Thinking about this further, I said:

So would the answer be to have weewx-mqtt transmit in METRICWX and then 
> specify in the skin options group_wind = km_per_hour? Or would that cause 
> some miscalculations of wind data?


This would be invalid because the base skin would probably do the 
conversion, but the MQTT published message would have wind in m/s since the 
weewx-mqtt is setup for METRICWX (in this example). So no matter what I 
would display that observation as the published m/s but with a label of 
km/h on the page. 

I think I keep going back to the idea of having the weewx-mqtt 
<https://github.com/weewx/weewx/wiki/mqtt> send specific observations in 
the unit the user wants. Similar to a skin's [[[Units]]] [[[[Groups]]]] 
setup.


On Tuesday, November 20, 2018 at 9:57:20 PM UTC-5, Pat wrote:
>
> The Belchertown skin extension allows users to specify which group units 
> they want (much like the standard skin). I think this Issue on my GitHub 
> repo 
> <https://github.com/poblabs/weewx-belchertown/issues/23#issuecomment-440477408>
>  (which 
> Colin started) tries to a) get my own head wrapped around this and b) 
> suggest that the weewx-mqtt extension have the ability to also send 
> specific observations in the unit they want. Similar to a skin setup. 
>
> The MQTT extension can specify which units to transmit values in - but 
> it's an all or nothing conversion (US, METRIC, METRICWX). However based on 
> the table in the GitHub link (also attached here), I think what's trying to 
> be determined is if a hybrid scenario can exist somehow? Is that up to the 
> skin or up to the MQTT extension's transmit values?
>
> So would the answer be to have weewx-mqtt transmit in METRICWX and then 
> specify in the skin options group_wind = km_per_hour? Or would that cause 
> some miscalculations of wind data?
>
> An additional layer on top of all of this is that my skin just displays 
> what's present in MQTT. So if MQTT is sending dayRain_cm, I display that 
> even if the user wants dayRain_mm. So I think it would make sense for the 
> mqtt extension to be able to have granular ability on altering certain 
> observations. Otherwise the live-updated data coming from MQTT would have 
> to do in-situ conversions within the JavaScript functions (outside of weewx 
> conversion utilities) - which is another layer of complexity I'd like to 
> avoid if possible. 
>
> Lastly, if I'm not mistaken I think Colin's database is in US units based 
> on previous conversations we've had. 
>
> On Tuesday, November 20, 2018 at 8:23:05 PM UTC-5, gjr80 wrote:
>>
>> Colin,
>>
>> US, METRIC or METRICWX merely defines the units used in the weeWX 
>> database, it really should have no bearing on the presentation of data. For 
>> example, in the weeWX Standard skin (and for that matter other skins that 
>> simply use the weeWX report system for generating reports) the weeWX tag 
>> system and config settings in skin.conf/weewx.conf determine what 
>> presentation units are used. The user can freely (and simply) change these 
>> settings to display whatever units he/she requires in the resulting 
>> reports. Of course once you step outside extensions that only use the weeWX 
>> reporting system things become a little more complex, chnaces are you 
>> cannot rely solely on the weeWX tag system. In my view it really behoves 
>> those that produce extensions to weeWX to provide a means of selecting the 
>> units displayed by their extension, this may be as simple as the tags and 
>> skin/weewx config as previously mentioned, or for more complex extensions 
>> that say use MQTT or some other external app/system then some other 
>> mechanism is required. I am not fully across Pat's Belchertown extension 
>> but given it is still relatively young and being actively developed I would 
>> hope Pat would include some sort of user selectable settings/config options 
>> that allow you to display in whatever units you wish irrespective of the 
>> underlying database units.
>>
>> In getting back to your original question I suspect there is not too much 
>> that can be done by you to change things unless the Belchertown extension 
>> has some as yet unknown config settings to do what you want. Pat or other 
>> Belchertown users are the best placed to help with this. I also suspect 
>> there is little you can do directly to weeWX. If it was me I would be using 
>> US customary units in my database unless you have good reason not to (* see 
>> note) and I would be approaching Pat for a means to allow the user to alter 
>> the Belcherton presentation units.
>>
>> Note: FWIW I am in Australia and prefer to be able to view metric data on 
>> the odd occasion I want to look at my raw database data so I run METRIC 
>> (when I first started using weeWX there was only US or METRIC, METRICWX 
>> came later), I just have to keep reminding myself that rain is in cm. I 
>> also do all my development work using a US units database and since I 
>> mostly develop for my requirements that way I am forced to make sure I have 
>> a mechanism to display metric units.
>>
>> Gary
>>
>> On Wednesday, 21 November 2018 10:06:16 UTC+10, Colin Larsen wrote:
>>>
>>> Hi all
>>>
>>> I'm putting this out on the Weewx forum as I'm not sure if there is a 
>>> simple answer within Weewx for this problem.
>>>
>>> Down in NZ it is common to report rain in mm and wind speed in kp/hr
>>>
>>> In publishing MQTT data for Pats Belchertown skin this is causing an 
>>> issue whereby if I set MQTT to publish Metric I get wind speed and gust in 
>>> kp/h ..... but rain is reported in CM. Pats skin looks at the group units 
>>> which I have set to mm for rain and publishes the data, which is CM as he 
>>> sees the MQTT data is Metric and I get 0.14 mm of rain instead of the 1.4mm 
>>> it should be. Same for rain rate of course.
>>>
>>> I can fix the rain by using Metricwx which publishes rain in mm - but 
>>> then wind is in m/s so that reports wrong as the group units are kph.
>>>
>>> Can anyone suggest a solution within Weewx to the conundrum?
>>>
>>> Many thanks
>>> Colin
>>>
>>

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