[Paraview-developers] Guide to using ghost levels (old style)

[Dan Lipsa]

Great. Also note there is a UPDATE_NUMBER_OF_GHOST_LEVELS information that
tells you how many ghost levels you need to read and/or create - that
depends on your pipeline.
I would also look at one of the parallel ParaView/VTK readers to see what
they do.

Dan


On Mon, Jul 6, 2015 at 2:36 PM Schlottke-Lakemper, Michael <
m.schlottke-lakemper at aia.rwth-aachen.de> wrote:

>  Hi Dan,
>
>  Thanks a lot for this clarification - this should be enough information
> for us to get started.
>
>  Indeed, our reader plugin is designed to be used in a parallel fashion.
> Due to the size of the grid/data files, we typically use O(10)-O(1000) MPI
> ranks for pvserver. Currently we use the D3 filter if we need smooth
> gradients/statistics across domain boundaries, but the D3 filter does not
> scale well beyond a hundred or so cores.
>
>  Michael
>
>   On 06 Jul 2015, at 18:16 , Dan Lipsa <dan.lipsa at kitware.com> wrote:
>
>  Hi Michael,
> Yes, indeed this is how you would do it. I believe the array has to be
> unsigned char array though. On the first layer of ghost cells you store a
> 1, on the second layer you store a 2 and so on.
> (we just set a bit for the new version, so we don't store information
> about how many layers we have)
>
>  Also note that ghost cells are only useful if your reader reads
> different parts of the dataset on different mpi processors. If you split
> your dataset on different mpi nodes latter on, this is when you need to add
> ghost cells (because this is when you know how your data is split). If you
> run on a single processor ghosts cells are not used.
>
>  Dan
>
>
>  On Mon, Jul 6, 2015 at 11:43 AM Schlottke-Lakemper, Michael <
> m.schlottke-lakemper at aia.rwth-aachen.de> wrote:
>
>> Hi Dan,
>>
>>  Thank you for your answer. From a first impression, it seems like the
>> only really open question right now is how to generate the “vtkGhostLevels”
>> array if I am working with an vtkUnstructuredGrid in my custom reader
>> plugin? “GenerateGhostLevelArray” in vtkDataSet seems to be only relevant
>> for structured grids. Maybe I just need to create a vtkIntArray myself, add
>> it as a cell array, and name it “vtkGhostLevels”?
>>
>>  Regards,
>>
>>  Michael
>>
>>
>>  On 06 Jul 2015, at 17:10 , Dan Lipsa <dan.lipsa at kitware.com> wrote:
>>
>>  Hi Michael,
>> I am not aware of a guide to the old way of storing/accessing ghost cells
>> but I'll be happy to try to answer any specific questions you may have.
>> I can also add a link in the blog to the document if someone points it
>> out.
>>
>>  Dan
>>
>>
>>  On Sun, Jul 5, 2015 at 4:47 AM Schlottke-Lakemper, Michael <
>> m.schlottke-lakemper at aia.rwth-aachen.de> wrote:
>>
>>> Dear all,
>>>
>>>  this (http://www.kitware.com/blog/home/post/856) excellent blog post
>>> details how to use the vtkGhostLevels with the next ParaView release.
>>> However, it focuses on the changes in comparison to the previous way of
>>> doing things. Thus I am wondering if there is a comprehensive guide online
>>> that describes in a little more depth how to properly use ghost levels in
>>> the “old” (or current as of PV 4.3.1) way?
>>>
>>>  Thanks a lot in advance
>>>
>>>  Michael
>>>
>>>
>>>        --
>>> Michael Schlottke-Lakemper
>>>
>>>  SimLab Highly Scalable Fluids & Solids Engineering
>>> Jülich Aachen Research Alliance (JARA-HPC)
>>> RWTH Aachen University
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>>> Germany
>>>
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>>> Mail: m.schlottke-lakemper at aia.rwth-aachen.de
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>>
>
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