2cs
>
> Here a geojson with the resulting points
>
> { "type": "FeatureCollection", "features":[
> { "type": "Feature", "geometry": { "type": "Point", "coordinates":
> [11.14879437, 46.65668144] }, "properties": { "name": "cs2cs" } }
> ,{ "type": "Feature", "geometry": { "type": "Point", "coordinates":
> [11.148995971698204, 46.65658930259459] }, "properties": { "name":
> "geotools" } }
> ]}
>
> Why there is such error/offset in geotools conversion?
>
I was about to say "because of the different towgs84", but checking, we are
using
the peninsular values, the same you used for cs2cs.
So, it could be a bug, or a numerical issue (e.g., the calculus might be
arranged
in a different way to avoid losing precision along the way)
Cheers
Andrea
--
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