Elevation and GPS

I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark

On Sat, 15 Aug 2020 06:37:14 -0700 (PDT),
wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56
miles with 1040 feet of elevation. I did all the hills one can
do in the flatlands. I go to Ride with the GPS and it shows
+1533 and then -1540.I am going to assume that it records the
elevation change at 1533. So what gives the two are off by a
pretty good margin? Strava seems to just take what Garmin
Connect says?

I expect this is a difference in how small changes in elevation
are accounted for. As an example, with the old Avocet 50, one had
to get more than 30 feet in elevation gain before it would start
accruing. You could cover 50 small rises of 20 feet each and show
zero accumulated climbing. So most likely, the Strava and Garmin
algorthims exclude such small gains, and rwGPS does not.

--
Ted Heise West Lafayette, IN, USA

On Sat, 15 Aug 2020 13:49:53 +0000 (UTC),
Ted Heise wrote:
On Sat, 15 Aug 2020 06:37:14 -0700 (PDT),
wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56
miles with 1040 feet of elevation. I did all the hills one
can do in the flatlands. I go to Ride with the GPS and it
shows +1533 and then -1540.I am going to assume that it
records the elevation change at 1533. So what gives the two
are off by a pretty good margin? Strava seems to just take
what Garmin Connect says?

I expect this is a difference in how small changes in elevation
are accounted for. As an example, with the old Avocet 50, one
had to get more than 30 feet in elevation gain before it would
start accruing. You could cover 50 small rises of 20 feet each
and show zero accumulated climbing. So most likely, the Strava
and Garmin algorthims exclude such small gains, and rwGPS does
not.

Oh, just to add a point that some cutoff is probably needed to
reduce noise from minor variations in barometric readings. It's
not a highly reliable measurment, though moreso than elevation
from GPS.

--
Ted Heise West Lafayette, IN, USA

On Saturday, August 15, 2020 at 3:37:16 PM UTC+2, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark

Both in Strava and Garmin Connect you can correct the elevation measurements of your Garmin device.

Lou

On Saturday, August 15, 2020 at 12:22:01 PM UTC-5, wrote:
On Saturday, August 15, 2020 at 3:37:16 PM UTC+2, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark
Both in Strava and Garmin Connect you can correct the elevation measurements of your Garmin device.

Lou
My understanding is that I have a barometric altimeter and therefore is suppose to be accurate. Maybe now with the all the data from GPS readings the one they calculate without using it is more accurate?

Deacon Mark

Op zaterdag 15 augustus 2020 20:43:25 UTC+2 schreef :
On Saturday, August 15, 2020 at 12:22:01 PM UTC-5, wrote:
On Saturday, August 15, 2020 at 3:37:16 PM UTC+2, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark
Both in Strava and Garmin Connect you can correct the elevation measurements of your Garmin device.

Lou
My understanding is that I have a barometric altimeter and therefore is suppose to be accurate.

When the weather is stable and your device is calibrated,
yes. A rain shower or a thunderstarm can already mess things up.

Maybe now with the all the data from GPS readings the one they calculate without using it is more accurate?

No GPS sucks at altitude measuring while riding along.
The correction used is based on data measured by a Space shuttle flight in think it was and is free to use.

Lou

On Saturday, August 15, 2020 at 2:52:44 PM UTC+1, Ted Heise wrote:
On Sat, 15 Aug 2020 13:49:53 +0000 (UTC),
Ted Heise wrote:

Oh, just to add a point that some cutoff is probably needed to
reduce noise from minor variations in barometric readings. It's
not a highly reliable measurment, though moreso than elevation
from GPS.

--
Ted Heise West Lafayette, IN, USA


Ted's explanation. I've never had a bike computer with elevation that didn't require some kind of baseline rise minimum as a stabilising measure -- what the designers probably described as "noise elimination".

All the same, I would be very surprised if even a cheap modern system, working off GPS, consistently gets it wrong. I'd take that 7 feet in 1540 any day as accurate enough. As an old sail circumnavigator, I know only too well how unreliable the natural ambient barometer can be -- it is an instrument (courtesy title) on which you interpret trends rather than particular pinpoint readings.

Andre Jute
I'm much less paranoid now that my life doesn't depend on guessing the cause of minuscule local changes in air pressure

On Sat, 15 Aug 2020 11:43:22 -0700 (PDT), "
wrote:

On Saturday, August 15, 2020 at 12:22:01 PM UTC-5, wrote:
On Saturday, August 15, 2020 at 3:37:16 PM UTC+2, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark
Both in Strava and Garmin Connect you can correct the elevation measurements of your Garmin device.

Lou
My understanding is that I have a barometric altimeter and therefore is suppose to be accurate. Maybe now with the all the data from GPS readings the one they calculate without using it is more accurate?

Deacon Mark

But a barometer doesn't accurately measure altitude unless it is
calibrated, almost for the moment, as atmospheric pressure changes not
only with altitude but with temperature, moisture content in the air
and so on. Read up on "altimeter setting" in any article about flying
https://www.aircraftcompare.com/blog...timeter-works/
https://www.faa.gov/air_traffic/publ...section_2.html
--
Cheers,

John B.

On Saturday, August 15, 2020 at 6:37:16 AM UTC-7, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark
The elevation measurement on a Garmin is a barometric pressure unit. Between the time you left and the time you returned the pressure changed so that in fact is a TINY change of only 6'. Around here we can have a difference between morning and afternoon of up to 20'. While it is possible for a satellite link to measure altitude changes it is inaccurate and depends entirely on the SATNAV satellites being on or very near the horizon.

On Sunday, August 16, 2020 at 12:04:34 AM UTC+1, Tom Kunich wrote:
On Saturday, August 15, 2020 at 6:37:16 AM UTC-7, wrote:
I have a garmin 910xt that on Garmin Connect says I rode 56 miles with 1040 feet of elevation. I did all the hills one can do in the flatlands. I go to Ride with the GPS and it shows +1533 and then -1540.I am going to assume that it records the elevation change at 1533. So what gives the two are off by a pretty good margin? Strava seems to just take what Garmin Connect says?
Deacon Mark
The elevation measurement on a Garmin is a barometric pressure unit. Between the time you left and the time you returned the pressure changed so that in fact is a TINY change of only 6'. Around here we can have a difference between morning and afternoon of up to 20'. While it is possible for a satellite link to measure altitude changes it is inaccurate and depends entirely on the SATNAV satellites being on or very near the horizon.

I used to have a Ciclosport that would give wildly different readings depending on whether you wore it on your arm or on the handlebars. Body temperature was much more upset than it could bear. It also broke on the day after the guarantee ran out, and I didn't even consider replacing it. POS. Scroll down at
http://coolmainpress.com/BICYCLINGgazelletoulouse.html
for a photo of it.

Andre Jute
I hate equipment for which I have to make excuses