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Appendix A: Mesh Topologies

The CF attributes listed here may be used to define mesh topologies ([mesh-topology-variables]). This list is intended as a summary of the attributes that have been standardized via the UGRID conventions [UGRID], which should be consulted for further details. UGRID attributes that are not currently recognised by the CF convensions are included in the list.

The "Type" values are S for string and I for integer. The "Use" values are MT for mesh topology variables, LIS for location index set variables, D for data variables, Do for domain variables, and Con for connectivity index variables.

Table K.1. Mesh topology attributes

Attribute	Type	Use	Description
boundary_node_connectivity	S	MT	Specifies an index variable identifying the nodes that define where boundary condtions have been provided. Not currently recognised by the CF conventions.
cf_role	S	MT, LIS	Specifies the roles of mesh topology or location index set variables.
coordinates	S	LIS	Specifies the auxiliary coordinate variables associated with the characteristic locations of the subset of mesh topology locations.
edge_coordinates	S	MT	Specifies the auxiliary coordinate variables associated with the characteristic location of the edges (commonly the midpoint).
edge_dimension	S	MT	Specifies the dimension used to index the nodes in the edge connectivity variable.
edge_face_connectivity	S	MT	Specifies an index variable identifying all faces that share the same edge, i.e. are neighbours to an edge.
edge_node_connectivity	S	MT	Specifies an index variable identifying for every edge the indices of its begin and end nodes.
face_coordinates	S	MT	Specifies the auxiliary coordinate variables associated with the characteristic location of faces.
face_dimension	S	MT	Specifies the dimension used to index the edges in the face connectivity variable.
face_edge_connectivity	S	MT	Specifies an index variable identifying for every face the indices of its edges.
face_face_connectivity	S	MT	Specifies an index variable identifying all faces that share an edge with each face, i.e. are neighbours.
face_node_connectivity	S	MT	Specifies an index variable identifying for every face the indices of its corner nodes.
location	S	D, Do, LIS	Specifies the location within the mesh topology at which the variable is defined.
location_index_set	S	D, Do	Specifies a variable that defines the subset of locations of a mesh topology at which the variable is defined.
mesh	S	D, Do, LIS	Specifies a variable that defines a mesh topology.
node_coordinates	S	MT	Specifies the auxiliary coordinate variables representing the node locations (latitude, longitude, or other spatial coordinates, and optional elevation or other coordinates).
start_index	I	LIS, Con	Indicates whether 0- or 1-based indexing is used to identify connected geometric elements; connectivity indices are 0-based by default.
topology_dimension	I	MT	Indicates the highest dimensionality of the geometric elements.
volume_coordinates	S	MT	Specifies the auxiliary coordinate variables associated with the characteristic location of volumes. Not currently recognised by the CF conventions.
volume_dimension	S	MT	Specifies the dimension used to index the faces in the volume connectivity variable. Not currently recognised by the CF conventions.
volume_edge_connectivity	S	MT	Specifies an index variable identifying for every volume the indices of its edges.
volume_face_connectivity	S	MT	Specifies an index variable identifying for every volume the indices of its faces. Not currently recognised by the CF conventions.
volume_node_connectivity	S	MT	Specifies an index variable identifying for every volume the indices of its corner nodes. Not currently recognised by the CF conventions.
volume_shape_type	S	MT	Specifies a flag variable that specifies for every volume its shape. Not currently recognised by the CF conventions.
volume_volume_connectivity	S	MT	Specifies an index variable identifying all volumes that share a face with each volume, i.e. are neighbours. Not currently recognised by the CF conventions.