[vtkusers] Tensor glyphs

[Jose Paulo Moitinho de Almeida]

Hello 

I would like to use the capabilities of vtkTensorGlyph in such a way that the 
information regarding not only the value, but also the sign of the 
eigenvectors is transmitted. 

An example explains better the idea: If (for a 2D case) the eigenvectors are 
{2;1} or {-2;1} the representation (if I use vtkAxes as the glyph) is 
something like this for both tensors:

   |
-------
   |

The sign of the eigenvector can be represented by adding an arrow that points 
outwards  on inwards:

    ^             ^
    |             |
<-------->   >---------<
    |             |
    v             v

(This can be done with other glyphs, eg cones)

Any suggestions on how to (efficiently) do this?

I realize that vtkGlyph3D allows to index a glyph in a table according to a 
scalar value. Is doing so for each eigendirection a reasonable compromise? 
There will be no orientation problems?

Thanks

Ze Paulo