How to determine if an annotation is inside of MKPolygonView (iOS)

Question

I'm trying to calculate if a specific annotation(like the blue circle of the user location) or a MKPinAnnotation is inside an MKPolygon layer on the mapview.

Any advice to achieve this?

Priscilapriscilla

Answer 1

The following converts the coordinate to a CGPoint in the polygon view and uses CGPathContainsPoint to test if that point is in the path (which may be non-rectangular):

CLLocationCoordinate2D mapCoordinate = ...; //user location or annot coord

MKMapPoint mapPoint = MKMapPointForCoordinate(mapCoordinate);

MKPolygonView *polygonView = 
    (MKPolygonView *)[mapView viewForOverlay:polygonOverlay];

CGPoint polygonViewPoint = [polygonView pointForMapPoint:mapPoint];

BOOL mapCoordinateIsInPolygon = 
    CGPathContainsPoint(polygonView.path, NULL, polygonViewPoint, NO);

This should work with any overlay view that is a subclass of MKOverlayPathView. You can actually replace MKPolygonView with MKOverlayPathView in the example.

Chara

Would this work on MKPolygons with holes (internal polygons)? – Autry

@Greg Combs: If the polygon (or overlay path) has holes, CGPathContainsPoint will return NO if the point queried is in a hole. – Chara

@AnnaKarenina - how to determine this same mapCoordinateIsInPolygon value for a scenario with MKPolygon but no map view? (because all I have is set of coordinates but no need for a view) – Sclera

How could this be achieved for a MKPolygon in memory, but not on a map? – Tarr

@capikaw: By creating a CGMutablePathRef as described in comment to NiravBhatt above. An MKPolygon or map is not needed since the key part is CGPathContainsPoint. Create a CGMutablePathRef from the coordinates (use longitude for x value and latitude for the y value). – Chara

In the current release of iOS 7, the path property seems to incorrectly return NULL making the above approach fail. For a workaround, see #19015426. – Chara

Is there any solution in IOS7 for this issue? – Sophisticate

@UserDev, see the comment above starting with "In the current release of iOS 7...". It gives a link to a workaround. – Chara

[MKPolygonView initWithPolygon] is deprecated in iOS 7 but can be replaced with MKPolygonRenderer. – Pasteurism

Answer 2

Slightly modified above to do calculations for points/coordinates in polygons without the use of a MKMapView formatted as an extension to MKPolygon class:

//MKPolygon+PointInPolygon.h

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface MKPolygon (PointInPolygon)

-(BOOL)coordInPolygon:(CLLocationCoordinate2D)coord;
-(BOOL)pointInPolygon:(MKMapPoint)point;

@end

---

//MKPolygon+PointInPolygon.m

#import "MKPolygon+PointInPolygon.h"

@implementation MKPolygon (PointInPolygon)

-(BOOL)coordInPolygon:(CLLocationCoordinate2D)coord {

    MKMapPoint mapPoint = MKMapPointForCoordinate(coord);
    return [self pointInPolygon:mapPoint];
}

-(BOOL)pointInPolygon:(MKMapPoint)mapPoint {

    MKPolygonRenderer *polygonRenderer = [[MKPolygonRenderer alloc] initWithPolygon:self];
    CGPoint polygonViewPoint = [polygonRenderer pointForMapPoint:mapPoint];
    return CGPathContainsPoint(polygonRenderer.path, NULL, polygonViewPoint, NO);
}

@end

Enjoy!

Tarr

[MKPolygonView initWithPolygon] is deprecated in iOS 7 but can be replaced it with MKPolygonRenderer. – Pasteurism