[vtkusers] How to extract poly data from an unstructured grid

[Elvis Dowson]

Hi Frederic,
                          I want to retain the use of the unstructured  
grid, for later purposes. The only reason I want to extract the poly  
data from the unstructured grid is to compute the cell normals using  
vtkPolyDataNormals, which has a method to compute cell normals.

I'm taking a look at vtkCellDataToPointData, but can't seem to get it  
to work. When I run the program, the surface normal does not get  
displayed for the triangle cell, plus I get the following error output  
in the terminal window:

ERROR: In /Users/elvis/Tool/vtk-5.x/src/VTK/Filtering/ 
vtkDemandDrivenPipeline.cxx, line 722
vtkStreamingDemandDrivenPipeline (0x612fe70): Input port 0 of  
algorithm vtkPolyDataNormals(0x612f870) has 0 connections but is not  
optional.


Best regards,

Elvis Dowson

Example TCL code

# This example shows how to manually construct triangle cell using  
unstructured grids
# and display its surface normal.
#

package require vtk
package require vtkinteraction

# Create an unstructured grids containing a triangle cell.
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 an arrow glyph to represent the surface normal for the  
triangle cell.
# Specify the location of the glyph
vtkPolyData arrowGlyphPolyData
vtkPoints   arrowGlyphPoints
   arrowGlyphPolyData SetPoints arrowGlyphPoints
   arrowGlyphPoints InsertNextPoint 1 1 0

vtkCellDataToPointData triangleCellToPolyData
   triangleCellToPolyData SetInput aTriangleGrid
   triangleCellToPolyData PassCellDataOff

# Question: Is this mapping necessary?
vtkPolyDataMapper trianglePolyData
   trianglePolyData SetInput [triangleCellToPolyData GetPolyDataOutput]

vtkPolyDataNormals triangleCellNormals
   # TODO: Fix this
   triangleCellNormals SetInputConnection [trianglePolyData  
GetOutputPort]
   #triangleCellNormals SetInputConnection [triangleCellNormals  
GetOutputPort]
   #triangleCellNormals SetInput arrowGlyphPolyData
   triangleCellNormals ComputePointNormalsOff
   triangleCellNormals ComputeCellNormalsOn

# Specify the shape of the glyph
vtkArrowSource arrowSource

vtkGlyph3D arrowGlyph
   arrowGlyph ScalingOn
   arrowGlyph SetScaleFactor 0.7
   arrowGlyph SetVectorModeToUseNormal
   arrowGlyph SetScaleModeToScaleByVector
   arrowGlyph OrientOn
   arrowGlyph SetSourceConnection [arrowSource GetOutputPort]
   arrowGlyph SetInputConnection [triangleCellNormals GetOutputPort]

vtkDataSetMapper arrowGlyphMapper
   arrowGlyphMapper SetInputConnection [arrowGlyph GetOutputPort]

vtkActor glyphActor
   glyphActor SetMapper arrowGlyphMapper


# 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 AddActor glyphActor

ren1 ResetCamera
ren1 ResetCameraClippingRange

renWin Render

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



On Oct 9, 2008, at 10:49 AM, Frederic DANESI wrote:

> It should be easier if you build directly a polydata …
> # Create an unstructured grids containing a triangle cell.
> 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
> vtkPolyData aTrianglePoly
>   aTrianglePoly Allocate 1 1
>   aTrianglePoly InsertNextCell [aTriangle GetCellType] [aTriangle  
> GetPointIds]
>   aTrianglePoly SetPoints trianglePoints
>
> Fred.
>
>
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