Question

所以我正在编写一个获取与多边形相交的所有点的方法。

这是我的Polygon。

Point point = new Point(1, 1);
points.add(point);
point = new Point(99, 99);

points.add(point);
point = new Point(199, 1);
points.add(point);
polygon = new Polygon(points);

这是我的测试用例。

List<Point> expected = new ArrayList<Point>();
Point p = new Point();
p.setX(50);
p.setY(50);
expected.add(p);

Point start = new Point(1, 99);
Point end = new Point(99, 1);
Line aLine = new Line(start, end);
List<Point> intersection = new ArrayList<>(polygon.getIntersections(aLine)); //Normal Case

assertNotNull(intersection);
assertEquals(expected,intersection);

我认为这是非常自我解释的，但Point是一个有x，y，z值的类，Line只有4个点，前两个是一个点，第二个2点是另一个点，它们只是连接。

这是获取所有交叉点的方法。

public List<Point> getIntersections(Crossable aLine) {
    List<Point> listOfIntersections = new ArrayList<Point>();
    Point intersectedPoint = new Point();
    for(int i = 0; i < this.points.size()-1; i++) {
        Point firstPoint = this.points.get(i);
        for(int j = i + 1; j < this.points.size(); j++) {
            Point secondPoint = this.points.get(j);

            Line2D line1 = new Line2D.Double(
                firstPoint.getX(), firstPoint.getY(),
                secondPoint.getX(), secondPoint.getY()
            );
            Line2D line2 = new Line2D.Double(
                ((Line) aLine).getStart().getX(),((Line) aLine).getStart().getY(),
                ((Line) aLine).getEnd().getX(),  ((Line) aLine).getEnd().getY()
            );
            boolean result = line2.intersectsLine(line1);
            if(!result) {

            }
            else {
                final double x1, y1, x2,y2, x3,y3, x4,y4;

                x1 = firstPoint.getX();
                y1 = firstPoint.getY();
                x2 = secondPoint.getX();
                y2 = secondPoint.getY();
                x3 = ((Line) aLine).getStart().getX();
                y3 = ((Line) aLine).getStart().getY();
                x4 = ((Line) aLine).getEnd().getX();
                y4 = ((Line) aLine).getEnd().getY();

                double denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);
                if (denom == 0.0) { // Lines are parallel.

                }
                double ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denom;
                double ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denom;
                if (ua >= 0.0f && ua <= 1.0f && ub >= 0.0f && ub <= 1.0f) {
                    // Get the intersection point.
                    intersectedPoint.setX(x1 + ua*(x2 - x1));
                    intersectedPoint.setY(y1 + ua*(y2 - y1));
                    listOfIntersections.add(intersectedPoint);
                }
            }
        }
    }

    if(listOfIntersections.size() == 0) {
        return null;
    }
    return listOfIntersections;
}

由于某种原因而不是返回＆lt; 50,50＆gt;这是它返回的多边形的正确交点＆lt; 99,1＆gt;和＆lt; 99,1＆gt;有什么建议吗？感谢。

Answer 1

涉及两点交叉的计算是错误的。您可以查看以下链接以查找两条给定线的交点： https://www.geeksforgeeks.org/program-for-point-of-intersection-of-two-lines/

获取与多边形相交的所有点？

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