Plotting flag variables

[maxwelllevin]

Hi act-atmos team,

I'm working with some ARM data that has a state indicator variable I want to plot. In my case I am working with there is a cloud_phase variable which looks something like this:

cloud_phase(time, height):byte*
    long_name = Thermodynamic Cloud Phase
    units = 1
    flag_values:byte = 0, 1, 2, 3, 4, 5, 6, 7, 8
    flag_meanings = clear_sky liquid ice mixed_phase drizzle liquid_drizzle rain snow unknown
    missing_value:byte = -1
    _FillValue:byte = -1

So a value of 0 indicates clear sky, 1 indicates liquid, 2 indicates ice, etc. Note this is a bit different than QC variables because the value of cloud_phase will always match one of the flag_values or _FillValue exactly, whereas qc variables can match multiple flag_masks / bits to indicate a combination of different states. In other words the different states of the cloud_phase variable are mutually exclusive.

I want the plot to look something like this:

To the best of my knowledge, act doesn't quite do this yet (though it does do superbly with plotting qc variables). It would certainly be beneficial to me if the act.plotting module could be expanded to provide a method to plot mutually exclusive state indicator variables, so I wanted to float the idea to you all and see if you think it's worthwhile.

Reference

ARM Standards §6.5 discusses how ARM handles exclusive and inclusive state indicator variables:
https://www.arm.gov/publications/programdocs/doe-sc-arm-15-004.pdf

The CF Conventions also discuss variable flags here:
https://cfconventions.org/cf-conventions/cf-conventions.html#flags

[AdamTheisen]

@maxwellevin this is a great idea and I'm wondering if we can fit it in with the existing plotting with some discrete shading keywords. I'm going to create an issue from this and add it to the list.

[kenkehoe]

@maxwellevin what datastream did you use for your example plot?

[maxwelllevin]

It's thermocldphase, a new ARM vap that hasn't been released for evaluation yet (coming soon). I can point you to some data on the ARM server if you'd like to use part of it to test.

[kenkehoe]

I've created PR #480 for this feature request

.