So..the daft thing with the Alitimeter on fenix5

Garmin say the barometric Alt is more accurate than the Gps ....OK

They say to set the watch in Altimeter mode for better accuracy for sport where a change in elevation occurs..ok

They say calibrate manually to the correct height if known for best results..ok..or calibrate via GPS ..:rolleyes:...but they say that is not as accurate so do manually if possible and select auto Calibrate..ok

Now in an activity if you display the data screens "Elevation" and "GPS Elevation" and wait for the activity screen to get a lock, data feilds once the gps gets a lock it auto calibrates the Elevation to Gps Elevation:rolleyes:..mm but they say thats not as accurate so why do that, although in my case the GPS accuracy is always very close but the baro one drifts...mmmm

now after i press go the tracking will ignore the gps elevation use the Elevation from the baro altimeter sensor which drifts all over the place compared to the GPS elevation data field which remains accurate...:rolleyes: but that gets ignored in the track log:rolleyes:

once the log is in connect if i click "enable elevation correction" it will then be correct again presumably because it uses the map data.

this to me seems daft and just proves the baro altimeter just does not work very well at all.

why can we not just switch off the Altimeter and track and record the elevation changes with the GPS data as that actually seems more accurate despite what garmin say..this is the way my edge 1000 does it and that works great..

come on garmin help us out with this as it spoils the watch give us the switch off option...please

0 AllanOlesen67 over 7 years ago

Now in an activity if you display the data screens "Elevation" and "GPS Elevation" and wait for the activity screen to get a lock, data feilds once the gps gets a lock it auto calibrates the Elevation to Gps Elevation:rolleyes:..mm but they say thats not as accurate so why do that, although in my case the GPS accuracy is always very close but the baro one drifts...mmmm

The watch only does this if you do not have a previously recorded manual altitude calibration at that location. If the watch remembers an old calibration from the same location, that one will be reused.

So calibrate your altimeter manually once at each of those places where you intend to start activities - and do the calibration while you have a GPS fix so the watch knows where it is. Then you will not see the behaviour you described.

Regarding accuracy:
There are a lot of misconceptions about this. Your post contains some of them. You can't say that one of the two methods - GPS altitude or the barometric altimeter - is more accurate than the other. Both of them are less accurate than the other in certain well-understood situations:

For small elevation changes over short time, for example a run in a landscape with small 10-20 meter hills, the barometric altimeter is much more precise than the GPS. On the GPS, these elevation gains and drops will drown in measurement noise.
For large elevation changes, the GPS will be more accurate. It will still have the noise of 10-20 meter on every measurement, but if you climbed 2000 meter on your bike, that matters less. In this case the barometric altimeter will be less accurate since it relies on assumption about the density of the air between your start point and your end point, and this density will not be the same every day.
The barometric altimeter needs to be calibrated very frequently since it uses ambient pressure for altitude measurement, and the ambient pressure at a given location will change all the time. The GPS does not need any calibration.

I agree that for certain activities like the aforementioned 2000 meter bicycle climb, it could be nice to have a choice of using GPS altitude instead. But only for those activities.

0 BogWhoppitt over 7 years ago

Hi Thanks for the reply,
i had thought that was what auto calibrate did, it told the altimeter that the elevation at the location with the current gps lock was the correct and that it would remember that the same as a manual entry of a known elevation, given the GPS does give me the correct elevation at my home.

one odd thing yesterday was tracking a walk all was good elevations close enough...stopped for lunch at a pub paused watch to resume later when i restarted the elevation was at 8500ft and went haywire from there eventually showing no elevation, whilst the gps elevation data field remained spot on...and this was a very flat walk.

uploaded to garmin connect and it was the altimeter log which was of course useless.

would that mean i should have done a full known calibration upon restarting the log, as i would have thought it would know as it was on auto calibrate to gps..mmmm

thanks

0 BogWhoppitt over 7 years ago

All good until pause..:rolleyes:

0 AllanOlesen67 over 7 years ago

A recalibration should not be necessary in the situation you describe.

I think you have been hit by another problem: A lot of the newer Garmin watches seem to have problems with the ambient pressure sensor. They will be confused by static electricity from clothing, and sometimes also by temperature changes. So your ambient pressure measurement probably made an error, and then your altitude measurement went out the window. In that situation you will not get any benefit from an altimeter recalibration until the ambient pressure measurement has settled down again.

If you want to investigate this further, you can enable the Ambient Pressure data field in an activity in the watch, and then look at the ambient pressure in situations where you get an altimeter error. For example, will the ambient pressure freak out when you put on an acrylic sweater which generates static electricity? Will the ambient pressure change a lot when you come from cold outdoor conditions to warm indoor conditions? It shouldn't happen, but apparently it does for some owners of the F3 HR, the F5 and the 935.

I have an F3 (non HR) which allegedly uses another ambient pressure sensor, and I have not had any problems myself.

0 BogWhoppitt over 7 years ago

actually just trying again, the gps elevation feild is different to the altimeter elevation feild so it is not even auto calibrating the altimeter correctly from the gps lock.:confused:

will try the manual option but that seems real faff to do that for every location i start an activity especially as i would have to find that out the elevation or manually enter the gps estimate, but then is that not what the auto calibrate is meant to do:confused:

0 BogWhoppitt over 7 years ago

thanks for that allan that seems to make sense, guess its faulty or just random , either way its not doing what i bought it for...shame as i really want to like this watch and it does most things really well.

just need that off button..

cheers

0 AllanOlesen67 over 7 years ago

Your watch is probably calibrating to the last known altitude for that location.

This makes sense if the last known altitude was a manual calibration.

But if the last known altitude was just another GPS measurement at the start of the activity, it makes no sense at all. Why should yesterday's GPS altitude be any better than today's? I have seen this behaviour myself on the F3, and I consider it a design error. (But of course, yesterday's GPS altitude will not be worse than today's either, so this error will not make things worse - it will just make them weird...)

Anyway, if you make a manual calibration at the location where you experienced this, the manual calibration will take precedence in the future. So it is easy to make the error go away.

If you don't know the altitude for your position, you can watch the GPS altitude for 5-10 minutes and pick a value somewhere in the middle of the variation. I do not think that the watch has any functionality for automating this, though it could be a nice feature.

0 BogWhoppitt over 7 years ago

hi allan that makes sense , thanks, just tried the manual calibration of my home after gps lock and it does seem to lock back at that elevation ...

still not sure what the auto calibration is meant to do..:(

still though the random changes of the elevation due to either the static or pressure or temp during an activity still renders the device somewhat not fit for purpose, especially at the price sold.i guess its asking a lot , but Garmin sell this device to do just that and advertise it as such.

i use my device mainly Snowboarding, Hiking, Cycling so a reasonably close elevation would be useful , GPS elevation does give me just that, and i guess i can see that in the data field , but not in subsequent the uploaded tracklog...arghhhh

mines also shown me at -178000 ft..:D:D:D

Thanks again

0 BogWhoppitt over 7 years ago

As seen here:)

0 BogWhoppitt over 7 years ago

the other daft thing is on the connect website the elevation corrections button is disabled by default if your device has a barometric altimeter..

however with my walk above if i click the enable elevation correction it gives me the correct profile.....:D:D come on garmin have a look here....it all seems back to front...

but it doesnt sync that change the on the app.....