Question

MapKit的内置函数MKCoordinateRegionMakeWithDistance以米为单位将距离转换为MKCoordinateRegion：

func MKCoordinateRegionMakeWithDistance(
    _ centerCoordinate: CLLocationCoordinate2D, 
    _ latitudinalMeters: CLLocationDistance, 
    _ longitudinalMeters: CLLocationDistance) 
        -> MKCoordinateRegion

是否有一个倒数函数需要MKCoordinateRegion并给我纬度和经度？

Answer 1

MKCoordinateRegion给出中心（纬度和经度）和跨度（delta纬度和经度）。给定这些值，您可以确定纬度和经度区域边缘的位置。完成此操作后，您可以使用Haversine公式获取纬向和纵向距离，并且您已经知道中心。实际上，CLLocation具有函数distanceFromLocation:(const CLLocation *)location，应使用该函数来避免直接实现公式。

Answer 2

基于Adam H.的想法，这是我在Swift 4中使用单元测试的实现：

extension MKCoordinateRegion {
    /// middle of the south edge
    var south: CLLocation {
        return CLLocation(latitude: center.latitude - span.latitudeDelta / 2, longitude: center.longitude)
    }
    /// middle of the north edge
    var north: CLLocation {
        return CLLocation(latitude: center.latitude + span.latitudeDelta / 2, longitude: center.longitude)
    }
    /// middle of the east edge
    var east: CLLocation {
        return CLLocation(latitude: center.latitude, longitude: center.longitude + span.longitudeDelta / 2)
    }
    /// middle of the west edge
    var west: CLLocation {
        return CLLocation(latitude: center.latitude, longitude: center.longitude - span.longitudeDelta / 2)
    }
    /// distance between south and north in meters. Reverse function for MKCoordinateRegionMakeWithDistance
    var latitudinalMeters: CLLocationDistance {
        return south.distance(from: north)
    }
    /// distance between east and west in meters. Reverse function for MKCoordinateRegionMakeWithDistance
    var longitudinalMeters: CLLocationDistance {
        return east.distance(from: west)
    }
}

单元测试：

func testMKCoordinateRegionMakeWithDistance() {
    // arbitrary parameters
    let center = CLLocationCoordinate2DMake(49, 9)
    let latitudinalMeters: CLLocationDistance = 1000
    let longitudinalMeters: CLLocationDistance = 2000

    let region = MKCoordinateRegionMakeWithDistance(center, latitudinalMeters, longitudinalMeters)
    XCTAssertEqual(latitudinalMeters, round(region.latitudinalMeters*100)/100)
    XCTAssertEqual(longitudinalMeters, round(region.longitudinalMeters*100)/100)
}

测试设计：

对经纬度使用不同的数字来查找变量混合在一起的错误
四舍五入检查大约5个有效的小数位

MKCoordinateRegionMakeWithDistance的反向功能？

2 个答案: