code: function ProjectionHelperOverlay(map) {
  
    this.setMap(map);
  
    var TILEFACTOR = 8;
    var TILESIDE = 1 << TILEFACTOR;
    var RADIUS = 7;
  
    this._map = map;
    this._zoom = -1;
    this._X0 =
    this._Y0 =
    this._X1 =
    this._Y1 = -1;
  
  
  }
docs: Projection overlay helper. Helps in calculating
  that markers get into the right grid.
  @constructor
  @param {Map} map The map to manage.