public static void ReverseNormals(MeshGeometry3D inputmesh)
{
System.Windows.Media.Int32Collection indices = inputmesh.TriangleIndices.Clone();
inputmesh.TriangleIndices.Clear();
foreach (var v in indices.Reverse())
{
inputmesh.TriangleIndices.Add(v);
}
indices = null;
}