Field Map: light -> illuminance

[alexdelprete]

I was having problems with the default mapping (with Influxdb and Grafana) and found the Field Map page in the wiki.

I found out, reading a couple of posts by Tom, that the field that better represents the light sensor should be in reality be "illuminance", introduced in weewx 4.2, and not luminosity.

https://github.com/weewx/weewx/issues/613#issuecomment-716136794 https://groups.google.com/g/weewx-user/c/gcjK6o_1QXE/m/qMMW3Mg_BwAJ

I used a [[field_map_extensions]] stanza, under [GW1000], to remap it:

[[field_map_extensions]]
     illuminance = light

With this I solved the issue I had exporting data to influxdb, but I thought it would be useful to have your opinion about the default mappings.

[gjr80]

You have stumbled onto an issue with a bit of history. Yes you are correct that the GW1000 field light is in fact illuminance and should be mapped to a field named illuminance. The problem is that before WeeWX v4.2.0 the wview_extended schema included a field luminosity but did not include a field luminance. WeeWX v4.2.0 included limited support for illuminance (this consisted largely of assigning luminance to the group_illuminance unit group) but never actually included illuminance in the wview_extended schema (or any other schema for that matter). Interestingly, while illuminance was assigned to a unit group, luminosity was not assigned to a unit group. Earlier this year Tom and I had some off-line discussions over these discrepancies when the weewx-user thread you linked was started. Essentially we had two choices; we could modify the wview_extended schema to include illuminance and maybe/maybe not remove luminosity with commensurate changes to the unit groups as well as GW1000 and fousb drivers. Alternatively, we could leave the wview_schema as is (ie luminosity but no luminance), fix the unit groups to be consistent and leave the GW1000 and fousb drivers as is.

Ultimately the decision was made (some months after WeeWX issue 613 was closed) to adopt the latter, leaving the wview_extended schema with luminosity but no illuminance accepting this was technically incorrect but avoiding a complicated upgrade procedure that would be required if there were changes to the wview_extended schema. If you look at the current (v4.5.1) wview_extended schema you will see it includes luminosity and has no illuminance.

One of the tasks that fell out of the decision to retain luminosity was to include some some suitable explanatory words in the WeeWX documentation. This was to be the cue for me to include some appropriate words in the GW1000 driver documentation, but it appears the WeeWX documentation was never updated. I will take this up with Tom.

In the end you have solved your issue in exactly the way it should, through altering your GW1000 driver field map.

[alexdelprete]

while illuminance was assigned to a unit group, luminosity was not assigned to a unit group.

that's what triggered my attention to the problem: when the influxdb driver creates the records, you can see fieldname_unit as the name of the record. But the luminosity record didn't have the _unit suffix. So I started investigating...

Question #1: why adding illuminance to the schema is such a breaking change? In the past the schema has actually been changed, IIRC.

Question #2: has luminosity been added to the unit group? Because in the last weewx version I still noticed that the influxdb driver exports the field without unit.

Gary, thanks a lot as always for the in-depth explanation, it really helps me understanding how things work with weewx, I appreciate it.