Displaying current location on Google maps

Question

I have an iOS app that uses Google Maps SDK to display a map within my app.

I have managed to get the map displaying but I dont know how to set the camera or the marker to the users current location.

I have hard coded the coordinates just to test is the map working but I am now stuck on how to display current location of the user.

Here is my code to centre the camera to a coordinate

- (void)viewDidLoad
{
    [super viewDidLoad];

    GMSCameraPosition *camera = [GMSCameraPosition cameraWithLatitude:47.995602 longitude:-78.902153 zoom:6];

    self.mapView = [GMSMapView mapWithFrame:CGRectZero camera:camera];

    self.mapView.myLocationEnabled = YES;
    self.mapView.mapType = kGMSTypeNormal;
    self.mapView.accessibilityElementsHidden = NO;
    self.mapView.settings.scrollGestures = YES;
    self.mapView.settings.zoomGestures = YES;
    self.mapView.settings.compassButton = YES;
    self.mapView.settings.myLocationButton = YES;
    self.mapView.delegate = self;
    self.view = self.mapView;

    [self placeMarkers];
}

And here is the code to display the marker at coordinates

-(void)placeMarkers
{
    GMSMarker *marker = [[GMSMarker alloc] init];

    marker.position = CLLocationCoordinate2DMake(47.995602, -78.902153);
    marker.title = @"PopUp HQ";
    marker.snippet = @"Durham, NC";
    marker.icon = [GMSMarker markerImageWithColor:[UIColor blueColor]];
    marker.opacity = 0.9;
    marker.map = self.mapView;
}

I have tried to get the current position as follows:

CLLocationCoordinate2D *myLocation = self.mapView.myLocation.coordinate;

but I get the error:

Initializing 'CLLocationCoordinate2D' with an expression of incompatible type 'CLLocationCoordinate2D'

How can I get the current location to pass to the camera as well as marker?

NigelG · Accepted Answer · 2014-05-23T09:06:32.003

CLLocationCoordinate2D is just a struct containing a latitude and longitude, so you can simply use

CLLocationCoordinate2D myLocation = self.mapView.myLocation.coordinate;

It is also worth using KVO to observe changes to myLocation, as it is possible that the mapView won't yet have a valid location.

To explain further about KVO:

You can add an observer for the myLocation property as follows:

[self.mapView addObserver:self
          forKeyPath:@"myLocation"
             options:(NSKeyValueObservingOptionNew |
                      NSKeyValueObservingOptionOld)
             context:NULL];

You should then implement the following method:

- (void)observeValueForKeyPath:(NSString *)keyPath
                  ofObject:(id)object
                    change:(NSDictionary *)change
                   context:(void *)context {
    if ([keyPath isEqualToString:@"myLocation"]) {
//            NSLog(@"My position changed");
    }
}

You can then safely access self.mapView.myLocation.coordinate knowing that the location is valid.

Don't forget to remove yourself as an observer when the mapview is deallocated:

[self.mapView removeObserver:self forKeyPath:@"myLocation"];

As Saxon has already mentioned, the mapview will show it's own current position indicator. The marker that you are adding will be shown in addition, but it is likely that mapview doesn't yet having a valid position when you are creating the marker, so it is being added at latitude/longitude 0,0 which is in the middle of the ocean.

OK that seems to be moving the marker from its hard coded position. But its now placing the marker in the middle of the ocean - just of the west coast of Africa (where I am not). If I zoom out I can see another marker on the screen with my correct location but I have no idea where this is coming from? I have set both the camera and marker to myLocation.latitude and myLocation.longitude and the app seems to think this is in the middle of the ocean? Is there something else I need to check and where does the other marker come from? — heyred, May 22 '14 at 20:40

score 1 · Answer 2 · answered May 23 '14 at 00:00

When you set myLocationEnabled to YES then the map automatically adds a marker at your current location. So you probably don't need to add your own?

It takes time for the device and your app to determine your location. When it starts up it probably doesn't know your location yet, so it defaults to lat/lon of zero, which is off Africa.

As NigelG said, you can use KVO on the myLocation property to find out when the position updates.

Displaying current location on Google maps

2 Answers2