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
>
>
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