Using ParameterGroup to annotate ancillary data (such as quality flags) of a variable

[PaulVanSchayck]

We've been considering the use of ParameterGroup to annotate quality flag variables which are directly associated to, for example, observational variables. In the CF conventions this is referred to as ancillary data.

The spec also uses an example with mean values and an associated stddev. So this seems to indicate that the intended use of ParameterGroups can be the same as the ancillary data that the CF conventions describe.

What's missing from the current specification is to indicate which variable of a ParameterGroup is the primary variable and which are the supporting ('ancillary') variables. What are your thoughts on this? Would it help to define this somehow in a ParameterGroup? For example by defining that the first member of a group is the primary variable. Another option would be to do this similarly as the CF conventions and add an attribute ancillaryVariables: list[str] to Parameter.

I've commented on an existing and related issue opengeospatial/ogcapi-environmental-data-retrieval#634 (comment) in the EDR spec which talks about how ParameterGroup can be used in EDR.

[chris-little]

@PaulVanSchayck I've added this to the discusssion topics for next week's meeting of the EDR API SWG in Boulder. I think this would be a CoverageJSON V1.1 topic and an API-EDR Part 1: Core V1.3 and/or Part 4: Aggregation and Summary Statistics topic for next year.

@jonblower FYI

[jonblower]

@PaulVanSchayck @chris-little Yes, this is a good topic for discussion. The description of ParameterGroups in the CovJSON spec is not really complete and this would be a good use case to nail down.

[chris-little]

@PaulVanSchayck @jonblower I now think that there are 4 separate uses:
EDR Part 4 Aggregation and Statistics ? ParameterGroups (also in CoverageJSON)

1. Group vector and tensor scalars together (e.g. wind, currents, wind and wave stresses)
2. Associated stats – value plus Std, Mean, Median, Mode, Quartiles, etc
3. Associated Q/C flags
4. Convenient but arbitrary group of parameters (e.g. p, T, u, v, q)