code: function(evt, pinchData) {
          var xy = (this.preserveCenter) ?
              this.map.getPixelFromLonLat(this.map.getCenter()) : evt.xy;
          this.pinchOrigin = xy;
          this.currentCenter = xy;
      }
docs: Method: pinchStart
  
  Parameters:
  evt - {Event}
  pinchData - {Object} pinch data object related to the current touchmove
  of the pinch gesture. This give us the current scale of the pinch.