Distance from CLLocation

distance.m

//Uses the haversine formula.
-(double) distanceFromCLLocation:(CLLocation*)location {
    double result;
   
    double earthRadius = 3959; //miles
   
    double latDelta = (location.coordinate.latitude - self.latitude.doubleValue) * (M_PI/180);
    double lonDelta = (location.coordinate.longitude  - self.longitude.doubleValue) * (M_PI/180);
   
    double lat1 = self.latitude.doubleValue * (M_PI/180);
    double lat2 = location.coordinate.latitude * (M_PI/180);
   
    double a = (sin(latDelta/2) * sin(latDelta/2)) + (sin(lonDelta/2) * sin(lonDelta/2)) * (cos(lat1) * cos(lat2));
    double c = 2 * atan2(sqrt(a), sqrt(1-a));
   
    result = earthRadius * c;

    return result;
}