在MKMapView中计算MKPolygon的面积 [英] Calculate area of MKPolygon in an MKMapView

问题描述

我只是不知道如何计算MKMapView上的面积.解决这个问题的人了吗?

I just don't know how to calculate the area on the MKMapView. Anyone who has solved this problem yet?

这是我的代码，但是返回的太多了:

This is my code, but it returns way too much:

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

    if templocations.count > 2 {
        var p1,p2:CLLocationCoordinate2D

        for var i = 0; i < templocations.count - 1; i++ {
            var loc = templocations[i] as CLLocation
            p1 = CLLocationCoordinate2D(latitude: loc.coordinate.latitude, longitude: loc.coordinate.longitude)

            loc = templocations[i+1] as CLLocation
            p2 = CLLocationCoordinate2D(latitude: loc.coordinate.latitude, longitude: loc.coordinate.longitude)

            var sinfunc: Float = (2 + sinf(Float(degreeToRadiant(p1.latitude))) + sinf(Float(degreeToRadiant(p2.latitude))))

            area += degreeToRadiant(p2.longitude - p1.longitude) * Double(sinfunc)
        }
        area = area * kEarthRadius * kEarthRadius / 2;
    }
    return area
}

推荐答案

Stefan的答案已在 Swift 5.0 中实现:

Stefan's answer implemented in Swift 5.0 :

import MapKit
let kEarthRadius = 6378137.0

func radians(degrees: Double) -> Double {
    return degrees * .pi / 180
}

func regionArea(locations: [CLLocationCoordinate2D]) -> Double {

    guard locations.count > 2 else { return 0 }
    var area = 0.0

    for i in 0..<locations.count {
        let p1 = locations[i > 0 ? i - 1 : locations.count - 1]
        let p2 = locations[i]

        area += radians(degrees: p2.longitude - p1.longitude) * (2 + sin(radians(degrees: p1.latitude)) + sin(radians(degrees: p2.latitude)) )
    }
    area = -(area * kEarthRadius * kEarthRadius / 2)
    return max(area, -area) // In order not to worry about is polygon clockwise or counterclockwise defined.
}

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