I believe vtkDistributedDataFilter will always return with global point ids (a
mapping from local point ids to global point ids), although it might pass them
if they already exist. So dd->GetOutput()->GetPointData()->GetGlobalIds()
should return the array that gives this mapping.
Ghost cells are only created on demand, and this is usually done by pipeline
convention. If you have a filter that needs a layer of ghost cells, it should
override the RequestUpdateExtent method to increment the value of
UPDATE_NUMBER_OF_GHOST_LEVELS from the output information to the input
information. This method would look something like this.
int vtkDistributedDataFilter::RequestUpdateExtent(
vtkInformation *vtkNotUsed(request),
vtkInformationVector **inputVector,
vtkInformationVector *outputVector)
{
// get the info objects
vtkInformation *inInfo = inputVector[0]->GetInformationObject(0);
vtkInformation *outInfo = outputVector->GetInformationObject(0);
int piece, numPieces, ghostLevels;
// We require an extra layer of ghost cells from upstream.
piece = outInfo->Get(vtkStreamingDemandDrivenPipeline::UPDATE_PIECE_NUMBER());
numPieces =
outInfo->Get(vtkStreamingDemandDrivenPipeline::UPDATE_NUMBER_OF_PIECES());
ghostLevels =
outInfo->Get(vtkStreamingDemandDrivenPipeline::UPDATE_NUMBER_OF_GHOST_LEVELS());
inInfo->Set(vtkStreamingDemandDrivenPipeline::UPDATE_PIECE_NUMBER(), piece);
inInfo->Set(vtkStreamingDemandDrivenPipeline::UPDATE_NUMBER_OF_PIECES(),
numPieces);
inInfo->Set(vtkStreamingDemandDrivenPipeline::UPDATE_NUMBER_OF_GHOST_LEVELS(),
ghostLevels);
return 1;
}
The operation of the RequestData method should also strip off this layer of
ghost cells. It might be possible to request a layer of ghost cells by setting
UPDATE_NUMBER_OF_GHOST_LEVELS at the bottom of the pipeline, but I'm not
totally sure how to make that work. It's probably easier (or at least cleaner)
to do it from within a filter.
-Ken
From: Andrew Parker
<[email protected]<mailto:[email protected]>>
Date: Tuesday, November 6, 2012 8:25 AM
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: [EXTERNAL] [Paraview] vtkDistributedDataFilter and ghost cells
Hi,
Hope you can help. I have some code running in parallel, that by other means I
have constructed nprocs worth of vtkRectilinearGrids, one per process. Each of
which is a valid nprocs-worth of the whole serial mesh, I've check this and I
am happy with that i.e. it's partitioned properly and nothing is missing. I
need the following information to process my data in parallel:
1) I would like the local -> global cell mapping between the local rgrid and
the corresponding global single mesh.
2) I would like to know which cells are on processor boundaries for parallel
exchange purposes.
3) I would like all the double arrays per processor to be "expanded" by the
amount of (1 level of) ghost cells such that I can properly do the computations
I want with the ability to exchange only those additional cells given the local
to global mapping.
I have tried from the examples to use the following code, which I call on every
process, each of which has it's own local rgrid as I said. I do the following:
vtkSmartPointer<vtkDistributedDataFilter> dd =
vtkSmartPointer<vtkDistributedDataFilter>::New();
dd->SetInput(rgrid);
dd->SetController(getVtkController());
dd->SetBoundaryModeToSplitBoundaryCells();
//dd->SetBoundaryModeToAssignToOneRegion();
//dd->SetBoundaryModeToAssignToAllIntersectingRegions();
dd->UseMinimalMemoryOff();
dd->Update();
vtkPieceScalars *ps = vtkPieceScalars::New();
ps->SetInputConnection(dd->GetOutputPort());
ps->SetScalarModeToCellData();
vtkDataSetSurfaceFilter *dss = vtkDataSetSurfaceFilter::New();
dss->SetInputConnection(ps->GetOutputPort());
The dd object works fine and writing its contents out on each processor gives
nprocs worth of meshes, each of which look slightly different to the way I've
partitioned them up, but sum to the same serial mesh so I am happy with that
working correctly. But I can't for the life of me figure out how to obtain
local to global cell mappings, allocate ghost cells, or work out how to
exchange data given the above partition info and comms....
Note I have not provided any additional information to "dd" regarding global
cells as per the doxy notes so I assume it went away and computed it. I can't
figure out how to extract it however. I also have no idea how to modify each
local processor rgrid to include the ghost cells for that processor. Finally
given that info, I could exchange between processors to write to each local
processors ghost cells the corresponding "real" cell data from the neighbouring
meshes and continue the code.
Any help really appreciated!
Cheers,
Andy
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