It is probably not much of an issue for you at 364 ft of elevation. But stations at greater elevation like the OP at 4400 ft, that do not receive station pressure data from the console will have a more difficult time properly calculating Altimeter pressure since their consoles only provide sea level pressure. Calculating Altimeter by way of Sea Level pressure is convoluted and adds yet another factor of data accuracy problem. Calculating Altimeter pressure is enough of a issue already for stations at high elevation to then also need to contend with figuring out what station pressure is if it is not provided....that is two strikes against the best data possible. You can't do anything about your high elevation but if you could actually have the most precise station pressure it would help.
On Tuesday, January 12, 2021 at 5:07:23 PM UTC-5 vince wrote: > Thanks for the summary (it helps), but I'm missing what actual problem > this thread is trying to solve. > > I've had my VP2 since jan'2009 and have ancient firmware on it. I've run > weewx for many years with the Vantage driver, doing nothing special to > tweak what it generates nor how. I've fed CWOP equally for many years > 'with' that data. CWOP has always been happy with the data as far as I > know. > > If I look at my data from CWOP online ( > https://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=C6881) it > looks like they have my actual and corrected pressures there. So is there > a problem ? > > On Tuesday, January 12, 2021 at 1:55:18 PM UTC-8 galfert wrote: > >> For anyone confused or not able to follow along....here is the premise of >> what Gary and I are discussing. >> >> Davis LOOP1 data in terms of barometric pressure only sends corrected sea >> level pressure. >> Davis LOOP2 data in terms of barometric pressure only sends station >> pressure (atmospheric pressure). >> >> CWOP requires Altimeter pressure which needs to be calculated. The best >> way to calculate Altimeter is to have station pressure (atmospheric) that >> you only get from LOOP2. If LOOP2 is not available (not turn on or using >> old firmware) then the station will only send sea level pressure to WeeWX. >> This will then require WeeWX to back track and try and figure out what >> station pressure is ...and then use that value to then calculate Altimeter >> and that is not very accurate of a process. You can't send LOOP1 sea level >> to CWOP...not the same. >> >> >> On Tuesday, January 12, 2021 at 4:49:05 PM UTC-5 galfert wrote: >> >>> Well then this seems to be a big limitation for any Davis station that >>> is not using a WLL! Seems like the WLL is a better solution than other >>> loggers and then ending up with a mess of combined calculated and received >>> values for barometric pressure. Unless it is possible to set things so that >>> Altimeter is only calculated during LOOP2 reads, and to only accept sea >>> level during LOOP1. I'm not sure if that makes sense or if it is even >>> possible, nor what ramifications messing with all this entails nor what the >>> other undesired results may be. >>> >>> Bottom line....seems like WLL is a better way to get complete live data >>> from the station. >>> >>> On Tuesday, January 12, 2021 at 4:36:03 PM UTC-5 gjr80 wrote: >>> >>>> I have no WLL experience so short answer is I don’t know. >>>> >>>> But the loop_request setting is a vantage driver setting, as far as I >>>> know you need to use a different driver for WLL. Also, there are a number >>>> of WLL drivers; looking at one just now I see it appears to emit pressure >>>> and altimeter, though as I said I don’t know enough about WLL to draw any >>>> conclusions. >>>> >>>> Gary >>>> On Wednesday, 13 January 2021 at 07:22:28 UTC+10 galfert wrote: >>>> >>>>> Gary, >>>>> That is very interesting and possibly important information. Is what >>>>> you mention dependent on the type of logger used? Meaning is the data >>>>> switching (LOOP1 / LOOP2) still an issue with the WLL? >>>>> >>>>> >>>>> On Tuesday, January 12, 2021 at 4:14:00 PM UTC-5 gjr80 wrote: >>>>> >>>>>> Assuming can be a dangerous business! If you have not specified >>>>>> anything for loop_request then you will be using LOOP1 only (the >>>>>> default), >>>>>> whether that is the ‘best available format’ depends on your >>>>>> circumstances I >>>>>> guess. Should you happen to specify loop_request = 3 in order to get the >>>>>> best of both worlds (by alternating between LOOP1 and LOOP2 packets) be >>>>>> aware that this can cause WeeWX loop packets to alternate between >>>>>> hardware >>>>>> provided and software calculated values for station pressure and >>>>>> altimeter >>>>>> (and archive records will then have a blend of both). If you do use >>>>>> loop_request I suggest you carefully read the loop_request stanza >>>>>> <http://weewx.com/docs/usersguide.htm#%5BVantage%5D> in the User’s >>>>>> Guide. >>>>>> >>>>>> Gary >>>>>> >>>>>> >>>>>> On Wednesday, 13 January 2021 at 06:12:20 UTC+10 n0...@n0nb.us wrote: >>>>>> >>>>>>> >>>>>>> > If you don't have the latest firmware then you may not have Loop2 >>>>>>> data. Not >>>>>>> > having Loop2 data will inhibit greater Altimeter calculation by >>>>>>> WeeWX >>>>>>> > because station pressure will be missing and it will have to work >>>>>>> backwards >>>>>>> > and that is less accurate. Better to send the software station >>>>>>> pressure >>>>>>> > which is done by having Loop2 data. >>>>>>> >>>>>>> According to the Davis site the latest firmward for the Vantage Pro2 >>>>>>> is >>>>>>> 3.15 and wee_device reports my console is at 3.15. I have not >>>>>>> specified >>>>>>> which LOOP data WeeWX is to use as I assume it is coded to use the >>>>>>> best >>>>>>> available format. >>>>>>> >>>>>> -- 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/9b3583dd-9187-4d06-a96a-e6f3aed84ec6n%40googlegroups.com.
