Question

我试图确定一个点是否位于多边形内部。我使用this website中的以下（针对Swift修改）算法：

func contains(polygon: [Point], test: Point) -> Bool {
    let count = polygon.count
    var i: Int, j: Int
    var contains = false
    for (i = 0, j = count - 1; i < count; j = i++) {
        if ( ((polygon[i].y >= test.y) != (polygon[j].y >= test.y)) &&
            (test.x <= (polygon[j].x - polygon[i].x) * (test.y - polygon[i].y) /
                (polygon[j].y - polygon[i].y) + polygon[i].x) ) {
                    contains = !contains;
        }
    }
    return contains;
}

但是，当具有以下坐标的简单多边形：(x: 0, y: 40), (x: 0, y: 0), (x: 20, y: 0), (x: 20, y: 20), (x: 40, y: 20), (x: 40, y: 40)并检查点(x: 30, y: 20)时，结果为true，因为if {语句在{{true时计算为i 1}}和j分别为5和4（(x: 40, y: 40)和(x: 40, y: 20)），但该点仅位于多边形的边框处。如果该点实际位于 in 多边形中，该函数实际上应仅评估true。感谢您对算法的任何帮助或改进/调整！

Answer 1

如果这是针对iOS应用程序，请将您的多边形转换为UIBezierPath，然后使用函数containtsPoint()验证您的点是否位于bezierpath

示例（iOS）：

func contains(polygon: [CGPoint], test: CGPoint) -> Bool {
        if polygon.count <= 1 {
            return false //or if first point = test -> return true
        }

        var p = UIBezierPath()
        let firstPoint = polygon[0] as CGPoint

        p.moveToPoint(firstPoint)

        for index in 1...polygon.count-1 {
            p.addLineToPoint(polygon[index] as CGPoint)
        }

        p.closePath()

       return p.containsPoint(test)
    }

Answer 2

也适合我，所以我不知道问题在哪里

我还使用了一个轻微的修改版本来使用swift迭代器：

func contains(polygon: [Point], test: Point) -> Bool {

  var pJ=polygon.last!
  var contains = false
  for pI in polygon {
    if ( ((pI.y >= test.y) != (pJ.y >= test.y)) &&
    (test.x <= (pJ.x - pI.x) * (test.y - pI.y) / (pJ.y - pI.y) + pI.x) ){
          contains = !contains
    }
    pJ=pI
  }
  return contains
}

以下是您在游乐场中使用数组示例的结果：

contains(poly,Point(x:40,y:40))   -> true
contains(poly,Point(x:30,y:20))   -> false
contains(poly,Point(x:40,y:20))   -> true
contains(poly,Point(x:1,y:1))     -> true

Answer 3

extension MKPolygon {
    func contain(coor: CLLocationCoordinate2D) -> Bool {
        let polygonRenderer = MKPolygonRenderer(polygon: self)
        let currentMapPoint: MKMapPoint = MKMapPointForCoordinate(coor)
        let polygonViewPoint: CGPoint = polygonRenderer.point(for: currentMapPoint)
        return polygonRenderer.path.contains(polygonViewPoint)
    }
}

Answer 4

这是PNPoly算法的改进实现。我用它，它工作正常。

func isPointInsidePolygon(polygon: [CGPoint], test:CGPoint) -> Bool {
 var  i:Int, j:Int = polygon.count - 1
 var  contains = false

 for (i = 0; i < polygon.count; i++) {
    if (((polygon[i].y < test.y && polygon[j].y >= test.y) || (polygon[j].y < test.y && polygon[i].y >= test.y))
        && (polygon[i].x <= test.x || polygon[j].x <= test.x)) {
            contains ^= (polygon[i].x + (test.y - polygon[i].y) / (polygon[j].y - polygon[i].y) * (polygon[j].x - polygon[i].x) < test.x)
    }

    j = i
 }

 return contains
}

进一步查询：http://alienryderflex.com/polygon/

Answer 5

这是javascript代码（易于理解，你可以在swift上重写）。它对我来说非常适合，几乎100％，即精确度很高。

你的解决方案精度不高。

function pointIsInPoly(v, polygon) {
    var edge_error = 1.192092896e-07; // epsilon i.e ~0.000000192
    var x = 0;
    var y = 1;
    var i, j;
    var r = false;
    for (i = 0, j = polygon.length - 1; i < polygon.length; j = i++)
    {
        var pi = polygon[i];
        var pj = polygon[j];
        if (Math.abs(pi[y] - pj[y]) <= edge_error && Math.abs(pj[y] - v[y]) <= edge_error && (pi[x] >= v[x]) != (pj[x] >= v[x]))
        {   
            return true;
        }

        if ((pi[y] > v[y]) != (pj[y] > v[y]))
        {
            var c = (pj[x] - pi[x]) * (v[y] - pi[y]) / (pj[y] - pi[y]) + pi[x];
            if (Math.abs(v[x] - c) <= edge_error)
            {
                return true;
            }
            if (v[x] < c)
            {
                r = !r;
            }
        }
    }
    return r;
}

检查点是否在简单多边形内

5 个答案: