code: function(ms) {
      var axes = this._cam.mainAxes();
      var intervals = [ new utils.Range(), new utils.Range(), new utils.Range() ];
      this.forEach(function(obj) {
        if (!obj.visible()) {
          return;
        }
        obj.updateProjectionIntervals(axes[0], axes[1], axes[2], intervals[0],
                                      intervals[1], intervals[2]);
      });
      this._fitToIntervals(axes, intervals, ms);
    }
docs: adapt the zoom level to fit the viewport to all visible objects.