[Paraview-developers] Passing values between filters

[Oliver Fernandes]

Thanks for the help, Cory! I will try out vtkFieldData member.
Just for educational reasons, is there a reason to learn about vtkInformation?
Or what would be a use case for that?
(No details, just want to know what it's intended use is)

Thanks again for the quick reply!
-Oli

________________________________________
Von: Cory Quammen <cory.quammen at kitware.com>
Gesendet: Donnerstag, 24. März 2016 14:03
An: Oliver Fernandes
Cc: paraview-developers at paraview.org
Betreff: Re: [Paraview-developers] Passing values between filters

Oliver,

I often pass these kinds of values through the vtkUnstructuredGrid's
field data. Field data consists of data arrays, just like point or
cell data, but the number of elements in the arrays is not expected to
correspond to the number of points or cells, as is the case with point
and cell data arrays.

You can get the field data with

vtkUnstructuredGrid::GetFieldData()

Docs for vtkFieldData are here:

http://www.vtk.org/doc/nightly/html/classvtkFieldData.html

The nice thing with this approach is that the field data gets passed
automatically through most filters, so you'll be able to pick up the
values set by your reader in your writer, for example.

HTH,
Cory

On Thu, Mar 24, 2016 at 3:56 AM, Oliver Fernandes
<Oliver.Fernandes at visus.uni-stuttgart.de> wrote:
> Hello all,
>
> So I wrote a couple of ParaView filters in C++, namely a reader A for a
> custom file format deriving from vtkUnstructuredGridAlgorithm, and a filter
> B that takes two of these outputs as input and does some calculation on
> them.
>
> Everything is working fine, but now I noticed that I need to pass a single
> string value (and 3-4 numbers) from each reader to the actual filter B doing
> stuff.
> A use case would be, for example, passing the input data filename from a
> reader to a filter on to a writer plugin, which can use it to come up with
> an appropriate output filename.
>
> Now the work-around I'm using at the moment to pass these data to the filter
> B is abusing CellData or PointData arrays of the vtkUnstructuredGrid
> generated in A. Needles to say this is not very elegant and creates other
> problems too (memory issues), and I'm fairly sure there is a better way to
> do it.
>
> I think that somehow I need to create an appropriate vtkInformationKey
> storing the data.
> However, everything I tried seems to be wrong, the key seems to disappear in
> the pipeline between the filters.
>
> Here is some pseudocode snippet to show what I tried to add a value to an
> vtkInformation.
> Here the reader class A:
> <code>
> class A : vtkUnstructuredGridAlgorithm {
>   static vtkInformationStringKey* MYSTRING();
>    ...
> }
>
> vtkInformationKeyMacro(A, MYSTRING, String);
>
> A::RequestInformation(...) {
>   vtkSmartPointer<vtkInformation> outInfo =
> outputVector->GetInformationObject(0);
>   outInfo->Set(A::MYSTRING(),"test");
> }
> </code>
> And the filter class B:
> <code>
> #include "classA.h"
> class B : vtkUnstructuredGridAlgorithm {
>    ...
> }
>
> B::RequestInformation(...) {
>   vtkSmartPointer<vtkInformation> inInfo =
> inputVector[0]->GetInformationObject(0);
>   if (!inInfo->Has(A::MYSTRING()))
>      std::cout << "fail" std::endl;
>
> }
> </code>
> I keep getting fails printed to my console :(
>
> So here is the question(s):
> A colleague of mine mentioned to check out the python interface, but I
> assume this can be done within vtk?
> Is this the correct approach using vtkInformation?
>
> -If yes, what am I doing wrong? I derived my code from an example which I
> can't seem to find anymore...
> Can someone give me a detailed explanation of the steps necessary, or a well
> commented example?
>
> -If no,is there a better, or more paraviewesque way to do it (not the python
> way), and can I get hint at what I need to look at please?
> Any other comments on how to pass user defined data along the pipeline?
>
> Thanks a lot for the help,
> Oli
>
> P.S.: I'm using ParaView 5.0.0
>
>
>
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--
Cory Quammen
R&D Engineer
Kitware, Inc.