zoomLevelToFitBounds.js

/**
 * Get zoom level to fit in
 *
 * @see http://stackoverflow.com/questions/6048975/google-maps-v3-how-to-calculate-the-zoom-level-for-a-given-bounds
 *
 * @param bounds
 * @param mapWidth
 * @param mapHeight
 * @returns {number}
 */
function zoomLevelToFitBounds(bounds, mapWidth, mapHeight) {
  var worldWidth = 256;
  var worldHeight = 256;
  var ZOOM_MAX = 21;

  function latRad(lat) {
    var sin = Math.sin(lat * Math.PI / 180);
    var radX2 = Math.log((1 + sin) / (1 - sin)) / 2;
    return Math.max(Math.min(radX2, Math.PI), -Math.PI) / 2;
  }

  function zoom(mapPx, worldPx, fraction) {
    return Math.floor(Math.log(mapPx / worldPx / fraction) / Math.LN2);
  }

  var ne = bounds.getNorthEast();
  var sw = bounds.getSouthWest();

  var latFraction = (latRad(ne.lat()) - latRad(sw.lat())) / Math.PI;

  var lngDiff = ne.lng() - sw.lng();
  var lngFraction = ((lngDiff < 0) ? (lngDiff + 360) : lngDiff) / 360;

  var latZoom = zoom(mapHeight, worldHeight, latFraction);
  var lngZoom = zoom(mapWidth, worldWidth, lngFraction);

  return Math.min(latZoom, lngZoom, ZOOM_MAX);
}

module.exports = zoomLevelToFitBounds;