自定义半径以米为单位的MKOverlay

Question

我通过创建一个符合NSObject协议的MKOverlay子类和一个MKOverlayPathRenderer子类来创建一个自定义覆盖。我的目标是创建一个循环覆盖，它锚定在MKMapView上的用户位置上，而且我的工作非常好。每当设置了覆盖上的坐标时，我的渲染器就会使用键值观察，使它所绘制的路径无效，然后重新绘制。

我遇到的问题是，我希望圆的半径以米为单位，但我不认为我在做正确的数学运算，或者我遗漏了一些东西。我在下面发布了覆盖对象和呈现器的源代码(渲染器的接口中没有任何内容)。举个例子，我把半径设定在200米，但在地图上，它只显示为10米左右。有人知道怎么解决吗？

//Custom Overlay Object Interface
@import Foundation;
@import MapKit;
@interface CustomRadiusOverlay : NSObject <MKOverlay>

+ (id)overlayWithCoordinate:(CLLocationCoordinate2D)coordinate radius:(CLLocationDistance)radius;

@property (nonatomic) CLLocationCoordinate2D coordinate;
@property (nonatomic) MKMapRect boundingMapRect;
@property (nonatomic) CLLocationDistance radius;

@end

//Custom overlay
#import "CustomRadiusOverlay.h"

@implementation LFTRadiusOverlay

+ (id)overlayWithCoordinate:(CLLocationCoordinate2D)coordinate radius:(CLLocationDistance)radius{
CustomRadiusOverlay* overlay = [LFTRadiusOverlay new];
    overlay.coordinate = coordinate;
    overlay.radius = radius;
    return overlay;
}

- (MKMapRect)boundingMapRect{
    MKMapPoint upperLeft = MKMapPointForCoordinate(self.coordinate);
    MKMapRect bounds = MKMapRectMake(upperLeft.x, upperLeft.y, self.radius*2, self.radius*2);
    return bounds;
}

- (void)setCoordinate:(CLLocationCoordinate2D)coordinate{
    _coordinate = coordinate;
    self.boundingMapRect = self.boundingMapRect;
}

@end


#import "CustomOverlayRadiusRenderer.h"
#import "CustomRadiusOverlay.h"

@interface CustomOverlayRadiusRenderer()

@property (nonatomic) CustomRadiusOverlay* circleOverlay;

@end

@implementation CustomOverlayRadiusRenderer

- (id)initWithOverlay:(id<MKOverlay>)overlay{
    self = [super initWithOverlay:overlay];
    if(self){
        _circleOverlay = (LFTRadiusOverlay*)overlay;
        [_circleOverlay addObserver:self forKeyPath:@"coordinate" options:NSKeyValueObservingOptionNew context:NULL];
        self.fillColor = [UIColor redColor];
        self.alpha = .7f;
    }
    return self;
}

- (void)createPath{
    CGMutablePathRef path = CGPathCreateMutable();
    MKMapPoint mapPoint = MKMapPointForCoordinate(self.circleOverlay.coordinate);
    CGPoint point = [self pointForMapPoint:mapPoint];
    CGPathAddArc(path, NULL, point.x, point.y, self.circleOverlay.radius, 0, kDegreesToRadians(360), YES);
    self.path = path;
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    [self invalidatePath];
}
@end

Answer 1

您可以绘制米(作为半径)，但需要在MapPoints中指定所有内容。

因此，转换单位：

~~ mapPoints = meters * MKMapPointsPerMeterAtLatitude(coordinate.latitude)