Add units to the metadata file

[eldobbins]

We want to add some notation of units to the metadata.json file.

• units should be machine readable, so we need a standard
• the standard should include the derived units we need to express
• the standard should be acceptable to tools/languages that will want to read the data
  • Python and R
  • collaborators like Catalyst

Because we need to balance all these things, I made an issue.

Things to look at:

• UDUNITS2
  • https://cran.r-project.org/web/packages/units/vignettes/measurement_units_in_R.html says works in R
    • " udunits on the other hand is the units standard of choice by the climate science community, and is adopted by the CF (Climate and Forecast) conventions, which mostly uses NetCDF"
  • there are python language packages too
• pint
  • is python for sure but R = ??
  • used by Catalyst and Datacette. Well, maybe
• UCUM Unified Code for Units of Measure is maybe dead?
  • that R ref says "... links seem to be dead. UCUM is the preferred encoding for standards from the Open Geospatial Consortium"
• https://cf-xarray.readthedocs.io/en/latest/units.html extends pint to be like UDUNITS1
• frictionless can't decide and also this

[ianalexmac]

"units": have been added to metadata.json, which parse and show up on the table previews on the data page.

[eldobbins]

Closing this issue as complete. If we want to use a different standard later, we can switch.

PS. Added info from this card to the wiki to simplify coming back to it.