[vtkusers] PVTS, Multiblock or Both

Philip Sakievich psakievich at gmail.com
Thu Dec 22 00:07:07 EST 2016

I'm unclear on how to work with this if I don't specify the local extent.
In my code I am subdividing my computational domain so the data is unique
on each processor, doing work and then dumping the results.  It is
completely distributed and the processors don't share any data except on
the boundaries.  I already know the global and local extents and now I need
the local extent in the pvts to line up with the other portions of my
code.  I don't want the pipeline to give me the local extent unless I can
get it to match the extent I've already specified.

 At this point, it is almost seeming easier to write a script that writes
the *pvts for me instead of using the pipeline, but it frustrates me that I
can't get the pipeline to do what I want. I'm trying to learn VTK in a
broad sense in my spare time. However, for this specific problem the only
thing I need is for the PVTS file to have the LocalExtents match my
datasets on each of the processors. If I can just solve this all of my
problems will be over. I am still wrapping my head around the pipeline
concept, but it has been a struggle since there aren't many examples for
the problem I'm trying to work with.  I'm actually not doing any rendering.
I'm just managing IO.

I looked at the source you mentioned, but I'm not sure where I am supposed
to interact with the RequestInformation request. I'm assuming it will be in
the filter that is the input to vtkXMLPStructuredGridWriter, but I haven't
really worked with any filters since I've only been doing IO.  With the
programmable filter example
I can get it to write local extents that differ from the WholeExtent but
they do not match my datasets. (In this case I just copied the execute

Also, I don't really see why it is necessary to specify the WholeExtent in
RequestInformation.  I can specify the WholeExtent via
vtkStructuredGrid.SetDimensions(), or SetExtent and it works fine.  It's
just that the LocalExtents aren't correct. I think I'm really hitting a
roadblock because I don't understand how the parallel writer and the
partitioning works with the pipeline.

Can you provide some specifics on how the partitioning is supposed to work
and/or help me modify the code in my previous example to do what I'm
looking for? Either that or specify an open source code that has
implemented vtkXMLPStructuredGridWriter that I can review.  My application
is a CFD solver and it's post processing routines.

On Mon, Dec 19, 2016 at 7:18 AM, Andy Bauer <andy.bauer at kitware.com> wrote:

> You need to specify the WholeExtent in the RequestInformation request.You
> actually don't specify the local extent, the pipeline will give you that
> for a source. I'd recommend looking at the Imaging/Core/vtkRTAnalyticSource.cxx
> class in VTK to see how it's done as a source.
> On Sun, Dec 18, 2016 at 1:16 AM, Philip Sakievich <psakievich at gmail.com>
> wrote:
>> Andy and community,
>> I have read about the concept of whole extent vs extent, but the one
>> thing I don't seem to be able to determine is how to set the  whole extent
>> to be different.  I tried using vtkStructuredGrid.Crop() but nothing is
>> happening.
>> In the code snippet below, I have previously declared points local to
>> each processor.  I now want to populate a structured grid and write a *pvts
>> that ties them all together.  When I run this code the pvts writes itself
>> and the files, but they all have the same whole extent and extent.  Nothing
>> is cropped to the desired local extent.  What am I doing wrong?  How do I
>> specify a whole extent that is uniform across all processors, and a local
>> extent that is specific to each one?
>> #create grid and filter for processing to writer
>> pf=vtk.vtkProgrammableFilter()
>> sg=vtk.vtkStructuredGrid()
>> #set extent global
>> sg.SetExtent(0,15,0,32,0,15)
>> #set extent local
>> if rank==0:
>>    lE=np.array([0,8,0,32,0,8],dtype=int)
>>    sg.Crop(lE)
>> if rank==1:
>>    lE=np.array([0,8,0,32,7,15],dtype=int)
>>    sg.Crop(lE)
>> if rank==2:
>>    lE=np.array([7,15,0,32,0,8],dtype=int)
>>    sg.Crop(lE)
>> if rank==3:
>>    lE=np.array([7,15,0,32,7,15],dtype=int)
>>    sg.Crop(lE)
>> sg.SetPoints(pnts)
>> pf.SetInputData(sg)
>> writer=vtk.vtkXMLPStructuredGridWriter()
>> writer.SetInputConnection(pf.GetOutputPort())
>> writer.SetController(contr)
>> writer.SetDataModeToAscii()
>> writer.SetFileName('testgrid.pvts')
>> writer.SetNumberOfPieces(nranks)
>> writer.SetStartPiece(rank)
>> writer.SetEndPiece(rank)
>> writer.Write()
>> Thanks,
>> Phil
>> On Tue, Dec 13, 2016 at 7:31 AM, Andy Bauer <andy.bauer at kitware.com>
>> wrote:
>>> Hi,
>>> I would recommend using the pvts format since that is the best format
>>> for storing structured grids. If you read it back in it will know how to
>>> properly partition the data set for different amounts of processes as well
>>> as do things like ghost cells, extract surfaces, etc.
>>> For topologically structured grids like vtkStructuredGrid there are two
>>> types of extents, "whole extent" describes the beginning and ending node
>>> (inclusive) in each direction for the entire grid while "extent" refers to
>>> each process's (or pieces if you're serial but doing streaming) partition
>>> of the grid. I believe this should be explained in the VTK User's Guide
>>> which is now available for free as a pdf download.
>>> Cheers,
>>> Andy
>>> On Tue, Dec 13, 2016 at 10:21 AM, Philip Sakievich <psakievich at gmail.com
>>> > wrote:
>>>> Greetings,
>>>> I am reasonably new to vtk and I am mainly using it to manage datasets
>>>> on structured grids.
>>>> I am trying to write data for a structured grid in parallel python via
>>>> MPI.  Each process has a separate portion of the grid, and I'm trying to
>>>> figure out how to set up the write process. I was following this example:
>>>> http://www.vtk.org/gitweb?p=VTK.git;a=blob;f=IO/ParallelXML/
>>>> Testing/Python/testParallelXMLWriters.py
>>>> But then I realized that in this case each process has the entire grid,
>>>> and each processor is just writing a portion of the data it contains.  So
>>>> do I need to use a multiblock data set?  Can someone please provide a
>>>> simple example of how to write a structured grid in parallel provided each
>>>> process has the local extent correctly specified?
>>>> Thanks
>>>> --
>>>> Phil Sakievich
>>>> PhD Candidate - Mechanical Engineering
>>>> Arizona State University - Ira A. Fulton School for Engineering of
>>>> Matter Transport and Energy
>>>> Tempe, Arizona
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>> --
>> Phil Sakievich
>> PhD Candidate - Mechanical Engineering
>> Arizona State University - Ira A. Fulton School for Engineering of Matter
>> Transport and Energy
>> Tempe, Arizona

Phil Sakievich

PhD Candidate - Mechanical Engineering
Arizona State University - Ira A. Fulton School for Engineering of Matter
Transport and Energy
Tempe, Arizona
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