function keydown( event ) {

		if ( ! _this.enabled ) return;

		//event.preventDefault();

		if ( _state !== STATE.NONE ) {

			return;

		} else if ( event.keyCode === _this.keys[ STATE.ROTATE ] && !_this.noRotate ) {

			_state = STATE.ROTATE;

		} else if ( event.keyCode === _this.keys[ STATE.ZOOM ] && !_this.noZoom ) {

			_state = STATE.ZOOM;

		} else if ( event.keyCode === _this.keys[ STATE.PAN ] && !_this.noPan ) {

			_state = STATE.PAN;

		}

		if ( _state !== STATE.NONE ) {

			_keyPressed = true;

		}

	}
@author Eberhard Graether / http://egraether.com/