Re: [Jts-topo-suite-user] linear referencing problem

[Michaël M. <mic...@fr...>]

Hi Martin,

After much time spent to understand the rational behind LinearIterator and
LinearLocation, I get a solution. I'm not completely satisfied by the 
design,
because it happens lately in the process, is based on a naive if/else 
solution,
and has to be duplicated in two classes...but at least, it seems to pass 
all the
unit tests.


First the test case which makes the current version fail :
AbstractIndexedLineTest :
public void testOffsetEndPoint()
   {
     runOffsetTest("LINESTRING (0 0, 13 13, 20 20)", "POINT(20 20)", 
0.0, "POINT (20 20)");
     runOffsetTest("LINESTRING (0 0, 10 0, 20 0)", "POINT(20 0)", 1.0, 
"POINT (20 1)");
     runOffsetTest("LINESTRING (0 0, 20 0)", "POINT(10 0)", 1.0, "POINT 
(10 1)"); // point on last segment
     runOffsetTest("MULTILINESTRING ((0 0, 10 0), (10 0, 20 0))", 
"POINT(10 0)", -1.0, "POINT (10 -1)");
     runOffsetTest("MULTILINESTRING ((0 0, 10 0), (10 0, 20 0))", 
"POINT(20 0)", 1.0, "POINT (20 1)");
   }

Now the fix for LengthIndexedLine
public Coordinate extractPoint(double index, double offsetDistance)
   {
     LinearLocation loc = LengthLocationMap.getLocation(linearGeom, index);
     LineSegment segment = loc.getSegment(linearGeom);
     if (loc.isEndpoint(linearGeom)) {
       return segment.pointAlongOffset(1.0, offsetDistance);
     } else {
       return segment.pointAlongOffset(loc.getSegmentFraction(), 
offsetDistance);
     }
   }

And the same for LocationIndexedLine
public Coordinate extractPoint(LinearLocation index, double offsetDistance)
   {
     LineSegment segment = index.getSegment(linearGeom);
     if (index.isEndpoint(linearGeom)) {
       return segment.pointAlongOffset(1.0, offsetDistance);
     } else {
       return segment.pointAlongOffset(index.getSegmentFraction(), 
offsetDistance);
     }
   }

Hope that helps,

Michaël

> Hi Martin,
>
> I found a small problem in linear referencing package (JTS 1.13).
>
> If I extract a point at distance 100 on LINESTRING(0 0, 100 0)
> - I get 100, 0 with extractPoint(100) : test in testbuilder
> - I get 0, 0 with extractPoint(100, 0) : test through OpenJUMP
>
> The result is not the same with the single parameter method
> and the two parameters method.
>
> I think the problem comes from LengthLocationMap#getLocationForward
> It computes the following LinearLocation (which seems OK so far)
> getSegmentIndex = 1 (virtual second segment)
> getSegmentFraction = 0.0 (first point)
>
> but in this particular case, LinearLocation#getSegment() returns
> segment n-1 and not segment n (probably needed to be able to compute
> offset).
> To be consistent , returned LinearLocation should probably have
> segmentIndex = 0
> segmentFraction = 1.0
>
> Not sure if the problem is in LengthLocationMap#getLocationForward itself
> or in LinearIterator#isEndOfLine() which is used by the former and returns
> false if (componentIndex >= numLines)
> or maybe I missed the point,
>
> thanks for your help
>
> Michaël
>
>
> ------------------------------------------------------------------------------
> October Webinars: Code for Performance
> Free Intel webinars can help you accelerate application performance.
> Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from
> the latest Intel processors and coprocessors. See abstracts and register >
> http://pubads.g.doubleclick.net/gampad/clk?id=60135031&iu=/4140/ostg.clktrk
> _______________________________________________
> Jts-topo-suite-user mailing list
> Jts...@li...
> https://lists.sourceforge.net/lists/listinfo/jts-topo-suite-user
>
>