Angular factory that calculates the best set of coordinates to center a set of coordiantes in a map

CalculateCenter.js

app.factory('calculateCenter', function($window) {
       var coordinates = [];
       return function(data) {
           var num_coords = data.length;

           var X = 0.0;
           var Y = 0.0;
           var Z = 0.0;

           for(var i = 0; i < num_coords; i++) {
               if(data[i].latitude == 0 && data[i].longitude == 0) continue;
               var lat = data[i].latitude * Math.PI / 180;
               var lon = data[i].longitude * Math.PI / 180;

               var a = Math.cos(lat) * Math.cos(lon);
               var b = Math.cos(lat) * Math.sin(lon);
               var c = Math.sin(lat);

               X += a;
               Y += b;
               Z += c;
           }

           X /= num_coords;
           Y /= num_coords;
           Z /= num_coords;

           lon = Math.atan2(Y, X);
           var hyp = Math.sqrt(X * X + Y * Y);
           lat = Math.atan2(Z, hyp);

           coordinates.push(lat * 180 / Math.PI);
           coordinates.push(lon * 180 / Math.PI);

           return coordinates;
       }
    });