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why using a barometric altimeter...

afarnedi
over 6 years ago
just trying to find myself an answer but without success. Why implementing a barometric altimeter in a running (triathlon) sport watch? Is a matter of fact that barometric altimeter is not as precise as a gps altimeter so why Garmin did use for top level sport watch this solution? Every day, several time per day I recalibrate my altimeter; I never wake up in the morning having the right measure and every night I recalibrate it to my known home altitude (51 m) and when I do it using the GPS I never have the same result and I need to manually enter these 51m and few seconds after it's already signing a different altitude (+/- 2 meters). As far as I remember my "old" 735 XT very seldom needed a recalibration..it was so accurate comparing to 935 that from time to time I regret I've sold it...
So, why? to whom the barometer is useful for some reason? I can live without barometer as I think the 99% of the runners out there....who cares of atmospheric pressure when you go out for a run or a ride or even a swim? it probably means something if you use parachute or you climb mountains...but the "Forerunner" series are made "For-runners" mainly and I'm sure we can barely find a runner interested in barometer...especially if this is affecting also altimeter measure or elevation gain...my suggestion for Garmin is to let the users choose whether using barometer or not
sorry for the outburst
Andrea
  • 0 over 6 years ago
    >>as a matter of fact that barometric altimeter is not as precise as a gps altimeter
    I couldn't read beyond this point as I fell off my chair from laughter.
  • 0 over 6 years ago
    >>as a matter of fact that barometric altimeter is not as precise as a gps altimeter
    I couldn't read beyond this point as I fell off my chair from laughter.


    ok, that's probably my conclusion but reading around different threads barometric altimeter is more accurate only if you're able to calibrate pressure and altitude in a proper way and very often..otherwise it can be way too misleading and imprecise affected by too many factors like, weather, temperature, wind in the sensor etc etc..
    please try to sit again in your chair and read the rest of my post and, if needed, correct me where I'm wrong...
  • 0 over 6 years ago
    Andrea,

    if you want accuracy in elevation gain then GPS is by far not as accurate as altimeter.
    For the absolute height GPS is the way to go, as altimeter drifts slowly away due to pressure change.
    But for elevation gain or loss in an activity GPS doesn't get even close to altimeter.
    If you have for example a GPS accuracy of +-10m in heigth, then every second the watch will record a height in that range.
    +-10m seems to be very accurate but over a couple of kilometers this will add up quite significantly.
    Even with filtering you will not get accurate results as the watch doesn't know whether you are going up, down or stay on same altidute.
    Barometric doesn't have those issues.
    So way to go is barometric measurement with automatic calibration using GPS.
    Otherwise the data may be off by > 20-30%
  • 0 over 6 years ago
    One more thing.
    GPS is only enabled in an acitvity.
    So outside of activities you wouldn't get the altitude at all.
    Barometer still enables the watch the predicted altitude.
    Identifying whether the barometric preasure change outside activities is due to altitude or real preasure change is quite complex algorythmus and will not work 100% accurate.
  • 0 over 6 years ago
    When you go on a run or a bike trip, the absolute value of the altitude is usually not a very important information. What matters is the size of the small variations up and down when you run up or down a slope.

    It is well-known that a barometric altimeter is more precise than a GPS for this kind of information. So this is why barometric altimeters are used in sports watches.

    There are special cases, for example a continuous uphill bike trip up a hill with several hundred meter of ascent, where a GPS would probably be more precise for measuring the total variation. But in more normal situations, the barometric altimeter clearly beats the GPS.
  • 0 over 6 years ago
    Andrea,

    if you want accuracy in elevation gain then GPS is by far not as accurate as altimeter.
    For the absolute height GPS is the way to go, as altimeter drifts slowly away due to pressure change.
    But for elevation gain or loss in an activity GPS doesn't get even close to altimeter.
    If you have for example a GPS accuracy of +-10m in heigth, then every second the watch will record a height in that range.
    +-10m seems to be very accurate but over a couple of kilometers this will add up quite significantly.
    Even with filtering you will not get accurate results as the watch doesn't know whether you are going up, down or stay on same altidute.
    Barometric doesn't have those issues.
    So way to go is barometric measurement with automatic calibration using GPS.
    Otherwise the data may be off by > 20-30%


    Ok, that's an answer and I appreciate it and it clarifies a little bit the way of measuring height and elevation gain using the 2 different systems; one thing, when you say "automatic calibration using GPS" you mean in the altimeter menu to activate the auto calibration, right? this should report a better combination of accurate elevation gain and precise absolute height?
    The thing I don't understand is why Garmin do not provide the option of choosing what system to use. For example if I need to have a stable and reliable absolute height the 935 is not the right choice.
  • 0 over 6 years ago
    There are special cases, for example a continuous uphill bike trip up a hill with several hundred meter of ascent, where a GPS would probably be more precise for measuring the total variation. But in more normal situations, the barometric altimeter clearly beats the GPS.


    that's most of the time what's happening to me...I run and I ride MTB and most of the time I have ascents (or descents) of 300/400 meters and I always need to correct the elevation gain via web. Don't know if 300/400 meters are already too many for the altimeter being accurate but in my case they are.
  • 0 over 6 years ago
    Exactly, at the beginning of the activity GPS is used to calibrate altimeter.
    The 935 is very configurable and one of the available datafields is "GPS based altitude"(Or similar, as I have the German language used).
    You can configure every page with the values you would like to see.
    935 is for sure a good choice for almost all activities and you barely find anything better.
    Whether you need all of the functions or not is something different.
  • 0 over 6 years ago
    Exactly, at the beginning of the activity GPS is used to calibrate altimeter.
    The 935 is very configurable and one of the available datafields is "GPS based altitude"


    never seen before! that can be useful sometime.
    BTW, I'm not saying 935 is not a good watch...I owned all the FR series from 220 up to 935 going through the 225, 230 235 735 and 935 is by far the best I've ever had but the first with barometric altimeter and I've found some inaccuracies that made me wonder about the goodness of the barometric measurement
  • 0 over 6 years ago
    that's most of the time what's happening to me...I run and I ride MTB and most of the time I have ascents (or descents) of 300/400 meters and I always need to correct the elevation gain via web. Don't know if 300/400 meters are already too many for the altimeter being accurate but in my case they are.


    In my view, apart from absolute altitude at beginning and end, altimeter based measurement is the way to go for you.
    Do you happen to have a friend with GPS only watch?
    Pick a track where you have continous up or down for longer time.
    Take altitude at beginning and end and calculate delta.
    Your watch should be closer to real heigth difference, then your friends one.

    To just manage what to expect: if you ran the same track in the past using the 735 then you should see there is quite a difference.
    To measure your effort the elevation gain/loss are more relevant than the absolute height.
    So trying to find the correct setting for calibration is one option and the other one to ignore altitude.
    It is irrelevant whether you start from 51m oder 200m, but it makes a difference if you get 500m gain where you should only have 300m

    NOTE:If you need to adjust elevation gain and not absolute elevation, then you might have issues with your watch and may require Support to replace.
    Would you mind sharing an un-edited activity?