And this document explains why GPS altitude sucks (to be polite!): http://www.montereysar.org/SARMembersDocs/UsingaGarminGPSwithPaperLandMaps_Manual.pdf
Regards, Garry Lockyer C: +1.250.689.0686 E: [email protected] > On Jan 10, 2021, at 18:05, Brent Dowell <[email protected]> wrote: > > > Thanks again! > >> On Sunday, January 10, 2021 at 6:02:00 PM UTC-8 [email protected] wrote: >> The note Derived variables from Davis has a pretty good discussion of this. >> >>> On Sun, Jan 10, 2021 at 5:38 PM Brent Dowell <[email protected]> wrote: >>> Correct Altitude is entered. >>> >>> I'm getting an average error of 3.5 millibars. >>> >>> My altitude is pretty close to the local airport, and I used a fairly calm >>> day to adjust my barometer to match that. Our altitude is also relatively >>> close, i.e. the airport is 4403ft and I'm at 4410. Althought that 4410 >>> could be off, I had used that for my altitude for years. >>> >>> Took another reading via gps today and have adjusted that to 4293, which >>> seems like it could be a significant differences. >>> >>> Thanks so much for your help in getting me to understand it. I've managed >>> to learn to ignore the wind errors, as I live on a hillside and don't see >>> anyway my wind data will ever match. if I need to do that for barometer, >>> I'll work on it. lol. >>> >>> Would just like to figure out what I'm doing wrong. >>> >>> >>> >>> >>> 1. That you have a Vantage console; >>> Vantage Vue Console >>> 2. That you are using regular LOOP packets, not the newer LOOP2 packets; >>> loop_request = 1 >>> 3. That you are using hardware record generation. >>> prefer_hardware >>> >>> From the wee_device command. >>> >>> BAROMETER CALIBRATION DATA: >>> Current barometer reading: 30.222 inHg >>> Altitude: 4293 feet >>> Dew point: 24 F >>> Virtual temperature: 32 F >>> Humidity correction factor: 1.1 >>> Correction ratio: 1.175 >>> Correction constant: +0.000 inHg >>> Gain: 0.000 >>> Offset: -16.000 >>> >>> >>>> On Sunday, January 10, 2021 at 5:01:53 PM UTC-8 [email protected] wrote: >>>> I'm assuming: >>>> >>>> 1. That you have a Vantage console; >>>> 2. That you are using regular LOOP packets, not the newer LOOP2 packets; >>>> 3. That you are using hardware record generation. >>>> >>>> If all this is true, then what's happening is that WeeWX is downloading >>>> altitude and temperature corrected barometric data (what pilots call QFF) >>>> from the console. However, CWOP wants pressure corrected only for altitude >>>> (not temperature; pilots call this QNH). So, WeeWX uses an algorithm to >>>> calculate that. This is then what is uploaded. >>>> >>>> First thing is to make sure you have the correct altitude entered in your >>>> console. You will also want to know whether the console is applying any >>>> barometric corrections. Both can be checked using the utility wee_device, >>>> with the --info command. >>>> >>>> wee_device --info >>>> >>>> This will tell you what altitude your console thinks it's at, as well as >>>> any barometric calibration data. >>>> >>>> -tk >>>> >>>> >>>> >>>>> On Sun, Jan 10, 2021 at 4:24 PM Brent Dowell <[email protected]> wrote: >>>>> I've been chasing my tail a bit trying to get my data that I upload to >>>>> CWOP to pass the madis checks, which, from what I've read is a bit >>>>> problematic. >>>>> >>>>> My question though is what should I have my console set as far as >>>>> altitude and barometer reduction. Right now I have it set for my correct >>>>> altitude and am using the altimeter setting. My readings are consistently >>>>> 'low' compared to the madis QC Check. >>>>> >>>>> It looks like to me that the values being uploaded are in fact low (raw >>>>> aprs data) and do not match whats on my console. So it appears that >>>>> weewx must be doing some altimeter calculation on my data and is sending >>>>> that on to cwop? I'm wondering if I'm missing a setting somewhere in my >>>>> weewx config to accout for that? >>>>> >>>>> Some of the research I've done on the issue talks about davis being a bit >>>>> of a pain because they out put the altimeter corrected data already and >>>>> that setting altitude to 0 and using the altimeter reduction fixes it? >>>>> >>>>> Sorry about dredging up an old issue, but I couldn't find much recent >>>>> information on this. >>>>> >>>>> Thanks in advance for any help. >>>> >>>>> -- >>>>> 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 [email protected]. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/weewx-user/d425ef32-4da0-49e1-b2d4-fd21dffdfbaen%40googlegroups.com. >>> >>> -- >>> 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 [email protected]. >> >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/weewx-user/49100cc7-7e2f-478f-9065-f0f42a92db3bn%40googlegroups.com. > > -- > 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 [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/9c6cfc66-af04-4813-83cc-8fc021e39074n%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "weewx-user" group. 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