This information is also summarized in the documentation: *Units
<https://www.weewx.com/docs/5.1/reference/units/>*
On Wed, Oct 2, 2024 at 8:15 PM 'John Kline' via weewx-user <
weewx-user@googlegroups.com> wrote:
> IIRC,
>
> When your driver creates loop and archive observations, you need to set
> usUnits to reflect the correct system. For example, the vantage drive sets:
> 'usUnits': weewx.US
> In the loop data and archive records.
>
> If custom driver is in metric, set:
> ‘UsUnits’: weewx.METRIC
>
> If you do this, weewx will do the conversions and store values in the
> database in the system you specified when you created the database.
>
> But there is more. You have to use the correct metric units. To do this,
> see the weewx/units.py file. Look up the observation in that file, find
> the group, and then look up what that group expects.
>
> For example, rain is:
> "rain" : "group_rain",
>
> And, if you look up group_rain for metric, you’ll find group_rain is
> expecting cm:
> "group_rain" : "cm",
>
> # This dictionary maps unit groups to a standard unit type in the
> # metric unit system:
> MetricUnits = ListOfDicts({
> "group_altitude" : "meter",
> "group_amp" : "amp",
> "group_angle" : "degree_angle",
> "group_boolean" : "boolean",
> "group_concentration": "microgram_per_meter_cubed",
> "group_count" : "count",
> "group_data" : "byte",
> "group_db" : "dB",
> "group_degree_day" : "degree_C_day",
> "group_deltatime" : "second",
> "group_direction" : "degree_compass",
> "group_distance" : "km",
> "group_elapsed" : "second",
> "group_energy" : "watt_hour",
> "group_energy2" : "watt_second",
> "group_fraction" : "ppm",
> "group_frequency" : "hertz",
> "group_illuminance" : "lux",
> "group_interval" : "minute",
> "group_length" : "cm",
> "group_moisture" : "centibar",
> "group_percent" : "percent",
> "group_power" : "watt",
> "group_pressure" : "mbar",
> "group_pressurerate": "mbar_per_hour",
> "group_radiation" : "watt_per_meter_squared",
> "group_rain" : "cm",
> "group_rainrate" : "cm_per_hour",
> "group_speed" : "km_per_hour",
> "group_speed2" : "km_per_hour2",
> "group_temperature" : "degree_C",
> "group_time" : "unix_epoch",
> "group_uv" : "uv_index",
> "group_volt" : "volt",
> "group_volume" : "liter"
> })
>
>
> On Oct 2, 2024, at 7:51 PM, Thomas Carlin <thomascarl...@gmail.com> wrote:
>
> I have a sensor that is adding data to WeeWX with a custom driver.
> Unfortunately, the sensor provides values in various metric units, C, hPa,
> µg/m³, things like that. Obviously it is not a big deal to write these
> conversions into the driver, but i am curious if there is a prebuilt
> mechanism to convert them *before* they go into the database. Obviously,
> we can do the conversions after the fact, but logically it is better to
> convert and store everything in the same units.
>
> Do i need to do the conversions in the driver, or is there a way built
> into WeeWX?
>
> Many thanks!
>
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