[Paraview] extract surface of multiblock mesh

[Chris Kees]

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
>
>
>