[Paraview] using integrate variables between two filters

[Michael Rapson]

Dear Sven,

Thank you for that answer. I would have struggled to find that post
and both do exactly what I need.

Something that I noticed when applying step 4:
> 4) Use Calculator #2 on AppendAttributes1 to take difference (eg h1-h0).
If h1 and h0 are extracted as a single component of a vector, eg
velocity_0, I get an error when applying this calculator:

ERROR: In /home/kitware/ParaView-3.6/ParaView3/VTK/Common/vtkFunctionParser.cxx,
line 1629
vtkFunctionParser (0x3376110): Syntax error: operator expected; see position 2

ERROR: In /home/kitware/ParaView-3.6/ParaView3/VTK/Common/vtkFunctionParser.cxx,
line 1629
vtkFunctionParser (0x3376110): Syntax error: operator expected; see position 2

Warning: In /home/kitware/ParaView-3.6/ParaView3/VTK/Graphics/vtkArrayCalculator.cxx,
line 394
vtkArrayCalculator (0x3036ec0): An error occured when parsing the
calculator's function.  See previous errors.

I have seen these errors on Linux paraview 3.6.1 and 3.2.1 as well as
Mac 3.4. Interestingly enough if I set up the initial two calculators
with a scalar field, e.g. pressure, it works fine and I can later swop
the pressures to velocity_0 with out any problem. (In order to test
this I used a single .vtk file with a vector velocity a scalar
pressure and made a copy of the file copy of the file. Once the inputs
were swopped I confirmed that the difference between the velocities in
the files was zero.)

I was surprised that taking the velocities directly failed, but
specifying the pressures first and swopping seems to be a good work
around.

Thanks for the help!
Michael




On Wed, Dec 9, 2009 at 2:15 PM, Sven Buijssen
<sven.buijssen at tu-dortmund.de> wrote:
> Hi Michael,
>
> Your first question has been discussed before, e.g., here:
> http://markmail.org/message/jon3wyz3ve2rzza5
>
> Regarding your second question you're looking for the ParaView filter Resample
> with Dataset. It takes two inputs which will be your coarse and refined grid.
> See the filter's help for more details.
>
> Sven
>
>
> ----- Original Message -----
> From: Michael Rapson <rpsmic001 at gmail.com>
> To: paraview at paraview.org
> Sent: 12/09/09 12:41:12
> Subject: [Paraview] using integrate variables between two filters
>> Hi all,
>>
>> I use Paraview to post process results from finite element simulations
>> and find it very useful. There is however, one thing that seems
>> feasible but I cannot find out how to do in Paraview and I would
>> appreciate it if someone could tell me whether it is possible.
>>
>> I write data from my simulation to file as .vtk with a number of
>> variables at each mesh location (say x velocity, y velocity and
>> pressure). In Paraview I can load the file, compute result =
>> velocity_X - velocity_Y using the calculator and then integrate
>> variables to get the integral of velocity_X - velocity_Y on the mesh.
>> This is obviously not a very useful result in general, what I really
>> want is to compute velocity_X_simulation_1 - velocity_X_simulation_2,
>> where simulation 1 and 2 share the same mesh but some different
>> parameters. I can use a similar method to the one described above as
>> long as the data from both simulations is stored in the same .vtk
>> file, but is it possible to load two .vtk files into a single
>> pipeline, or to access data across pipelines for the integrate
>> variables method?
>>
>> An even more optimistic question, if the two simulations are run on
>> meshes that exist on the same domain (i.e. region in space) but have a
>> different set of nodes, say the mesh for simulation 2 is refined once
>> more than the mesh from simulation 1, is it possible for Paraview to
>> interpolate data from the less refined mesh to the more refined mesh
>> in order to compute velocity_X_simulation_1 - velocity_X_simulation_2
>> and integrate?
>>
>> The first scenario seems technically feasible, if it has been offered
>> in Paraview. Alternatively, are there specialized programs that can
>> read two .vtk files and combine their variables into a single .vtk
>> file? The second is more optimistic and couldn't be done without
>> explicitly interpolating the results from one mesh to the other. I
>> have found the Group Datasets filter, but this does not seem to quite
>> do it (the data sets are marked (partial) once grouped and calculating
>> differences fails).
>>
>> Thank you for any ideas about how I could achieve this, and also
>> confirming whether it can be done in Paraview or if I should make
>> another plan will help me to move forward.
>>
>> Regards,
>> Michael
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