Hello @ChrisBarker-NOAA and all, After some very illuminating discussion over at https://urldefense.us/v3/__https://github.com/ugrid-conventions/ugrid-conventions/issues/52__;!!G2kpM7uM-TzIFchu!gsrPpUHyBO1L3RCLlnbI4ykGpE8GyFUQGCnBa97TVwjO6tJnc_z4tfusXiad6JE3NXdsbwwppNw$ , and some offline discussions, @JonathanGregory and I have come up with some suggested text to the data model in [Appendix I](https://urldefense.us/v3/__https://cfconventions.org/cf-conventions/cf-conventions.html*appendix-CF-data-model__;Iw!!G2kpM7uM-TzIFchu!gsrPpUHyBO1L3RCLlnbI4ykGpE8GyFUQGCnBa97TVwjO6tJnc_z4tfusXiad6JE3NXdsLhQqXgs$ ) that we hope will update the CF data model for the mythical connectivity.
The new text is hopefully self-explanatory and edits the "Domain construct" section of Appendix I (edits in italics) and provides a new section describing a new construct type - the "network topology construct". Here we are using "network topology" in [this sense](https://urldefense.us/v3/__https://en.wikipedia.org/wiki/Network_topology__;!!G2kpM7uM-TzIFchu!gsrPpUHyBO1L3RCLlnbI4ykGpE8GyFUQGCnBa97TVwjO6tJnc_z4tfusXiad6JE3NXdsctCuFWE$ ), but there may well be better names. Remember that the CF data model is a logical data model that is independent of the encoding, so it not a problem that the connectivity array does not look like a UGRID netCDF connectivity variable. (I took the liberty of rearranging some the network topology text after Jonathan last saw this - I take full responsibility for any negative consequences.) ---- ### Domain construct The domain construct (figure 3) describes a domain comprising measurement locations and cell properties. The domain construct is the only metadata construct that may also exist independently of a field construct. The domain construct contains properties to describe the domain (in the same sense as for the field construct) and relates the following metadata constructs * Domain axis constructs. * Dimension coordinate and auxiliary coordinate constructs. * Coordinate reference constructs. * Domain ancillary constructs. * Cell measure constructs. * _Network topology constructs._ All of the constructs contained by the domain construct are optional (as indicated by "0.." in figure 3). In CF-netCDF, domain information is stored either implicitly via data variable attributes (such as coordinates), or explicitly in a domain variable, _or a UGRID mesh topology variable. In the latter two cases_, the domain exists without reference to a data array. ### Network topology construct A network topology describes the connectivity of cells of domain indexed by a subset of the domain axis constructs. When two cells are connected, operations on the data stored on them may be assumed to be continuous across their common boundary. A network topology construct describes logically and explicitly the network topology of cells indexed by a single domain axis construct. A network topology construct contains a connectivity array that spans a unique domain axis construct with the addition of an extra dimension of the same size, such that each dimension indexes the cells. The array is symmetrical, and each element indicates whether the pair cells to which its indices refer are connected. A network topology that has no corresponding network topology construct, which includes those for multiple domain axis constructs, is nonetheless implicitly defined by a function of both the physical contiguousness of the cells, and the nature of the real world or simulated processes that produced the data. For example, in a field which contains both land and ocean cells, connections between land and ocean cells might be excluded for some physical processes.The description of such an implicit network topology may require metadata that is external to CF. In CF-netCDF a network topology can only be provided for a domain defined by a UGRID mesh topology variable. In this case, the connectivity array is supplied by a UGRID connectivity variable (such as a "face_face_connectivity" variable). -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://urldefense.us/v3/__https://github.com/cf-convention/cf-conventions/issues/153*issuecomment-880923765__;Iw!!G2kpM7uM-TzIFchu!gsrPpUHyBO1L3RCLlnbI4ykGpE8GyFUQGCnBa97TVwjO6tJnc_z4tfusXiad6JE3NXdsqqsaF5E$ This list forwards relevant notifications from Github. It is distinct from [email protected], although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to [email protected].
