[Code Snippet] Geolocating photos with reverse geocoding.

Sometimes you have an app which takes a photo, and you want to geolocate it obtaining current latitude, longitude and altitude from the GPS, but generally for the user this info is not useful, it has not a Reverse Geocoder in its brain so the user should prefer to see a name than three numbers.

In this code snippet we're going to se how to accomplish this.

First thing to do is to add the required frameworks to our app.

CoreLocation Framework

MapKit Framework

Next, in your .h file you have to import these frameworks and implement the protocols that we need.

#import <corelocation corelocation.h>
#import <mapkit mapkit.h>

@interface geolocatingPhotoViewController : UIViewController <UIImagePickerControllerDelegate,  CLLocationManagerDelegate, MKReverseGeocoderDelegate>

Let's take the photo with UIImagePickerController and when we've token it, we call CLLocationManager to get our position.

UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init]; imagePicker.delegate = self;
imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
[self presentModalViewController:imagePicker animated:YES];
[imagePicker release]; 

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo {

self.imageViewCaptura.image = image;
[picker dismissModalViewControllerAnimated:YES];
CLLocationManager * locationManager = [[CLLocationManager alloc] init]; locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters; [locationManager startUpdatingLocation];

}

Once we have our image stored in a UIImageView and we have to wait the CLLocationManager to get our position coordinates. When we have it, we stop the location and call the reverse geocoding to start getting the location name.

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {

[locationManager stopUpdatingLocation];
[locationManager release];
capture.longitude = newLocation.coordinate.longitude;
capture.latitude = newLocation.coordinate.latitude;
capture.altitude = newLocation.altitude;

CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(capture.latitude, capture.longitude);
MKReverseGeoCoder *reverserGeoCoder = [[MKReverseGeocoder alloc] initWithCoordinate:coordinate];
reverserGeoCoder.delegate = self; 
[reverserGeoCoder start];

}

At last, if MKReverseGeoCoder was able to get the coordinates info, we only has to get the data and show it.

- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFindPlacemark:(MKPlacemark *)placemark {

if (placemark)
{

NSString *strLocation = [NSString stringWithFormat:@"%@, %@ (%@)", placemark.locality, placemark.administrativeArea, placemark.country]; self.textFieldLocation.text = strLocation;

}
NSLog(@"Location info: %@", strLocation );

}

We should control if GKReverseGeocoder wasn't able to retrieve our position information implementing didFailWithError function.

And that's all, now you know how to present location info to the user when it takes a photo.

Enjoy it!