[vtkusers] Hexahedrons in unstructured grids with bad aspect ratios

[Sarah Macumber]

Thanks for your help, I found the issue!  Since I am developing in the Dot Net Framework .h files are not wrapped and hence unavailable thus we had our own enumeration tye for vtkCellType.h which turned out to be incorrect.  It works fine now.
Thanks Sarah

________________________________

From: Bryn Lloyd [mailto:blloyd at vision.ee.ethz.ch]
Sent: Tue 7/15/2008 1:25 AM
To: Sarah Macumber
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] Hexahedrons in unstructured grids with bad aspect ratios



I tried your example - I can see the cell in paraview. Don't know why
you can't.

Here is the python script I used to create the cell:

newPoints = vtkPoints()
newPoints.InsertNextPoint(2.9892,      0.0,          0.0)
newPoints.InsertNextPoint(2.9299,      0.0,           0.05)
newPoints.InsertNextPoint(2.3707,      0.981,       0.05)
newPoints.InsertNextPoint(2.372,        0.9828,     0.0)
newPoints.InsertNextPoint(3.2342,      0.0,           0.0)
newPoints.InsertNextPoint(3.174,        0.0,           0.05)
newPoints.InsertNextPoint(2.59248,    1.0738,      0.05)
newPoints.InsertNextPoint(2.584,        1.070,       0.0)

newCells = vtkCellArray()
pids = vtkIdList()
pids.InsertNextId(0)
pids.InsertNextId(1)
pids.InsertNextId(2)
pids.InsertNextId(3)
pids.InsertNextId(4)
pids.InsertNextId(5)
pids.InsertNextId(6)
pids.InsertNextId(7)
newCells.InsertNextCell( pids )

usGrid = vtkUnstructuredGrid()
usGrid.SetPoints(newPoints)
usGrid.SetCells(12, newCells) # VTK_HEXAHEDRON=12

writer = vtkUnstructuredGridWriter()
writer.SetInput(usGrid)
writer.SetFileName("hex.vtk")
writer.Update()

quality = vtkMeshQuality();
cell = usGrid.GetCell(0)
print "HexShape \t\t", quality.HexShape(cell)
print "HexJacobian \t\t", quality.HexJacobian(cell)
print "HexMaxEdgeRatio \t\t", quality.HexMaxEdgeRatio(cell)


Cheers, Bryn






Sarah Macumber wrote:
> Does VTK have any known problem drawing Hexahedrons with bad aspect ratios?  I can get VTK to draw the points but not the cells.  I have been going over my data for a while & can't find any problems with the data or the cells.  I included an example cell below.
> 
> Any help is appreciated,
> Sarah
> 
> ID          X              Y              Z
> 0           2.9892      0.0          0.0
> 16         2.9299      0.0           0.05
> 17         2.3707      0.981       0.05
> 1           2.372        0.9828     0.0
> 16000    3.2342      0.0           0.0
> 16016    3.174        0.0           0.05
> 16017    2.59248    1.0738      0.05
> 16001    2.584        1.070       0.0
> 
> With a hexahedron cell ID list of :
> 0 16 17 1 16000 16016 16017 16001
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--
-------------------------------------------------
Bryn Lloyd
Computer Vision Laboratory
ETH Zürich, Sternwartstrasse 7
CH - 8092 Zürich, Switzerland
Tel: +41 44 63 27690
Fax: +41 44 63 21199
-------------------------------------------------