vtkHyperTreeGrid Paraview example in 2D

ParaView Support
12

The paraview example is indeed out of date, that will be updated.

There are 2 main ways you could create your htg.

  • You can do it “by hand”. Let me show an example in c++ (don’t forget to include relevant headers)
vtkNew<vtkHyperTreeGrid> htg;
/*
 * Initialize it like you did with x, y, and z coordinates
 */
vtkIdType treeOffset = 0;
for (vtkIdType i = 0; i < htg->GetCellDims()[0]; ++i)
{
  for (vtkIdType j = 0; j < htg->GetCellDims()[1]; ++j)
  {
     // We go through every trees in the grid. It is a 2D grid so there are 2 loop.
     // Let's initialize k = 0 for completeness.
    vtkIdType k = 0, treeId;
    // Get the tree index.
    htg->GetIndexFromLevelZeroCoordinates(treeId, i, j, k);
    // Create a cursor (there are many kinds, we can go through them later if you have questions)
    auto cursor = vtkSmartPointer<vtkHyperTreeGridNonOrientedCursor>::Take(
        htg->NewNonOrientedCursor(treeId, true /* create */);
    // Set tree indexing offset
    cursor->GetTree()->SetGlobalIndexStart(treeOffset);
    // You have to write your own procedure here, I assume you wrote the following
    // recursive function
    RecursivelySubdivideLeaves(cursor, paramsDrivingSubdivision);
    treeOffset += cursor->GetTree()->GetNumberOfVertices(); // we update the offset.
  }
}

Then, to subdivide a leave, you need to call cursor->SubdivideLeaf(). You have access of the global htg level index in the scalar fields with cursor->GetGlobalIndex(), and index relative to one tree with cursor->GetVertexId(). To navigate, you have cursor->GetNumberOfChildren() telling you how many children you have, cursor->ToChild(iChild) and cursor->ToParent() to walk inside the tree, and cursor->IsLeaf() to know when to stop.

  • You can also use vtkHyperTreeGridSource, which will create the structure of a htg given a descriptor. You can use it to create a htg pretty fast. The descriptor works as follow: . means “leaf”, R means subdivide, | means next level. An htg of 4 quadtrees like you showed in your first comment would be ..... If you want to subdivide the 4th tree, you would write ...R|..... If you want to subdivie the 2nd and the 4th tree, you would write .R.R|......... Finally, if you want to additionally subdivide the first child of the 4th tree, you would write .R.R|....R...|.....

Now, concerning writers, there might be a bug that went through the release. To make sure this works, you should call writer->SetDataSetMajorVersion(0) before your write. You don’t need to specify this parameter for the reader.

Did I answer your question or are there still some dark corners? Don’t hesitate to ask for clarification if something isn’t clear.

Thanks,
Yohann