Sounds like a perfect job for the xtypes system. See this wiki article: *WeeWX V4 user defined types (xtypes)* <https://github.com/weewx/weewx/wiki/WeeWX-V4-user-defined-types>. See if it answers your question.
If you define a derived variable using xtypes, it becomes a first-class type and can be used in plots, or tagged expressions. If it appears in your database schema, it will also be put in the database. -tk On Fri, May 22, 2020 at 7:14 AM Maarten van der Hoeven <hoeve...@gmail.com> wrote: > Hi group, > > Running weewx 4, Python 3, Mysql-database, Vantage Pro 2 with solar, UV. > > Within Weewx, I want to calculate a derived value from two existing values > that's provided by my weather station. To be more specific, in the > Netherlands, the shortage of precipitation is calculated by the amount of > rainfall minus the amount of evapotransipration (sum of max ET-values every > day). During the period of april till september, it;'s a drought indicator. > > My SQL-query to do show is, where 'tekort' (Dutch) stands for 'shortage'. > > select abs(round(sum(archive_day_rain.sum)-sum(archive_day_ET.sum),0)) as > tekort from archive_day_ET,archive_day_rain where > from_unixtime(archive_day_rain.datetime,'%Y')=year(curdate()) and > month(from_unixtime(archive_day_rain.datetime)) >= 4 and > month(from_unixtime(archive_day_rain.datetime)) <= 9 and > archive_day_rain.datetime=archive_day_ET.datetime; > > What I am doing right now, is running a crontab job, and start my > PHP-script every minute to calculate the outcome of the SQL-script above > and writes the outcome to a plan txt-file. Next step is to grab this value > from the txt-file and show it (javascript) on my website. See > http://www.weerinwelsum.nl, below the webcam. It says ' Doorlopend > neerslagtekort', [amount of millimeters]. This is the value I am talking > about. > > What I really want to achieve, is that I calculate this derived valu by > WeeWX itself, and make this derived value available for everything that's > wants to use is. For example, store this derived value in a database-field > I am not using (for example, soilTemp4) and make this derived value > available for whatever skin (in my case, Belchertown). In other words, > Weewx calculates this new value and makes it available for the complete > WeeWX-ecosystem (if you understand what I mean). > > Am I clear in what I want to achieve? And is this possible, and what are > the pointers to do so? > > -- > You received this message because you are subscribed to the Google Groups > "weewx-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to weewx-user+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/d48cfc39-5e17-4795-a75f-ac4c266e73b0%40googlegroups.com > <https://groups.google.com/d/msgid/weewx-user/d48cfc39-5e17-4795-a75f-ac4c266e73b0%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/CAPq0zEAAbYg%2BVYa-3oe_j-43z3fP0Sn6h9oyaaimcydcMFLdbg%40mail.gmail.com.
