Clarification of GridLocation for 2D Abutting Interfaces in SIDS

[brtnfld]

SIDS Section 8.4 Note No. 4 explicitly limits Abutting connections to Vertex or FaceCenter.

• In a strict topological sense, CGNS sometimes defines a "Face" generically as the (d−1) dimensional boundary entity.
• However, EdgeCenter exists as a valid enum in the library.
• For a 2D mesh (CellDim=2), forcing a user to label an edge connection as FaceCenter is confusing and semantically incorrect.

The Fix Needed in SIDS:

The documentation should be updated to explicitly state what is already implicitly accepted by the community (and the library ‡):

• Current: "For Abutting or Abutting1to1 interfaces, GridLocation can be either Vertex or FaceCenter."
• Proposed: "For Abutting or Abutting1to1 interfaces, GridLocation can be Vertex, or the center of the boundary element (EdgeCenter for 2D, FaceCenter for 3D)."

‡ See Discussion CGNS/CGNS#929

• Requires Steering Committee approval
• Check for other instances of 3D-centric assumptions in the SIDS