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elevation defaults to -480m consistently

Martin
over 4 years ago

Hi.

I know the VA 4 has a basic altimeter that requires calibration, but does it not have any memory to use last calibration value before it calibrates?

If I don't always wait 30+seconds after GPS signal has been acquired, then my altitude at home will always be around -480m.

If I wait 30+ seconds, it's about 20m.

There is no progress bar or status to know if altimeter has been calibrated and if I accidentally start an exercise too early why can't it just use the value that was stored up to that point?

As an example, once calibrated, my watch face can show this value fairly accurately as would a altitude widget that reads the barometric altimeter. If I decide to go for a walk or run, and press start once GPS signal is good, the watch immediately sets the altimeter to around -480m. Very frustrating.

  • 0 over 4 years ago

    It can't remember the previous value, because it depends on the weather (pressure), which changes constantly.

  • 0 over 4 years ago in reply to ovekvam

    ?  I don't follow your reasoning. 
    Of course it could remember the value... other devices do, so why can't the VA4?

    After initiating an exercise that has allowed for a calibrated reading, a widget or clock face that accesses the altimeter will show the actual calibrated reading continuously ... changing obviously if I go up or down in elevation.

    My clock face can be showing around 28M above sea level all day long, and then when I choose to go for a walk, run or cycle, and start an activity after GPS shows ready, the reading goes to -480m or -485m or whatever it chooses that day. Why? it was roughly accurate before I started? And if I just happen to Start an exercise just shy of the calibration time, it all goes to shite.

    I understand that the altimeter needs constant calibration since weather pressure systems and temperature can cause it to drift from accurate. However, my EDGE 530 drifts too, and I could start a ride at say 43m elevation at start, and within a few seconds of starting gets set to the proper elevation of my home at around 23m. This is very evident on the elevation graph.

    There is no reason why the Garmin couldn't apply this to the Vivoactive 4. Its far less absurd to start with an existing slightly inaccurate reading and then calibrate that at the beginning of an exercise. At the very least Garmin should not state READY when it's not completely ready having also set the proper altitude.

  • +1 over 4 years ago in reply to ovekvam

    Well, seems I was correct in my presumption of how it should work.

    After a factory reset on Monday, everything works as I thought it should.

    1) GPS Calibration is needed, and this is achieved via waiting for a GPS signal and waiting at least 30 seconds. 
    Going back to a watch screen with a altimeter reading verifies this was done.

    2) starting a GPS activity now uses the current altimeter reading as a starting point, and this gets further calibrated in the first few seconds of the activity. If the initial altimeter reading (old calibration) has drifted then the beginning of an activity will see either a slight rise or fall in altitude as the altimeter gets calibrated again.

    No longer a -480 or 490m drop in elevation at a start of an activity even though the previous calibration was roughly correct still. 

  • 0 over 4 years ago in reply to Martin

    Some people exploit this altitude drift when making Strava segments. They switch on the watch and start it immediately on a flat, short stretch. If the altitude drifts up, the segment will appear as a steep climb.

    In my area in Norway, the VA4S altitude reading is permanently almost 100m too low, making most of my activities appear as they are below sea level, even when they never are. I am guessing Garmin has a bug in their geometric model of where the sea level is in our area. 

  • 0 over 4 years ago in reply to ovekvam

    People who exploit this are only lying to themselves... Joy No sympathy there.

    I understand that the accuracy of a GPS calibration can still be inaccurate. And in your case, it's calibrated inaccurately consistently. 
    How long have you waited post GPS lock on before starting an activity?
    My VA4, EDGE 530, and two iPhones in the household all show the an altitude reading within about 3M of each other. 

    My original problem was that an old calibration value wasn't carried forward into an activity, and that starting an activity would almost always start at -480m and most of the time never change either. The total elevation change during the activity would be roughly correct. It's only happened once where the activity recorded a start at -490 and then within a few seconds jump to 20m. 

    After the reset, my device behaves as it should. If I wait for a GPS signal and press start immediately, the elevation correction would be recorded into the activity as either a loss or gain in elevation. If I wait a little longer, like 10-20seconds after GPS signal has been acquired, the start of the activity will start with a corrected elevation already.

    Before, the correct elevation would only be recorded if I waited at least 30 seconds after GPS signal was acquired. Otherwise it would default to -480 or -490m

  • 0 over 4 years ago in reply to Martin

    I have tried to wait anything from 5 seconds to over 10 minutes. The altitude offset seems very consistent. The thing is that the earth is not a perfect sphere, so there are algorithms to determine where the sea level is in different locations. It seems like my watch is not doing this correctly in my area. 

    People who exploit the altitude drift are not only lying to themselvses, but also to others. When I search for climb segments in the area, some very flat segments show up in my search as steep climbs.

  • 0 over 4 years ago in reply to ovekvam

    I would have to verify, but Strava using one device's elevation gain data as absolute for a segment creation doesn't sound right... I though Strava uses map data to calculate the start and end elevation and grade of a segment.


    You can always report a segment if you suspect an issue. 

  • 0 over 4 years ago in reply to ovekvam

    Hmmm. Strange indeed. Probably worth reporting this as a serious oversight for Strava segment creation.

  • 0 over 4 years ago in reply to ovekvam

    Seems like this is done on purpose... how idiotic.

    https://support.strava.com/hc/en-us/articles/216919447-Elevation-for-Your-Activity

    If they have an elevation basemap I don't see why that isn't used as the source for a segment, especially if said basemap is cross referenced with elevation data from devices with barometric altimeters.