iOS MapKit - 每米點數

Question

我在MKOverlayView子類中繪製了一個圓。我有一個以米爲單位的半徑。如何將所述計量表轉換爲用於繪製drawMapRect的點（以該縮放比例）：zoomScale：inContext：？

Answer 1

看到標題：

助手：

// Conversion between distances and projected coordinates 
MK_EXTERN CLLocationDistance MKMetersPerMapPointAtLatitude(CLLocationDegrees latitude) NS_AVAILABLE(NA, 4_0); 
MK_EXTERN double MKMapPointsPerMeterAtLatitude(CLLocationDegrees latitude) NS_AVAILABLE(NA, 4_0); 

MK_EXTERN CLLocationDistance MKMetersBetweenMapPoints(MKMapPoint a, MKMapPoint b) NS_AVAILABLE(NA, 4_0); 

，並從MKOverlayView

// Convert screen points relative to this view to absolute MKMapPoints 
- (CGPoint)pointForMapPoint:(MKMapPoint)mapPoint; 
- (MKMapPoint)mapPointForPoint:(CGPoint)point; 

所以

double ppm = MKMapPointsPerMeterAtLatitude(centerCoordinate.latitude); 
MKMapPoint mkptLeftmost = ptCenter.x -= ppm; 
CGPoint ptLeftmost = [self pointForMapPoint:mkptLeftmost];