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: