Calculate the center/average of multiple GeoLocation coordinates

average-geolocation.js

/**
 * Calculate the center/average of multiple GeoLocation coordinates
 * Expects an array of objects with .latitude and .longitude properties
 *
 * @url http://stackoverflow.com/a/14231286/538646
 */
function averageGeolocation(coords) {
  if (coords.length === 1) {
    return coords[0];
  }

  let x = 0.0;
  let y = 0.0;
  let z = 0.0;

  for (let coord of coords) {
    let latitude = coord.latitude * Math.PI / 180;
    let longitude = coord.longitude * Math.PI / 180;

    x += Math.cos(latitude) * Math.cos(longitude);
    y += Math.cos(latitude) * Math.sin(longitude);
    z += Math.sin(latitude);
  }

  let total = coords.length;

  x = x / total;
  y = y / total;
  z = z / total;

  let centralLongitude = Math.atan2(y, x);
  let centralSquareRoot = Math.sqrt(x * x + y * y);
  let centralLatitude = Math.atan2(z, centralSquareRoot);

  return {
    latitude: centralLatitude * 180 / Math.PI,
    longitude: centralLongitude * 180 / Math.PI
  };
}

// expect ~ 37.790831, -122.407169
const sf = [{
  latitude: 37.797749,
  longitude: -122.412147
}, {
  latitude: 37.789068,
  longitude: -122.390604
}, {
  latitude: 37.785269,
  longitude: -122.421975
}];

console.log(averageGeolocation(sf));

// expect ~ 8.670552, -173.207864
const globe = [{ // Japan
  latitude: 37.928969,
  longitude: 138.979637
}, { // Nevada
  latitude: 39.029788,
  longitude: -119.594585
}, { // New Zealand
  latitude: -39.298237,
  longitude: 175.717917
}];

console.log(averageGeolocation(globe));