我想知道iPhone屏幕上可见区域的半径,因为当我缩放时,可见区域会发生变化,所以我想知道那个特定区域的半径,我该怎么做?
我想知道iPhone屏幕上可见区域的半径,因为当我缩放时,可见区域会发生变化,所以我想知道那个特定区域的半径,我该怎么做?
所需的不是半径。
你需要使用mapView中的region参数。
查看苹果文档,从那里可以很清楚地了解。
通过这个教程,它会帮助你很多。
具体来说,你需要设置类似于这样的内容...
MKCoordinateSpan span = [self coordinateSpanWithMapView:self centerCoordinate:centerCoordinate andZoomLevel:zoomLevel];
MKCoordinateRegion region = MKCoordinateRegionMake(centerCoordinate, span);
[self setRegion:region animated:animated];
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 :)
- (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);
}