string s = XamlWriter.Save(obj);

          StreamGeometry streamGeometry = new StreamGeometry();
          using (StreamGeometryContext streamGeometryContext = streamGeometry.Open())
          {
            streamGeometryContext.BeginFigure(new Point(10, 10), true, false);
            streamGeometryContext.LineTo(new Point(10, 20), true, true);
            streamGeometryContext.LineTo(new Point(20, 20), true, true);
            streamGeometryContext.LineTo(new Point(20, 10), true, true);
            streamGeometryContext.LineTo(new Point(10, 10), true, true);
          }

          string _xaml01 = System.Windows.Markup.XamlWriter.Save(streamGeometry);

          Transform transform1 = new ScaleTransform(3, 3);

          streamGeometry.Transform = transform1;

          string _xaml02 = System.Windows.Markup.XamlWriter.Save(streamGeometry);

<StreamGeometry xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">M10,10L10,20 20,20 20,10 10,10</StreamGeometry>

<StreamGeometry xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
 <StreamGeometry.Transform>
  <ScaleTransform ScaleX="3" ScaleY="3" />
 </StreamGeometry.Transform>
</StreamGeometry>