检测多个多边形交叉点 (java)

Question

背景：该项目涉及在GIS环境中绘制区域。然后我需要找到一组多边形与另一组多边形的交集。我通过将 map-compatible 多边形转换为 Polygon2d (http://geom-java.sourceforge.net/api/math/geom2d/polygon/package-summary.html) 并使用交集方法查找相交多边形的顶点列表来实现此目的。

问题：除非在相同的两个多边形之间存在多个重叠区域，否则此方法有效。顶点列表是正确的，但我需要将列表分成每个单独的多边形。

第一张图片应该是这样的，第二张是实际生成的：

（忽略顶部区域。这是另一个错误的结果）

如何检测并纠正这种情况？

Answer 1

好吧，我想通了。我获取了相交多边形（蓝色）的顶点列表，遍历了每一对点，将两个原始多边形中的每条线段投射为 LineSegment2D 对象，并使用 .contains 方法检查每对点是否在其中一个线段。如果每对点不包含在一行中，则存在错误。

这是方法，但请记住，其中涉及多个专有类。

public static boolean noErrors(SurfacePolygonX p1, SurfacePolygonX p2, List<LatLon> list) {
    boolean allPointsInSamePolygon = true;

    //for each latlon jl in locations, cast jl and jl2 as points    
    for (int j = 0; j < list.size(); j++) {
        LatLon jl = list.get(j);
        LatLon jl2 = list.get((j == list.size() - 1) ? 0 : j + 1);
        Point2D pt = new Point2D(jl.longitude.degrees, jl.latitude.degrees);
        Point2D pt2 = new Point2D(jl2.longitude.degrees, jl2.latitude.degrees);

        List<LatLon> corners = p1.getCorners();

        boolean bothPointsInSameSegment = false;

        //for each latlon k selectedShape cast k and k+1 as 2lineseg
        for (int k = 0; k < corners.size(); k++) {
            LatLon kl = corners.get(k);
            LatLon kl2 = corners.get((k == corners.size() - 1) ? 0 : k + 1);

            LineSegment2D segment = new LineSegment2D(kl.longitude.degrees, kl.latitude.degrees, kl2.longitude.degrees, kl2.latitude.degrees);

            boolean segContainsP1 = segment.contains(pt);
            boolean segContainsP2 = segment.contains(pt2);

            System.out.println("selectedShape: segment "+k+" contains p"+j+":("+segContainsP1+") and p"+(j+1)+":("+segContainsP2+")");

            //check if each line contains the points.
            if (segContainsP1 && segContainsP2)
            {
                bothPointsInSameSegment = true;
            }

        }

        corners = p2.getCorners();
        //for each latlon k tempShape cast k and k+1 as 2lineseg
        for (int k = 0; k < corners.size(); k++) {
            LatLon kl = corners.get(k);
            LatLon kl2 = corners.get((k == corners.size() - 1) ? 0 : k + 1);

            LineSegment2D segment = new LineSegment2D(kl.longitude.degrees, kl.latitude.degrees, kl2.longitude.degrees, kl2.latitude.degrees);


            boolean segContainsP1 = segment.contains(pt);
            boolean segContainsP2 = segment.contains(pt2);

            System.out.println("intersectingShape: segment "+k+" contains p"+j+":("+segContainsP1+") and p"+(j+1)+":("+segContainsP2+")");

            //check if each line contains the points.
            if (segContainsP1 && segContainsP2)
            {
                bothPointsInSameSegment = true;
            }

        }

        if (!bothPointsInSameSegment) allPointsInSamePolygon = false;

    }

    //if both points are not in the same line, then theres a conflict
    return allPointsInSamePolygon;
}

Answer 2

您可以使用 JTS。

使用 LinearRing
使用intersection方法

简单代码示例：

// build polygon p1
LinearRing p1 = new GeometryFactory().createLinearRing(new Coordinate[]{new Coordinate(0,0), new Coordinate(0,10), new Coordinate(10,10), new Coordinate(10,0), new Coordinate(0,0)});
// build polygon p2
LinearRing p2 = new GeometryFactory().createLinearRing(new Coordinate[]{new Coordinate(5,5), new Coordinate(15,5), new Coordinate(15,15), new Coordinate(5,15), new Coordinate(5,5)});
// calculate intersecting points
Geometry intersectingPoints = p1.intersection(p2);
// print result
for(Coordinate c : intersectingPoints.getCoordinates()){
    System.out.println(c.toString());
}

输出是（如预期）：

(5.0, 10.0, NaN)
(10.0, 5.0, NaN)

检测多个多边形交叉点 (java)

Detecting multiple polygon intersections (java)

java

gis

intersection

polygon

concave