[Paraview] Pipeline update with Catalyst

Andy Bauer andy.bauer at kitware.com
Tue Feb 7 10:05:14 EST 2017 

The pipeline is update mechanism is often called a lazy update scheme
meaning only do the requested work and no more. If the UpdateProducers()
method automatically updated all of the filters there would be a lot of
unneeded work that would be done. Think about a Catalyst script that
branched into 3 separate outputs with a lot of work done in each branch. If
only one output was wanted during a time step that could potentially be a
lot of extra, unneeded work.

As for parallel communication in Catalyst, again it's an efficiency thing
meaning that if we can avoid communication we may as well do it. In
interactive mode (i.e. through the GUI) it's useful to know things like the
total number of points and cells, bounds and field ranges which requires
communication. In Catalyst this information isn't usually needed so that's
the type of information that would need to be globally communicated. For
filters like the Integrate Attributes filter, you should get the same
behavior in the GUI as in Catalyst with regard to parallel output since the
filter itself does not know how ParaView is running. Some filters (e.g.
Resample with Dataset) though only have non-empty results on process 0 so
it is definitely safest to check filters like Integrate Attributes in
parallel.

Cheers,
Andy


On Tue, Feb 7, 2017 at 7:51 AM, Gallagher, Timothy P <
tim.gallagher at gatech.edu> wrote:

> Thanks Andy,
>
>
> I had a feeling the pipeline had to be manually updated. I thought maybe
> the UpdateProducers also updated the pipeline. Thanks for clarifying that.
>
>
> I also have the same concern about the value stored in each block's
> CellData field. I couldn't find any documentation that indicates how the
> IntegrateVariables filter distributes the data. But, looking at the block
> VTK files that are written out, they all contain the same value of Area so
> I think a global reduction is done in the filter and all blocks have the
> total values. I could be wrong though.
>
>
> Thanks again,
>
>
> Tim
>
>
> ------------------------------
> *From:* Andy Bauer <andy.bauer at kitware.com>
> *Sent:* Tuesday, February 7, 2017 7:44 AM
> *To:* Gallagher, Timothy P
> *Cc:* paraview at paraview.org
> *Subject:* Re: [Paraview] Pipeline update with Catalyst
>
> Hi Tim,
>
> The short answer is that  you need to do coprocessor.Pipeline.flameArea.UpdatePipeline()
> before checking for the area. You also may need to use MPI to do the global
> sum or broadcast of the value since I think that value will either just
> have local values or maybe just the proper global value on processor 0. You
> should have access to mpi4py in the Python script in order to do that.
>
> The long answer is that ParaView & VTK use a demand-driven pipeline design
> meaning that until something explicitly tells a pipeline to update it
> won't. For the Catalyst scripts this is done in the
> coprocessor.WriteData(), coprocessor.WriteImages() and coprocessor.DoLiveVisualization()
> calls for each output that is required (e.g. for a writer that is supposed
> to output at that time step but not for other writers that are not supposed
> to output at that time step). You can manually force a filter to update by
> using the UpdatePipeline() method which will update that pipeline along
> with everything it depends on. It won't update any filters though that
> don't have an effect on it computing its requested information which means
> that for the flameArea filter it won't affect any writers or image output
> stuff which is what you want.
>
> There is some information on Catayst script details at
> https://blog.kitware.com/anatomy-of-a-paraview-catalyst-python-script/
> but I don't think that contains this information.
> <https://blog.kitware.com/anatomy-of-a-paraview-catalyst-python-script/>
> Anatomy of a ParaView Catalyst Python Script | The Kitware ...
> <https://blog.kitware.com/anatomy-of-a-paraview-catalyst-python-script/>
> blog.kitware.com
> Introduction. ParaView Catalyst has yielded some amazing results. Such
> results include iso-surfacing and generating images with 256K Message
> Passing Interface (MPI ...
>
>
> Cheers,
> Andy
>
> On Tue, Feb 7, 2017 at 7:14 AM, Gallagher, Timothy P <
> tim.gallagher at gatech.edu> wrote:
>
>> Hello again,
>>
>>
>> I am working on a pipeline using Catalyst that writes data only when
>> features are detected. The idea is to have a 3D contour generated in the
>> pipeline, and when it is big enough, start recording data. There is a long
>> lead-up to when the features appear, and then they disappear rapidly, so I
>> would like to only collect data when the features are present.
>>
>>
>> To that end, my DoCoProcessing() function has something that checks the
>> 'Area' value in the CellData of an IntegrateVariables filter. The full
>> function is below. However, this doesn't ever write any images or data. It
>> also doesn't throw any errors, so I have a feeling the pipeline isn't
>> actually evaluated/updated after the call to UpdateProducers.
>>
>>
>> So, my question -- at what point in the DoCoProcessing function is the
>> pipeline actually evaluated? Do all the filters execute when the
>> UpdatedProducers function is called? Or do they only update when the
>> outputs to which they are connected are called, ie. WriteData and
>> WriteImages?
>>
>>
>> Thanks,
>>
>>
>> Tim
>>
>>
>> def DoCoProcessing(datadescription):
>>     "Callback to do co-processing for current timestep"
>>     global coprocessor
>>     global lastTime
>>     global deltaT
>>
>>     # Update the coprocessor by providing it the newly generated
>> simulation data.
>>
>>
>>     # If the pipeline hasn't been setup yet, this will setup the
>> pipeline.
>>
>>
>>     coprocessor.UpdateProducers(datadescription)
>>
>>     curTime = datadescription.GetTime()
>>
>>     if curTime >= lastTime + deltaT:
>>       lastTime = curTime
>>
>>       if coprocessor.Pipeline.flameArea.CellData['Area'] > 1e-9:
>>         # Write output data, if appropriate.
>>
>>
>>
>>         coprocessor.WriteData(datadescription);
>>
>>         # Write image capture (Last arg: rescale lookup table), if
>> appropriate.
>>
>>
>>         coprocessor.WriteImages(datadescription,
>> rescale_lookuptable=False)
>>
>>         # Live Visualization, if enabled.
>>
>>
>>
>>         coprocessor.DoLiveVisualization(datadescription, "localhost",
>> 22222)
>>
>>
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