Map Bounding Box with Annotations

Question

I have an algorithm that calculates the size and location of a bounding box for a map that contains a set of given coordinates. While it works perfectly, the bounds that it produces don't always accommodate the push pin that I place at coordinates that often lie right on the edge of the bounding box:

...and again, it produces an acceptable result most of the time:

I've mulled it over for awhile, but I haven't been able to think of a way to modify my algorithm to ensure that the push pins are always within the bounding box. My algorithm is listed below, and any suggestions would be greatly appreciated. :)

MKMapPoint *points = malloc([coordinates count] * sizeof(MKMapPoint));    
MKMapPoint upperRightCorner;
MKMapPoint lowerLeftCorner;

for(int i = 0; i < [coordinates count]; i++) 
{
    CLLocation *location = [coordinates objectAtIndex:i];
    CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(herp.coordinate.latitude, herp.coordinate.longitude);

    MKMapPoint point = MKMapPointForCoordinate(coordinate);
    points[i] = point;

    if (i == 0) {
        upperRightCorner = point;
        lowerLeftCorner = point;
    }
    else {
        if (point.x > upperRightCorner.x) upperRightCorner.x = point.x;
        if (point.y > upperRightCorner.y) upperRightCorner.y = point.y;
        if (point.x < lowerLeftCorner.x) lowerLeftCorner.x = point.x;
        if (point.y < lowerLeftCorner.y) lowerLeftCorner.y = point.y;
    }    
}

MKMapRect boundingBox = MKMapRectMake(lowerLeftCorner.x, lowerLeftCorner.y,
                                 upperRightCorner.x - lowerLeftCorner.x,
                                 upperRightCorner.y - lowerLeftCorner.y);

Answer 1

I think it might be late, but here's a solution it works for me, quite similar to yours, I ended up adding a padding at the end.

- (MKCoordinateRegion)boundingBoxForAnnotations:(NSArray *)annotations { 

CLLocationCoordinate2D topLeftCoord; 
topLeftCoord.latitude = -90; 
topLeftCoord.longitude = 180; 

CLLocationCoordinate2D bottomRightCoord; 
bottomRightCoord.latitude = 90; 
bottomRightCoord.longitude = -180; 

for (id<MKAnnotation> annotation in annotations) {

    topLeftCoord.longitude = fmin(topLeftCoord.longitude, annotation.coordinate.longitude); 
    topLeftCoord.latitude = fmax(topLeftCoord.latitude, annotation.coordinate.latitude); 
    bottomRightCoord.longitude = fmax(bottomRightCoord.longitude, annotation.coordinate.longitude); 
    bottomRightCoord.latitude = fmin(bottomRightCoord.latitude, annotation.coordinate.latitude); 
}

MKCoordinateRegion region; 
region.center.latitude = topLeftCoord.latitude - (topLeftCoord.latitude - bottomRightCoord.latitude) * 0.5; 
region.center.longitude = topLeftCoord.longitude + (bottomRightCoord.longitude - topLeftCoord.longitude) * 0.5; 
region.span.latitudeDelta = fabs(topLeftCoord.latitude - bottomRightCoord.latitude) * 1.1; 

region.span.longitudeDelta = fabs(bottomRightCoord.longitude - topLeftCoord.longitude) * 1.1; 

return region;

}