Re: [Jts-topo-suite-user] robust distance computation

[Tomas Fa <tof...@gm...>]

Great, thanks!

/Tomas

On Tue, Aug 21, 2012 at 4:32 PM, Martin Davis <mtn...@te...> wrote:

>  There's a fix for this issue now in SVN.
>
> When I took a close look at the distanceLineLine method I realized there
> was some opportunity for some performance and code clarity improvements, so
> those are included as well.
>
>
> On 8/20/2012 1:24 AM, Tomas Fa wrote:
>
> Hi,
> I have encountered a situation when the distance computed between two
> polygons is wrong.
> My conclusion is that CGAlgorithms.distanceLineLine is to blame. The
> documentation also
> states that this method is non-robust. The program below reproduces this
> case for two lines instead of two polygons. Does JTS provide a robust
> version of the distance algorithm?
>
> Thanks,
> Tomas
>
>         WKTReader reader = new WKTReader();
>         LineString lineStringA =
>                 (LineString) reader.read("LINESTRING (0.0 0.0, 9.9 1.4)");
>         LineString lineStringB =
>                 (LineString) reader.read("LINESTRING (11.88 1.68, 21.78
> 3.08)");
>
>         double dist = lineStringA.distance(lineStringB);
>         double distCGAlgorithms =
> CGAlgorithms.distanceLineLine(lineStringA.getStartPoint().getCoordinate(),
>
> lineStringA.getEndPoint().getCoordinate(),
>
> lineStringB.getStartPoint().getCoordinate(),
>
> lineStringB.getEndPoint().getCoordinate());
>
>         System.out.println("dist(CGAlgorithms): " + distCGAlgorithms);
>         System.out.println("dist(Geometry): " + distCGAlgorithms);
>
>         LineIntersector lineIntersector = new RobustLineIntersector();
>
> lineIntersector.computeIntersection(lineStringA.getStartPoint().getCoordinate(),
>
> lineStringA.getEndPoint().getCoordinate(),
>
> lineStringB.getStartPoint().getCoordinate(),
>
> lineStringB.getEndPoint().getCoordinate());
>
>         assert lineIntersector.getIntersectionNum() == 0;
>
>         double endpointDist1 =
> lineStringA.getStartPoint().distance(lineStringB);
>         double endpointDist2 =
> lineStringA.getEndPoint().distance(lineStringB);
>         double endpointDist3 =
> lineStringB.getStartPoint().distance(lineStringA);
>         double endpointDist4 =
> lineStringB.getEndPoint().distance(lineStringA);
>
>         assert dist > 0.0 : "No intersections but distance is " + dist+
> "\n"
>                             +"Point distance 1: " + endpointDist1 + "\n"
>                 +"Point distance 2: " + endpointDist2 + "\n"
>                 +"Point distance 3: " + endpointDist3 + "\n"
>                 +"Point distance 4: " + endpointDist4 + "\n";
>
>
>
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