iOS MapKit - 每米点数

Question

我在MKOverlayView子类中绘制了一个圆。我有一个以米为单位的半径。如何将所述计量表转换为用于绘制drawMapRect的点（以该缩放比例）：zoomScale：inContext：？

Answer 1

看到标题：

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); 

，并从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];