MKMapView - 如何計算當前正在查看的平方英里

Question

要使用接受northEast和SouthWest座標的各種API用作「視口」，某些API對於搜索具有最大平方英里限制。

我想計算當前MKMapView縮放級別顯示的平方英里數。

Answer 1

這裏是解決方案：

- (float)numSquareMiles 
{ 
    CLLocationCoordinate2D northEast, southWest; 
    northEast = [mapView convertPoint:CGPointMake(mapView.frame.size.width, 0) toCoordinateFromView:mapView]; 
    southWest = [mapView convertPoint:CGPointMake(0, mapView.frame.size.height) toCoordinateFromView:mapView]; 


    float distanceLatInDegrees = northEast.latitude - southWest.latitude; 
    float numLatMiles = 69.172 * distanceLatInDegrees; 

    float distanceLonInDegrees = northEast.longitude - southWest.longitude; 
    float numLonMiles = 69.172 * distanceLonInDegrees; 

    float numSquareMiles = numLatMiles*numLonMiles; 

    return numSquareMiles; 
}