[Paraview] extract surface of multiblock mesh

[Berk Geveci]

The right way to deal with this situation is to mark the ghost cells
as ghost. If you create a cell array called vtkGhostLevels and assign
0 to inside cells and 1 to ghost cells, you should not need
MergeBlocks or CleanToGrid. Note that this array has to be of type
unsigned char. There are actual benefits to keeping ghost levels since
some algorithms will produce better results.

-berk

On Thu, Apr 2, 2009 at 6:37 PM, Chris Kees
<christopher.e.kees at usace.army.mil> wrote:
> I turned off the overlapping domain decomposition (ghost cells) for a simple
> problem and the sequence
>
> MergeBlocks->CleantoGrid->ExtractSurface->Clip
>
> shows just the physical boundary of the problem (clipped open so you can see
> inside). Also volume visualization and streamline calculation works with no
> processor boundary artifacts.
>
> From what I understand, there are no filters in paraview or abstractions in
> the XDMF data model  at this time that will allow paraview to read in
> overlapping blocks and really make use of the ghost cells correctly. For now
> truncating our output to only "owned" elements will solve our problems.
> Thanks again for the help.
>
> Chris
>
> On Mar 30, 2009, at 2:06 PM, Chris Kees wrote:
>
>> Thanks for  the help. I also tried suggestions from Paul, Ken, and Berk,
>> but it does seem that I'm stuck right now unless I provide ParaView with
>> more information. Since streamlines are computed correctly on the current
>> multiblock mesh I just generated the mesh on a single processor and used
>> ExtractSurface->Clip on that mesh to visualize the geometry around the
>> streamlines from the multiblock grid.
>>
>> On the first method: Each of my UnstructuredGrids in the Multiblock Grid
>> is a subdomain in an overlapping decomposition of the domain. Each of the
>> subdomains has several elements of overlap (the layer of ghost cells is more
>> than one element thick).  Presumably the streamline generation works now on
>> the multiblock grid because the overlap is loaded into ParaView. Is there a
>> way I can just set a cell-centered attributed to identify the ghost cells so
>> that surface extraction and volume visualization will work too?  Currently
>> volume visualization of the multiblock grid shows only a single subdomain
>> and volume visualization after MergeBlocks shows the whole domain but with
>> overlap regions being more opaque.
>>
>> On your other method, we have both the external boundary mesh and a
>> pre-mesh polygonal representation of the boundaries available in the
>> simulator. You are suggesting that I just dump one of those to a valid
>> ParaView format as well, is that correct?
>>
>> Chris
>>
>> On Mar 30, 2009, at 9:14 AM, Jean Favre wrote:
>>
>>> Chris Kees wrote:
>>>>
>>>> So far I've tried MergeBlocks->ExtractSurface->FeatureEdges->Clip and
>>>> various permutations that I've seen in previous posts and the wiki,
>>>> but I always end up with the  surfaces on the interior of the tank as
>>>> if it still sees each subdomain as a closed surface.
>>>
>>> In fact, it seems to me that ParaView does the best it can. Your
>>> unstructured mesh is partitioned in 512 pieces and [presumably], you did
>>> not specify ghost-cells at the partition boundaries. Without
>>> ghost-cells, ParaView has no information to help decide whether an
>>> outside face looks towards the outside world, or to another partition. I
>>> don't think any combination of filters would help you. Removing
>>> duplicate points may only remove duplicate fake boundaries, but these
>>> fake boundaries must be removed all together.
>>>
>>> I use two methods to achieve what you want. Ghost-cells, or another
>>> multi-piece object containing the different boundary types (solid,
>>> symmetries, inflow, outflow, etc) stored as vtkPolyData. These are read
>>> in from the models on disk.
>>>
>>> Jean --
>>> Swiss National Supercomputing Center
>>>
>>>
>>>
>>
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