I'm guessing you try to calculate the degrees between the coordinates of two points of interest (POI).
Calculating the arc of a great circle:
+(float) greatCircleFrom:(CLLocation*)first
to:(CLLocation*)second {
int radius = 6371; // 6371km is the radius of the earth
float dLat = second.coordinate.latitude-first.coordinate.latitude;
float dLon = second.coordinate.longitude-first.coordinate.longitude;
float a = pow(sin(dLat/2),2) + cos(first.coordinate.latitude)*cos(second.coordinate.latitude) * pow(sin(dLon/2),2);
float c = 2 * atan2(sqrt(a),sqrt(1-a));
float d = radius * c;
return d;
}
Another option is to pretend you are on cartesian coordinates (faster but not without error on long distances):
+(float)angleFromCoordinate:(CLLocationCoordinate2D)first
toCoordinate:(CLLocationCoordinate2D)second {
float deltaLongitude = second.longitude - first.longitude;
float deltaLatitude = second.latitude - first.latitude;
float angle = (M_PI * .5f) - atan(deltaLatitude / deltaLongitude);
if (deltaLongitude > 0) return angle;
else if (deltaLongitude < 0) return angle + M_PI;
else if (deltaLatitude < 0) return M_PI;
return 0.0f;
}
If you want the result in degrees instead radians, you have to apply the following conversion:
#define RADIANS_TO_DEGREES(radians) ((radians) * 180.0 / M_PI)
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