Mike D Mike D - 1 month ago 14
Objective-C Question

Determining Midpoint Between 2 Cooridinates

I am trying to determine the midpoint between to locations in an

MKMapView
. I am following the method outlined here (and here) and rewrote it in Objective-C, but the map is being centered somewhere northeast of Baffin Island, which is no where near the two points.

My method based on the java method linked above:

+(CLLocationCoordinate2D)findCenterPoint:(CLLocationCoordinate2D)_lo1 :(CLLocationCoordinate2D)_loc2 {
CLLocationCoordinate2D center;

double lon1 = _lo1.longitude * M_PI / 180;
double lon2 = _loc2.longitude * M_PI / 100;

double lat1 = _lo1.latitude * M_PI / 180;
double lat2 = _loc2.latitude * M_PI / 100;

double dLon = lon2 - lon1;

double x = cos(lat2) * cos(dLon);
double y = cos(lat2) * sin(dLon);

double lat3 = atan2( sin(lat1) + sin(lat2), sqrt((cos(lat1) + x) * (cos(lat1) + x) + y * y) );
double lon3 = lon1 + atan2(y, cos(lat1) + x);

center.latitude = lat3 * 180 / M_PI;
center.longitude = lon3 * 180 / M_PI;

return center;
}


The 2 parameters have the following data:

_loc1:
latitude = 45.4959839
longitude = -73.67826455

_loc2:
latitude = 45.482889
longitude = -73.57522299


The above are correctly place on the map (in and around Montreal). I am trying to center the map in the midpoint between the 2, yet my method return the following:

latitude = 65.29055
longitude = -82.55425


which somewhere in the arctic, when it should be around 500 miles south.

Answer

Just a hunch, but I noticed your lon2 and lat2 variables are being computed with M_PI/100 and not M_PI/180.

double lon1 = _lo1.longitude * M_PI / 180;
double lon2 = _loc2.longitude * M_PI / 100;

double lat1 = _lo1.latitude * M_PI / 180;
double lat2 = _loc2.latitude * M_PI / 100;

Changing those to 180 might help you out a bit.