iOS MapKit Annotation, not showing correct location

Question

I using a custom image for my mapkit annotation. But the main problem it seems that I am running into in using a custom image, is that when zoomed out, the annotation is not in the correct point on the map, and ONLY until I zoom in all the way down, will it show the annotation point in the correct place. It seems that when I use a regular pin MKPinAnnotationView, it works normally, as with the pin being in the correct place zoomed in or out, thanks in advance for anyone that can help.

The code I have used is as follows:

- (MKAnnotationView *)mapView:(MKMapView *)aMapView viewForAnnotation:(id <MKAnnotation>)annotation
{

NSLog(@"welcome into the map view annotation");

if ([annotation isKindOfClass:[MKUserLocation class]])

return nil;

MKAnnotationView *pprMapNote = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"pprMapNote"];


pprMapNote.image = [UIImage imageNamed:[NSString stringWithFormat:@"GPS_note.png"]];

pprMapNote.canShowCallout = YES;
pprMapNote.centerOffset = CGPointMake(-21,-60);
pprMapNote.calloutOffset = CGPointMake(0, 0);
//[pprMapNote addSubview:pprMapNoteImg];

UIButton* rightButton = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
[rightButton addTarget:self
                action:@selector(showDetail)
      forControlEvents:UIControlEventTouchUpInside];
pprMapNote.rightCalloutAccessoryView = rightButton;

//remember to write in conditional for the different icons that should be loaded based on location

UIImageView *pprNoteLocIcon = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"loc_icon_casino.png"]];
pprMapNote.leftCalloutAccessoryView = pprNoteLocIcon;
[pprNoteLocIcon release];

return pprMapNote;

}

Answer 1

You are setting the centerOffset of the annotation view.

Note that this offset is not scaled with the zoom level. The further you zoom out, the further the image will appear from the coordinate.

In the default MKPinAnnotationView, the centerOffset is left at the default of 0,0 and the pin image is designed such that the bottom point of the pin is on the coordinate. So as you zoom further out, the pin image seems to grow relative to the map under it but the bottom of the pin is still pointing to the coordinate.

You need to either adjust the centerOffset based on your image or modify your image so you don't need to set centerOffset. Or just try commenting out the setting of centerOffset--maybe you don't need it.

Some other unrelated items:

• You have a memory leak for the pprMapNote alloc+init (add an autorelease)
• You should be using dequeueReusableAnnotationViewWithIdentifier to allow for annotation view re-use.
• Instead of using addTarget to call your own method for the callout button press, it's much better to use the map view's own delegate method calloutAccessoryControlTapped

See this answer for an example of the above three points.

Answer 2

The Pin is drawn in a separate view, so it will not zoom based on the status of your view.

You have to set the size of your custom Pin image manually. This can easily be done using the centerOffset. For most cases it is enough to set the height of the frame to half the size of the image. The image is fully filled in the frame, so you can easily use this frame size(height).

  aView.image = [UIImage imageNamed ... ];
  aView.centerOffset = CGPointMake(0,-aView.frame.size.height*0.5);