[vtkusers] How to get normal information of a triangle facet in stl file

[付文宇]

Hi everyone:
   Now I can get three points coodinates of the same one triangle facet
by the help of Vladimir Lazunin. But I have another question that I cannot solve 
by myself. In stl file there is normal information of a triangle facet. I want to

get normal information too. I searched the book of vtk user's guide and web,but I

didnot find interface to get normal information of stl file in vtk. Could someone
give any suggestions?
  
 Thanks in advance for any help.
 
 Fu Wenyu 
2007.06.18