iOS 缩放等级 Set the Zoom Level of an MKMapView

标签：Set Level double self 缩放 zoom zoomLevel MERCATOR level

Set the Zoom Level of an MKMapView

http://troybrant.net/blog/2010/01/set-the-zoom-level-of-an-mkmapview/

If you have ever built a web application using the Google Maps API, you are likely intimately familiar with this line of code:

map.setCenter( new google.maps. LatLng( 37.4419, - 122. 1419), 13);

setCenterMapKit on the iPhone does not include a way to set the zoom level. Instead, the zoom level is set implicitly by defining the MKCoordinateRegionMKMapView explicitly. In this post, I’ll give you code you can drop into your own projects and start using immediately. My next post will detail exactly how it works.

The Code

MKMapView

// MKMapView+ZoomLevel.h

#import <MapKit/MapKit.h>

@interface

void)setCenterCoordinate:(CLLocationCoordinate2D)centerCoordinate
zoomLevel:(NSUInteger)zoomLevel
animated:(BOOL)animated;

@end

// MKMapView+ZoomLevel.m 
   
 
#import "MKMapView+ZoomLevel.h"
#define MERCATOR_OFFSET 268435456
#define MERCATOR_RADIUS 85445659.44705395@implementation
#pragma mark -
#pragma mark Map conversion methodsdouble)longitudeToPixelSpaceX:(double)longitude
 {
     return round(MERCATOR_OFFSET + MERCATOR_RADIUS * longitude * M_PI / 180.0);
 }double)latitudeToPixelSpaceY:(double)latitude
 {
     return round(MERCATOR_OFFSET - MERCATOR_RADIUS * logf((1 + sinf(latitude * M_PI / 180.0)) / (1 - sinf(latitude * M_PI / 180.0))) / 2.0);
 }double)pixelSpaceXToLongitude:(double)pixelX
 {
     return ((round(pixelX) - MERCATOR_OFFSET) / MERCATOR_RADIUS) * 180.0 / M_PI;
 }double)pixelSpaceYToLatitude:(double)pixelY
 {
     return (M_PI / 2.0 - 2.0 * atan(exp((round(pixelY) - MERCATOR_OFFSET) / MERCATOR_RADIUS))) * 180.0 / M_PI;
 }#pragma mark -
#pragma mark Helper methodsMKCoordinateSpan)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;
 }#pragma mark -
#pragma mark Public methodsvoid)setCenterCoordinate:(CLLocationCoordinate2D)centerCoordinate
     zoomLevel:(NSUInteger)zoomLevel
     animated:(BOOL)animated
 {
     // clamp large numbers to 28
     zoomLevel = MIN(zoomLevel, 28);
     
     // use the zoom level to compute the region
     MKCoordinateSpan span = [self coordinateSpanWithMapView:self centerCoordinate:centerCoordinate andZoomLevel:zoomLevel];
     MKCoordinateRegion region = MKCoordinateRegionMake(centerCoordinate, span);
     
     // set the region like normal
     [self setRegion:region animated:animated];
 }@end

If you’re wondering why this works, check out my next post where I describe in gruesome detail the math behind the code.

how it works, just that it does

Test the Code

MKMapView

// ZoomLevelTestViewController.m 
   
 
#import "MKMapView+ZoomLevel.h"
#define GEORGIA_TECH_LATITUDE 33.777328
#define GEORGIA_TECH_LONGITUDE -84.397348#define ZOOM_LEVEL 14
void)viewDidAppear:(BOOL)animated
 {
     [super viewDidAppear:animated];
     
     CLLocationCoordinate2D centerCoord = { GEORGIA_TECH_LATITUDE, GEORGIA_TECH_LONGITUDE };
     [mapView setCenterCoordinate:centerCoord zoomLevel:ZOOM_LEVEL animated:NO];
 }

And, viola! Your map should zoom in to where you can see the Georgia Tech campus.

Results

To verify that the zoom level is set correctly, I wrote a simple web-based Google Maps application to make sure the web and native zoom levels matched. Both apps were centered at {33.777328, -84.397348} (Georgia Tech). In the images below, the iPhone on the left is running the native app and the iPhone on the right is running the web app:

As you can see, they match.

That’s a Wrap

MKMapView+ZoomLevel

Next time, I’ll go over exactly why the code above works. But, for now, enjoy the freedom to set zoom levels!

Posted in iPhone DevelopmentTagged mapkit, maps

60 Responses to “Set the Zoom Level of an MKMapView”

1. RAVI KB 
     November 22, 2013 at 6:36 am  
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 Great job
 But from this how do I will get current zoom level of map view???2.   
    
John Gazzini 
     December 19, 2013 at 4:01 am  
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 Thanks; this saved me several minutes of my life. Like… at least 4 minutes. It looks like you posted this a few years ago, but wherever you are, I hope you’re wildly successful.
 // John3. Nordin B 
     March 13, 2014 at 1:49 pm  
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 Thanks a lot for this post my friend,
 I just started developing for iOS and I was surprised why there was no way set a zoomlevel. When a user zooms, it’s because the user wants to know the exact spot of the location and not the area.
 By the way, you’re post was very easy to follow (you should be a teacher some day).4. Kyle R 
     March 13, 2014 at 4:39 pm  
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     Permalink 
     
    
 I too want to get the zoom level of a map.5. kups 
     May 10, 2014 at 6:01 am  
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 Thanks for the great tutorial. But When i used this class with 100′s of map points in same lat longs, the map points are over lapping each other and unable to click particular map point Please check this link i want to display using spiderfy leafleft animation.. SO by using spiderfy animation we can achive this http://www.yourmapper.com/demo/spiderfy.htm . any idea?6. Thai 
     May 16, 2015 at 4:50 am  
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 Your post was very helpful that can help me convert a zoom from Google map to a span on Apple map. Thanks a lot.
 Do you know how to get a zoom level if I have a span. I think I need to do the contrary but I not very good at math and those calculation are really complicated
 Thanks in advance7.   
    
Mike 
     June 9, 2015 at 3:28 am  
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 If anyone needs it I translated this to a Swit extension for use in a project I’m working on.
 I’ll be adding the inverse operation soon (need it for same project). Just working out some kinks in it now.
 Thanks Troy for this and thanks to Dave in the comments for the inverse function.
 https://github.com/goto10/EBCExtensions8. Ahmed ESS 
     June 14, 2015 at 12:07 pm  
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 For those who need to get zoom level, use that code :
 @interface MKMapView (ZoomLevelGetter)
 - (int)getZoomLevel;
 @end
 @implementation MKMapView (ZoomLevelGetter)
 - (int)getZoomLevel
 {
 CLLocationDegrees longitudeDelta = self.region.span.longitudeDelta;
 CGFloat mapWidthInPixels = self.bounds.size.width*2;//2 is for retina display
 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 (int)zoomer;
 }
 @end9. Mike Lanza 
     September 29, 2015 at 9:03 pm  
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 Thanks to Mike for the Swift Extension! I do need the inverse function, so I hope you get around to posting it.10.   
    
ヘアアクセ 
     November 27, 2015 at 6:57 am  
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     Permalink

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标签：Set,Level,double,self,缩放,zoom,zoomLevel,MERCATOR,level
From： https://blog.51cto.com/u_16124099/6326804