UGRID compliance#

Mesh topologies are produced by the mesh generators following the UGRID convention [1]. The convention specifies mandatory and optional data. The following sections document variables/data which are output for a given mesh topology in a mesh output file:

  • UGRID mandatory data

  • UGRID optional data

  • Non-UGRID data for application support

Mandatory UGRID data#

  • node_coordinates
    Node coordinates, [lon,lat] for spherical domains, [x,y] for
    flat cartesian domains.
  • face_node_connectivity
    Integer identifiers of nodes that construct a given face.

Optional UGRID data#

  • face_coordinates
    These are derived from the node coordinates as follows:

    • For Cubed-Sphere meshes, the faces are not necessarily of similar size along the [lon,lat] axes.

      1. For the nodes connected to a given face, the node coordinates are converted from (lon, lat, radius=1) to cartesian [x,y,z] coordinates.

      2. The face centre is calculated as the mean of vector sum of the node coordinates, allowing for a radius ratio.

      3. The face centre coordinates are converted back to (lon, lat).

    • For Planar meshes, the domains are constructed to be aligned with the coordinate axes, whether [lon,lat] or [x,y]. The face centre coordinates are obtained from an offset to the cell’s NW node location., i.e. (x,y) NW node + 0.5(\(\Delta\) x, \(-\Delta\) y) cell.

  • edge_node_connectivity
    Integer identifiers of nodes that construct a given edge.
  • face_face_connectivity
    Integer identifiers of faces adjacent to a given face.
  • face_edge_connectivity
    Integer identifiers of edges that construct a given face.

Non-UGRID data#

  • Geometry
    Indicates the geometrical shape the mesh domain forms, i.e. spherical.
    Related attribute: geometry
  • Coordinate system
    Indicates the coordianate system used to interpret coordinate values.
    Related attributes: coord_sys
  • Periodicity
    Indicates the periodic state of the domain boundaries on a given axis.
    Related attribute: topology, periodic_x, periodic_y
  • InterMesh maps
    Indicates the targets of InterMesh maps that are present in the file, where the given mesh is the source.
    Related attributes: n_mesh_maps, maps_to
  • Domain extents
    Domain extents along the coordinate system axes.
    Related attributes: domain_extents
  • Domain feature locations
    Coordinate locations of significant features on the mesh, e.g. North pole.
    Related attributes: north_pole, null_island, equatorial_latitude

Footnotes