23

我有一组构建形状的 X 和 Y 点，我需要知道一个对象是否在其中，它的计算是什么？

X 和 Y 坐标示例：

522.56055 2389.885
544.96 2386.3406
554.18616 2369.2385
535.21814 2351.396
497.5552 2355.8396

我对数学不是很好:(所以我希望能得到一些支持来理解它是如何完成的。

到目前为止我所拥有但似乎不太可靠的示例：

private boolean isInsideShape(Zone verifyZone, Position object)
{
    int corners = verifyZone.getCorners();
    float[] xCoords = verifyZone.getxCoordinates();
    float[] yCoords = verifyZone.getyCoordinates();

    float x = object.getX();
    float y = object.getY();
    float z = object.getZ();

    int i, j = corners - 1;
    boolean inside = false;

    for(i = 0; i < corners; i++)
    {
        if(yCoords[i] < y && yCoords[j] >= y || yCoords[j] < y && yCoords[i] >= y)
            if(xCoords[i] + (y - yCoords[i]) / (yCoords[j] - yCoords[i]) * (xCoords[j] - xCoords[i]) < x)
                inside = !inside;
        j = i;
    }

    return inside;
}
4

2 回答 2

44

你可以从这里开始：http ://en.wikipedia.org/wiki/Point_in_polygon

您还可以查看JTS Topology Suite。并且特别使用这个功能。

编辑：这是使用 JTS 的示例：

import java.util.ArrayList;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.GeometryFactory;
import com.vividsolutions.jts.geom.LinearRing;
import com.vividsolutions.jts.geom.Point;
import com.vividsolutions.jts.geom.Polygon;
import com.vividsolutions.jts.geom.impl.CoordinateArraySequence;

public class GeoTest {

  public static void main(final String[] args) {

    final GeometryFactory gf = new GeometryFactory();

    final ArrayList<Coordinate> points = new ArrayList<Coordinate>();
    points.add(new Coordinate(-10, -10));
    points.add(new Coordinate(-10, 10));
    points.add(new Coordinate(10, 10));
    points.add(new Coordinate(10, -10));
    points.add(new Coordinate(-10, -10));
    final Polygon polygon = gf.createPolygon(new LinearRing(new CoordinateArraySequence(points
        .toArray(new Coordinate[points.size()])), gf), null);

    final Coordinate coord = new Coordinate(0, 0);
    final Point point = gf.createPoint(coord);

    System.out.println(point.within(polygon));

  }

}

这是使用 AWT 的示例（它更简单，是 Java SE 的一部分）：

import java.awt.Polygon;

public class JavaTest {

  public static void main(final String[] args) {

    final Polygon polygon = new Polygon();
    polygon.addPoint(-10, -10);
    polygon.addPoint(-10, 10);
    polygon.addPoint(10, 10);
    polygon.addPoint(10, -10);

    System.out.println(polygon.contains(0, 0));

  }

}
于 2011-03-03T00:31:47.440 回答
1

我一直这样做：

Pick a point you know to be outside the shape.
Make a line between that point and the point you're trying to find whether it's inside the shape or not.
Count the number of sides of the shape the line crosses. 

If the count is odd, the point is inside the shape.
If the count is even, the point is outside the shape.
于 2011-03-03T00:56:21.137 回答