Google Maps GMap2.getBoundsZoomLevel(bounds)的等效Objective-C代码?

我对Google Maps API很熟悉,现在我正在尝试学习iOS MapKit库。我有一个iPhone应用程序,它接受一个输入字符串,并使用Google Maps geocoder服务对其进行地理编码。我还想为新地图设置一个适当的缩放级别,但我不太确定如何做。

Determining zoom level from single LatLong in Google Maps API

我的计划是解析来自Google Maps API的JSON响应并提取ExtendedData字段。

 "ExtendedData":{
     "LatLonBox":{
         "north":34.13919,
         "south":34.067018, 
         "east":-118.38971, 
         "west":-118.442796
     }

然后我想使用MapKit setRegion函数相应地设置我的映射的边界。

我开始设计一个函数来做这个,但是我对逻辑有点迷茫。。。

- (void) setMapZoomForLocation(CLLocationCoordinate2D location, double north, double south, double east, double west){

    // some fancy math here....

    // set map region
    MKCoordinateRegion region;
    region.center = location;
    MKCoordinateSpan span;

    // set the span so that the map bounds are correct
    span.latitudeDelta = ???;
    span.longitudeDelta = ???;

    region.span = span;
    [self.mapView setRegion:region animated:YES];
}

或者,我想我可以使用地理代码结果的精度来设置一种默认的缩放级别。我只是不知道如何计算不同结果的等效默认缩放级别。

见 https://code.google.com/apis/maps/documentation/geocoding/v2/#GeocodingAccuracy

// parse json result
NSDictionary *results = [jsonString JSONValue];
NSArray *placemarks = (NSArray *) [results objectForKey:@"Placemark"];
NSDictionary *firstPlacemark = [placemarks objectAtIndex:0];

// parse out location
NSDictionary *point = (NSDictionary *) [firstPlacemark objectForKey:@"Point"];
NSArray *coordinates = (NSArray *) [point objectForKey:@"coordinates"];
CLLocationCoordinate2D location;
location.latitude = [[coordinates objectAtIndex:1] doubleValue];
location.longitude = [[coordinates objectAtIndex:0] doubleValue];
// DEBUG
//NSLog(@"Parsed Location: (%g,%g)", location.latitude, location.longitude);

// parse out suggested bounding box
NSDictionary *extendedData = (NSDictionary *) [firstPlacemark objectForKey:@"ExtendedData"];
NSDictionary *latLngBox = (NSDictionary *) [extendedData objectForKey:@"LatLonBox"];

double north = [[latLngBox objectForKey:@"north"] doubleValue];
double south = [[latLngBox objectForKey:@"south"] doubleValue];
double east = [[latLngBox objectForKey:@"east"] doubleValue];
double west = [[latLngBox objectForKey:@"west"] doubleValue];
// DEBUG
//NSLog(@"Parsed Bounding Box: ne = (%g,%g), sw = (%g,%g)", north, east, south, west);

MKCoordinateSpan span = MKCoordinateSpanMake(fabs(north - south), fabs(east - west));
MKCoordinateRegion region = MKCoordinateRegionMake(location, span);
[self.mapView setRegion:region animated:YES];