Parallel Stitching and Ghost Cells

When visualizing partitioned unstructured grids, ParaView treats each VTKHDF partition as a separate piece of geometry. To produce a seamless visualization and ensure mathematical correctness across the global domain, specifically named mesh-centered arrays may be written to the file. When ParaView encounters these arrays, it interprets them as metadata rather than ordinary point or cell data. These arrays are written using the standard point and cell data procedures.

• "vtkGhostType": an int8 cell-centered array identifying each cell as either a real cell owned by the local rank (value 0) or a ghost (duplicate) cell (value 1). This prevents duplicate cells from being rendered as overlapping geometry. While not required, ghost cells provide the context needed for filters to interpolate values across partition boundaries.

• "vtkGlobalPointIds": an int64 point-centered array providing a unique global index for every node. This prevents visual “cracks” in filters such as Contour or Slice.

• "vtkGlobalCellIds": an int64 cell-centered array providing a unique global index for every cell. This is required for accurate data integration (e.g., the Integrate Variables filter), ensuring that ghost or duplicate cells are not double-counted.