[Paraview] CullBackface, Normals and Missing Triangles

[Michael Jackson]

I have a triangular mesh that is generated from an experimental  
meshing algorithm. I am using ParaView to check the mesh for  
consistency. I am trying to diagnose a potential problem that I just  
can not understand how it is happening and I am not sure if there is a  
problem in my code, the writing of the vtk file or in ParaView.
    I have a triangle surface mesh where a few of the triangles are  
not visible if you render by "Cull Backface" in the Display tab.  
Usually this means the triangle winding is backwards so I ran the  
"Normal Glyphs" filter and all the arrows are consistently pointing  
the correct direction, even for the "missing" triangle. For better or  
worse, I also use the T=2V-4 equation to try and figure out of the  
surface is "water tight" which it should be and the equation validates  
that. I don't really know what else to check? Selecting "CELLS" and  
showing the CELL_DATA values for the cells shows a value floating on  
the missing triangle so I am reasonably convince there is a triangle  
there.
    So why would the triangle disappear when I render with "Cull  
Backface" but the normal for the triangle say that I should be looking  
at the front face?

    Ideas, suggestions and thoughts are welcome.

Thanks for any help.
___________________________________________________________
Mike Jackson                      www.bluequartz.net
Principal Software Engineer       mike.jackson at bluequartz.net
BlueQuartz Software               Dayton, Ohio