package com.vividsolutions.jtsexample.technique;
import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jts.io.WKTReader;
import java.util.*;
/**
* Shows a technique for identifying the location of self-intersections
* in a non-simple LineString.
*
* @version 1.7
*/
public class LineStringSelfIntersections {
public static void main(String[] args)
throws Exception
{
WKTReader rdr = new WKTReader();
LineString line1 = (LineString) (rdr.read("LINESTRING (0 0, 10 10, 20 20)"));
showSelfIntersections(line1);
LineString line2 = (LineString) (rdr.read("LINESTRING (0 40, 60 40, 60 0, 20 0, 20 60)"));
showSelfIntersections(line2);
}
public static void showSelfIntersections(LineString line)
{
System.out.println("Line: " + line);
System.out.println("Self Intersections: " + lineStringSelfIntersections(line));
}
public static Geometry lineStringSelfIntersections(LineString line)
{
Geometry lineEndPts = getEndPoints(line);
Geometry nodedLine = line.union(lineEndPts);
Geometry nodedEndPts = getEndPoints(nodedLine);
Geometry selfIntersections = nodedEndPts.difference(lineEndPts);
return selfIntersections;
}
public static Geometry getEndPoints(Geometry g)
{
List endPtList = new ArrayList();
if (g instanceof LineString) {
LineString line = (LineString) g;
endPtList.add(line.getCoordinateN(0));
endPtList.add(line.getCoordinateN(line.getNumPoints() - 1));
}
else if (g instanceof MultiLineString) {
MultiLineString mls = (MultiLineString) g;
for (int i = 0; i < mls.getNumGeometries(); i++) {
LineString line = (LineString) mls.getGeometryN(i);
endPtList.add(line.getCoordinateN(0));
endPtList.add(line.getCoordinateN(line.getNumPoints() - 1));
}
}
Coordinate[] endPts = CoordinateArrays.toCoordinateArray(endPtList);
return (new GeometryFactory()).createMultiPoint(endPts);
}
}