如何找到可见MKMapView可见屏幕区域的半径？

Question

我想知道iPhone屏幕中可见区域的半径，因为我会缩小和放大可见区域会发生变化，所以我想知道该特定区域的半径，我该怎么做？

Answer 1

它不是所需的半径。

您需要使用mapView 中的region 参数。

查一下苹果文档，里面说的很清楚了。

完成本教程。它会对你有很大帮助

icode博客mapkit演示

具体来说，你需要设置这样的东西..

MKCoordinateSpan span = [self coordinateSpanWithMapView:self centerCoordinate:centerCoordinate andZoomLevel:zoomLevel];
MKCoordinateRegion region = MKCoordinateRegionMake(centerCoordinate, span);
[self setRegion:region animated:animated];

其中span可以计算为

- (MKCoordinateSpan)coordinateSpanWithMapView:(MKMapView *)mapView
                         centerCoordinate:(CLLocationCoordinate2D)centerCoordinate
                             andZoomLevel:(NSUInteger)zoomLevel
{
// convert center coordiate to pixel space
double centerPixelX = [self longitudeToPixelSpaceX:centerCoordinate.longitude];
double centerPixelY = [self latitudeToPixelSpaceY:centerCoordinate.latitude];

// determine the scale value from the zoom level
NSInteger zoomExponent = 20 - zoomLevel;
double zoomScale = pow(2, zoomExponent);

// scale the map’s size in pixel space
CGSize mapSizeInPixels = mapView.bounds.size;
double scaledMapWidth = mapSizeInPixels.width * zoomScale;
double scaledMapHeight = mapSizeInPixels.height * zoomScale;

// figure out the position of the top-left pixel
double topLeftPixelX = centerPixelX - (scaledMapWidth / 2);
double topLeftPixelY = centerPixelY - (scaledMapHeight / 2);

// find delta between left and right longitudes
CLLocationDegrees minLng = [self pixelSpaceXToLongitude:topLeftPixelX];
CLLocationDegrees maxLng = [self pixelSpaceXToLongitude:topLeftPixelX + scaledMapWidth];
CLLocationDegrees longitudeDelta = maxLng - minLng;

// find delta between top and bottom latitudes
CLLocationDegrees minLat = [self pixelSpaceYToLatitude:topLeftPixelY];
CLLocationDegrees maxLat = [self pixelSpaceYToLatitude:topLeftPixelY + scaledMapHeight];
CLLocationDegrees latitudeDelta = -1 * (maxLat - minLat);

// create and return the lat/lng span
MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
return span;
}

干杯:)

Answer 2

我可能误解了这个问题，但它不是那么简单吗：

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated {
    CGFloat latD = mapView.region.span.latitudeDelta;
    CGFloat lngD = mapView.region.span.longitudeDelta;
    NSLog(@"This is the latitude delta of the visible map: %f", latD);
    NSLog(@"This is the longitude delta of the visible map: %f", lngD);
}