iphone - GPS coordinates in degrees to calculate distances

Question

On the iPhone, I get the user's location in decimal degrees, for example: latitude 39.470920 and longitude = -0.373192; That's point A.

I need to create a line with another GPS coordinate, also in decimal degrees, point B. Then, calculate the distance (perpendicular) between the line from A to B and another point C.

The problem is I get confused with the values in degrees. I would like to have the result in meters. What's the conversion needed? How will the final formula to compute this look like?

Answer 1

Why don't you use CLLocations distanceFromLocation: method? It will tell you the precise distance between the receiver and another CLLocation.

CLLocation *locationA = [[CLLocation alloc] initWithLatitude:12.123456 longitude:12.123456];
CLLocation *locationB = [[CLLocation alloc] initWithLatitude:21.654321 longitude:21.654321];

CLLocationDistance distanceInMeters = [locationA distanceFromLocation:locationB];

// CLLocation is aka double

[locationA release];
[locationB release];

It's as easy as that.