objective c - How to make the union between two MKCoordinateRegion

Question

I'm trying to do the union between two MKCoordinateRegion. Does anybody have an idea on how to do this?

Answer 1

There is a MKMapRectUnion function which accepts two MKMapRects so you could first convert each MKCoordinateRegion to an MKMapRect and then call that function (and convert the result back to an MKCoordinateRegion using the MKCoordinateRegionForMapRect function).

The conversion method might look like this:

- (MKMapRect)mapRectForCoordinateRegion:(MKCoordinateRegion)coordinateRegion
{
    CLLocationCoordinate2D topLeftCoordinate = 
        CLLocationCoordinate2DMake(coordinateRegion.center.latitude 
                + (coordinateRegion.span.latitudeDelta/2.0), 
            coordinateRegion.center.longitude 
                - (coordinateRegion.span.longitudeDelta/2.0));

    MKMapPoint topLeftMapPoint = MKMapPointForCoordinate(topLeftCoordinate);

    CLLocationCoordinate2D bottomRightCoordinate = 
        CLLocationCoordinate2DMake(coordinateRegion.center.latitude 
                - (coordinateRegion.span.latitudeDelta/2.0), 
            coordinateRegion.center.longitude 
                + (coordinateRegion.span.longitudeDelta/2.0));

    MKMapPoint bottomRightMapPoint = MKMapPointForCoordinate(bottomRightCoordinate);

    MKMapRect mapRect = MKMapRectMake(topLeftMapPoint.x, 
                            topLeftMapPoint.y, 
                            fabs(bottomRightMapPoint.x-topLeftMapPoint.x), 
                            fabs(bottomRightMapPoint.y-topLeftMapPoint.y));

    return mapRect;
}

Then, to actually do the union:

MKCoordinateRegion region1 = ...
MKCoordinateRegion region2 = ...

MKMapRect mapRect1 = [self mapRectForCoordinateRegion:region1];
MKMapRect mapRect2 = [self mapRectForCoordinateRegion:region2];

MKMapRect mapRectUnion = MKMapRectUnion(mapRect1, mapRect2);

MKCoordinateRegion regionUnion = MKCoordinateRegionForMapRect(mapRectUnion);