private void OnPinchStarted(object sender, PinchStartedGestureEventArgs e)
        {
            initialAngle = PanTransform.Rotation;
            initialScale = PanTransform.ScaleX;

            UpdateDebugData();
        }

        private void OnPinchDelta(object sender, PinchGestureEventArgs e)
        {
            //Rotation
            //PanTransform.Rotation = initialAngle + e.TotalAngleDelta;

            double maxVal = 3;
            double minVal = 1;

            //calculate data
            double deltaVal = initialScale * e.DistanceRatio;

            if (deltaVal >= minVal && deltaVal < maxVal)
            {
                PanTransform.ScaleX = deltaVal;
                PanTransform.ScaleY = deltaVal;
            }
            else
            {
                if ((deltaVal - minVal) < (maxVal - deltaVal))
                {
                    //näher bei minVal
                    PanTransform.ScaleX = minVal;
                    PanTransform.ScaleY = minVal;
                }
                else
                {
                    //näher bei maxVal
                    PanTransform.ScaleX = maxVal;
                    PanTransform.ScaleY = maxVal;
                }
            }

            UpdateDebugData();
        }

        private void GestureListener_DragDelta(object sender, DragDeltaGestureEventArgs e)
        {
            PanTransform.TranslateX += e.HorizontalChange;
            PanTransform.TranslateY += e.VerticalChange;

            UpdateDebugData();
        }