Geo-Fencing using Google Map in iPhone - ios

Question

I am trying to Geo-fence using Google Map for iPhone app.
A lot of tutorials can be found for MKMapView. But can't find for the GMSMapView.
The basic thing is how to convert the screen coordinate (x,y) to the MapCoordinate lat/lng.
Is there any API available for Google Map in iOS for that conversion?
Thanks

Answer 1

You can use something like this:
GMSMapView* mapView = ...;
CGPoint point = ...;
...
CLLocationCoordinate2D coordinate =
[mapView.projection coordinateForPoint: point];
UPDATE:
The comments on the projection property in GMSMapView.h are:
/**
* The GMSProjection currently used by this GMSMapView. This is a snapshot of
* the current projection, and will not automatically update when the camera
* moves. The projection may be nil while the render is not running (if the map
* is not yet part of your UI, or is part of a hidden UIViewController, or you
* have called stopRendering).
*/
#property (nonatomic, readonly) GMSProjection *projection;
Therefore you can only access the .projection property after the map has rendered. It will be nil if you try to access it during loadView or viewDidLoad.
I don't know if there is a better way to tell if the map has been rendered, but I noticed that the mapView:didChangeCameraPosition: method is called once after the map view is first displayed, and that the map's projection property is valid there.
So, in your view controller's header, add GMSMapViewDelegate:
#interface ViewController : UIViewController <GMSMapViewDelegate>
When you allocate the map view, assign the delegate:
_map = [GMSMapView mapWithFrame: CGRectMake(0, 0, width, height) camera: camera];
_map.delegate = self;
[self.view addSubview: _map];
Then add the delegate method:
- (void)mapView: (GMSMapView*)mapView
didChangeCameraPosition: (GMSCameraPosition*)position
{
CGPoint point = CGPointMake(x, y);
CLLocationCoordinate2D coordinate =
[_map.projection coordinateForPoint: point];
}
Note that mapView:didChangeCameraPosition: is called every time the user changes the camera, so you'd probably need to use a flag, so that you only do your calculations the first time mapView:didChangeCameraPosition: is called.

Answer 2

No need to convert x,y to lat,long.
GMSCircle *fence = [GMSCircle circleWithPosition:locationCord radius:fenceRadius];
[fence setFillColor:[UIColor colorWithRed:102.0/255 green:178.0/255 blue:255.0/255 alpha:0.3]];
[fence setZIndex:100];
[fence setMap: _map];
Add this code when you are making GMSMapView and geo fence will be shown with your location marker.