[vtkusers] How to use vtkCellDerivatives with unstructured grid image

[Seth Gilchrist]

Hello,
Sorry to bump, but I'm still struggling with this and can't find any
good help in my books or online.  I have the "VTK Users Guide" and
"The Visualization Toolkit: An Object-Oriented Approach to 3-D
Graphics," but neither of them is any help in this case.

Can anybody help with this question?  Examples, hints, whatever you
can do is really appreciated.

Cheers,
Seth

Previous message:
Hello,
I have the unstructured grid image printed at end of this email, with two
point data sets "Dispamcement" (vectors) and "Optimizer Value" (scalors).  I
want to use vtkCellDerivatives to calculate the strain tensors from the
"Displacement" point data.  I can't figure out how to input the data into
vtkCellDerivatives.  I have tried:

vtkCellDerivatives  *dCalc = vtkCellDerivatives::New();
dCalc->
SetTensorModeToComputeStrain();
dCalc->SetInput( image->GetPointData()->GetArray("Displacement") );
dCalc->Update();

and

vtkCellDerivatives  *dCalc = vtkCellDerivatives::New();
dCalc->SetTensorModeToComputeStrain();
dCalc->SetInput(image);
dCalc->SetInputArrayToProcess( [uh...I get lost here, I've tried a lot of
things]  );
dCalc->Update();

I either can't get it to compile, or the output of the filter is the same as
the input.

Can anybody point me in the right direction?

Thanks,
Seth

The cells in the image are quadratic tets.

image->Print( std::cout )...

vtkUnstructuredGrid (0x10f1150)
 Debug: Off
 Modified Time: 268
 Reference Count: 1
 Registered Events: (none)
 Source: (none)
 Information: 0x10e6130
 Data Released: False
 Global Release Data: Off
 UpdateTime: 269
 Release Data: Off
 UpdateExtent: Not Initialized
 Update Number Of Pieces: 1
 Update Piece: 0
 Update Ghost Level: 0
 MaximumNumberOfPieces: 1
 RequestExactExtent: Off
  Field Data:
   Debug: Off
   Modified Time: 252
   Reference Count: 1
   Registered Events: (none)
   Number Of Arrays: 0
   Number Of Components: 0
   Number Of Tuples: 0
 Number Of Points: 81
 Number Of Cells: 30
 Cell Data:
   Debug: Off
   Modified Time: 259
   Reference Count: 1
   Registered Events: (none)
   Number Of Arrays: 0
   Number Of Components: 0
   Number Of Tuples: 0
   Copy Tuple Flags: ( 1 1 1 1 1 0 1 )
   Interpolate Flags: ( 1 1 1 1 1 0 0 )
   Pass Through Flags: ( 1 1 1 1 1 1 1 )
   Scalars: (none)
   Vectors: (none)
   Normals: (none)
   TCoords: (none)
   Tensors: (none)
   GlobalIds: (none)
   PedigreeIds: (none)
 Point Data:
   Debug: Off
   Modified Time: 268
   Reference Count: 1
   Registered Events: (none)
   Number Of Arrays: 2
   Array 0 name = Displacement
   Array 1 name = Optimizer Value
   Number Of Components: 4
   Number Of Tuples: 81
   Copy Tuple Flags: ( 1 1 1 1 1 0 1 )
   Interpolate Flags: ( 1 1 1 1 1 0 0 )
   Pass Through Flags: ( 1 1 1 1 1 1 1 )
   Scalars: (none)
   Vectors: (none)
   Normals: (none)
   TCoords: (none)
   Tensors: (none)
   GlobalIds: (none)
   PedigreeIds: (none)
 Bounds:
   Xmin,Xmax: (57.5, 67.3)
   Ymin,Ymax: (45.7, 56.7)
   Zmin,Zmax: (41.7, 59.1)
 Compute Time: 283
 Number Of Points: 81
 Point Coordinates: 0x10e7890
 Locator: 0
 Number Of Pieces: 1
 Piece: 0
 Ghost Level: 0