public static Dictionary <string, Visual3D> ColladaToVisual3D(this XmlDocument doc)
        {
            doc.ColladaToXaml();
            XmlElement  e  = doc.GetElementsByTagName("library_visual_scenes")[0] as XmlElement;
            XmlNodeList nl = e.GetElementsByTagName("visual_scene");
            Dictionary <string, Visual3D> d = new Dictionary <string, Visual3D>();

            foreach (XmlElement el in nl)
            {
                Visual3D v = el.ToVisual3D();
                if (v != null)
                {
                    v.SetLight();
                    d[el.GetAttribute("id")] = v;
                }
            }
            return(d);
        }