ios - 如何在iOS中获取MKPolygon的区域

Question

如何在iOS中获取MKPolygon或MKOverlay的区域？

我已经能够将“多边形”分解为三角形，并进行一些数学运算以获得面积。但是，不适用于不规则多边形。

我当时正在考虑做类似“更复杂的案例”的事情:http://www.mathopenref.com/coordpolygonarea2.html

我希望MapKit有一个更简单的解决方案。

谢谢，
提姆

Answer 1

这是我正在使用的实现。

#define kEarthRadius 6378137
@implementation MKPolygon (AreaCalculation)

- (double) area {
  double area = 0;
  NSMutableArray *coords = [[self coordinates] mutableCopy];
  [coords addObject:[coords firstObject]];

  if (coords.count > 2) {
    CLLocationCoordinate2D p1, p2;
    for (int i = 0; i < coords.count - 1; i++) {
      p1 = [coords[i] MKCoordinateValue];
      p2 = [coords[i + 1] MKCoordinateValue];
      area += degreesToRadians(p2.longitude - p1.longitude) * (2 + sinf(degreesToRadians(p1.latitude)) + sinf(degreesToRadians(p2.latitude)));
    }

    area = - (area * kEarthRadius * kEarthRadius / 2);
  }
  return area;
}
- (NSArray *)coordinates {
  NSMutableArray *points = [NSMutableArray arrayWithCapacity:self.pointCount];
  for (int i = 0; i < self.pointCount; i++) {
    MKMapPoint *point = &self.points[i];
    [points addObject:[NSValue valueWithMKCoordinate:MKCoordinateForMapPoint(* point)]];
  }
  return points.copy;
}

double degreesToRadians(double radius) {
  return radius * M_PI / 180;
}

在Swift 3中

let kEarthRadius = 6378137.0

extension MKPolygon {
    func degreesToRadians(_ radius: Double) -> Double {
        return radius * .pi / 180.0
    }

    func area() -> Double {
        var area: Double = 0

        var coords = self.coordinates()
        coords.append(coords.first!)

        if (coords.count > 2) {
            var p1: CLLocationCoordinate2D, p2: CLLocationCoordinate2D
            for i in 0..<coords.count-1 {
                p1 = coords[i]
                p2 = coords[i+1]
                area += degreesToRadians(p2.longitude - p1.longitude) * (2 + sin(degreesToRadians(p1.latitude)) + sin(degreesToRadians(p2.latitude)))
            }
            area = abs(area * kEarthRadius * kEarthRadius / 2)
        }

        return area
    }

    func coordinates() -> [CLLocationCoordinate2D] {
        var points: [CLLocationCoordinate2D] = []
        for i in 0..<self.pointCount {
            let point = self.points()[i]
            points.append(MKCoordinateForMapPoint(point))
        }
        return Array(points)
    }
}