高德地图缩放

#import <MAMapKit/MAMapKit.h>

@interface MAMapView (ZoomLevel)
- (NSUInteger)getZoomLevel;

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

- (void)zoomToFitMapAnnotations;
@end

//
//  MAMapView+ZoomLevel.m
//  Yjf
//
//  Created by iMac on 14/12/2.
//  Copyright (c) 2014年 POTech. All rights reserved.
//

#import "MAMapView+ZoomLevel.h"

#define MERCATOR_OFFSET 268435456
#define MERCATOR_RADIUS 85445659.44705395

@implementation MAMapView (ZoomLevel)

#pragma mark - Map conversion methods

- (double)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 - Helper methods

- (MACoordinateSpan)coordinateSpanWithMapView:(MAMapView *)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
    MACoordinateSpan span = MACoordinateSpanMake(latitudeDelta, longitudeDelta);
    return span;
}

#pragma mark - Public methods

- (NSUInteger)getZoomLevel
{
    return 21-round(log2(self.region.span.longitudeDelta * MERCATOR_RADIUS * M_PI / (180.0 * self.bounds.size.width)));
}

- (void)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
    MACoordinateSpan span = [self coordinateSpanWithMapView:self centerCoordinate:centerCoordinate andZoomLevel:zoomLevel];
    MACoordinateRegion region = MACoordinateRegionMake(centerCoordinate, span);
    
    // set the region like normal
    [self setRegion:region animated:animated];
}

- (void)zoomToFitMapAnnotations
{
    if ([self.annotations count] == 0) return;
    
    CLLocationCoordinate2D topLeftCoord;
    topLeftCoord.latitude = -90;
    topLeftCoord.longitude = 180;
    
    CLLocationCoordinate2D bottomRightCoord;
    bottomRightCoord.latitude = 90;
    bottomRightCoord.longitude = -180;
    
    for(id<MAAnnotation> annotation in self.annotations) {
        if ([annotation isKindOfClass:[MAUserLocation class]]) {
            continue;
        }
        topLeftCoord.longitude = fmin(topLeftCoord.longitude, annotation.coordinate.longitude);
        topLeftCoord.latitude = fmax(topLeftCoord.latitude, annotation.coordinate.latitude);
        bottomRightCoord.longitude = fmax(bottomRightCoord.longitude, annotation.coordinate.longitude);
        bottomRightCoord.latitude = fmin(bottomRightCoord.latitude, annotation.coordinate.latitude);
    }
    
    MACoordinateRegion region;
    region.center.latitude = topLeftCoord.latitude - (topLeftCoord.latitude - bottomRightCoord.latitude) * 0.5;
    region.center.longitude = topLeftCoord.longitude + (bottomRightCoord.longitude - topLeftCoord.longitude) * 0.5;
    region.span.latitudeDelta = fabs(topLeftCoord.latitude - bottomRightCoord.latitude) * 1.2;
    region.span.longitudeDelta = fabs(bottomRightCoord.longitude - topLeftCoord.longitude) * 1.2;
    
    region = [self regionThatFits:region];
    [self setRegion:region animated:YES];
}

@end