iphone - how to find current zoom level of MKMapView?

Question

I want to know the current zoom level of MKMapView in iphone programming, how can I do that? Actually I have one app, that is taking few arguments(Radius from center to corner of MKMapView) are returning the store details in that are, when I am on MKMapView, the radius is very high and it changes when Radius is smaller, so I want to know the zoom level and setup my webservice according to that, How can I get zoom level of current MKMapView visible area?

Answer 1

I created very simple helper subclass for it:

#define MERCATOR_RADIUS 85445659.44705395
#define MAX_GOOGLE_LEVELS 20

@interface MKMapView (ZoomLevel)
- (double)getZoomLevel;
@end

@implementation MKMapView (ZoomLevel)

- (double)getZoomLevel
{
    CLLocationDegrees longitudeDelta = self.region.span.longitudeDelta;
    CGFloat mapWidthInPixels = self.bounds.size.width;
    double zoomScale = longitudeDelta * MERCATOR_RADIUS * M_PI / (180.0 * mapWidthInPixels);
    double zoomer = MAX_GOOGLE_LEVELS - log2( zoomScale );
    if ( zoomer < 0 ) zoomer = 0;
//  zoomer = round(zoomer);
    return zoomer;
}

@end