[vtkusers] How to generate a surface normal glyph for a triangle cell

[Elvis Dowson]

Hi,
         Taking the suggestion that Prasanth had made earlier about  
using vtkCellCenters, I was able to get the point normal to display a  
point normal glyph at the center of the triangle cell.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: pastedGraphic.png
Type: image/png
Size: 45046 bytes
Desc: not available
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20081009/5fed70c9/attachment.png>
-------------- next part --------------


However, i'm not sure this is the correct solution for other cases. In  
this particular case, when the cell is on a single plane, like a  
triangle cell or a plane source, the point normal will be equal to the  
surface normal. So, all that's happened is I've translated the  
generation of the point normal to the center of the cell.

I'm not so sure if the same condition will hold true if the object was  
a 3D cell, in which case the point normals need not necessarily be  
equal to the cell normal? Perhaps is this the reason why the glyphs  
are pointing in the wrong direction, i.e. because it is not a true 3D  
cell?

However, even in that case, the cell should still hold only one  
surface normal, and not three pointing in the wrong direction.

Some comments from the vtk experts would be appreciated, since this  
involves answering some fundamental properties of cells, cell normals  
and the behavior of vtkPolyDataNormals.

Best regards,

Elvis Dowson