This diagram illustrates the layout of the CGNS file, starting with the ZoneBC_t node, for an unstructured grid with boundary conditions defined at face centers.

The ZoneBC_t node has the following characteristics.

Below the ZoneBC_t node are the following three nodes defining the boundary conditions.

Below each of these BC_t nodes is a child node defining the elements over which the boundary condition acts. For the ilo boundary, this is:

For the ihi boundary, it's: And for the Walls boundaries, it's: