internal Point GetMiddlePoint(bool invertRotation)
{
var middlePt = new Point(ActualWidth / 2, ActualHeight / 2);
Point rotatedPt = rotate90.Transform(middlePt);
if (invertRotation && _invertTransform != null)
rotatedPt = new Point(2 * middlePt.X - rotatedPt.X, 2 * middlePt.Y - rotatedPt.Y);
return rotatedPt;
}