Why does MKMetersBetweenMapPoints give me different results when I swap the parameters? - iphone

Question

I'm actually trying to calculate the distance between the max and min point in the x and y coordinates for the MKMapPoints.
For that, I'm doing this (max distance in y axis):
MKMapPoint test1, test2;
double dist;
test1.x = 0.0;
test1.y = 0.0;
test2.x = 0.0;
test2.y = MKMapSizeWorld.height;
dist = MKMetersBetweenMapPoints(test2, test1);
NSLog(#"Distance %f",dist);
I get 18997878.291251 in the console. But when I change the distance calculation to:
dist = MKMetersBetweenMapPoints(test1, test2);
I get 18873651.664238, so I don't understand what's the difference. I don't even know if I'm doing the right thing to get the max values of distance in the x and y axes.
Any help will be appreciated.

Answer 1

I guess it's an algorithm problem. Some kind of approximation that stops when a certain precision is achieved. That's why no commutation there. You can try sample code to get distance between two points on map without using MKMapPoints:
- (float) distanceToLPU {
useDelegate
CLLocationCoordinate2D pointACoordinate = appDelegate.usrLoc;
CLLocation *pointALocation = [[CLLocation alloc] initWithLatitude:pointACoordinate.latitude longitude:pointACoordinate.longitude];
CLLocationCoordinate2D pointBCoordinate;
pointBCoordinate.latitude = [self.latitude doubleValue];
pointBCoordinate.longitude = [self.longitude doubleValue];
CLLocation *pointBLocation = [[CLLocation alloc] initWithLatitude:pointBCoordinate.latitude longitude:pointBCoordinate.longitude];
float distanceMeters = [pointALocation distanceFromLocation:pointBLocation];
[pointALocation release];
[pointBLocation release];
NSString *dist = [NSString stringWithFormat:#" (%.0f м)", distanceMeters];
NSLog(#"Distance to this LPU:%#", dist);
return distanceMeters;
}