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

[Elvis Dowson]

Hi,
        How can I generate a simple surface normal glyph, for a  
triangle cell. I just want to automatically compute the surface normal  
and generate an arrow to represent the direction of the surface normal  
for the triangle.

My tcl code for generating a triangle using unstructured grids is  
shown below:

package require vtk
package require vtkinteraction

# Create several unstructured grids each containing a cell of a  
different type.
vtkPoints trianglePoints
   trianglePoints SetNumberOfPoints 3
   trianglePoints InsertPoint 0 0 0 0
   trianglePoints InsertPoint 1 1 0 0
   trianglePoints InsertPoint 2 .5 .5 0
vtkTriangle aTriangle
   [aTriangle GetPointIds] SetId 0 0
   [aTriangle GetPointIds] SetId 1 1
   [aTriangle GetPointIds] SetId 2 2
vtkUnstructuredGrid aTriangleGrid
   aTriangleGrid Allocate 1 1
   aTriangleGrid InsertNextCell [aTriangle GetCellType] [aTriangle  
GetPointIds]
   aTriangleGrid SetPoints trianglePoints
vtkDataSetMapper aTriangleMapper
   aTriangleMapper SetInput aTriangleGrid
vtkActor aTriangleActor
   aTriangleActor SetMapper aTriangleMapper
   aTriangleActor AddPosition 4 0 2
   [aTriangleActor GetProperty] SetDiffuseColor .3 1 .5


# Create the usual rendering stuff.
vtkRenderer ren1
vtkRenderWindow renWin
   renWin AddRenderer ren1
   renWin SetSize 300 150
vtkRenderWindowInteractor iren
   iren SetRenderWindow renWin

ren1 SetBackground .1 .2 .4

ren1 AddActor aTriangleActor

ren1 ResetCamera
ren1 ResetCameraClippingRange

renWin Render

# render the image
#
iren AddObserver UserEvent {wm deiconify .vtkInteract}
iren Initialize
wm withdraw .


Best regards,

Elvis Dowson