Altiude measurement issues

[guenthi]

Hi,

I’m using the Peak 9 for a year now, but I still haven’t understood how altitude measurement works, and sometimes it seems strange.

A recent mountainnering example:
I calibrate the watch in the morning at 2755m (Vernagthütte), then I start recording (mountaineering mode) and go up…
The peak is reached at 3770m (Wildspitze), where the watch however shows me 3730m, which is not very accurate, I would say.

When I use another GPS device, e.g. iPhone, it immediately tells me we are at 3770m +/- 2m.
Visibilty and weather all around good, no reason for any deviations.

How is the height determined in the Peak 9 during my recorded training?
Is it from GPS (strange that it would 40m away), or baro (also strange that it would be so far away when weather is stable), or FusedAlti (don’t know how this actually works)?

If anybody knows some details or insights, I would be glad to learn what goes on here…

This behaviour happened already several times to me, and I think that being 40-50m wrong in altitude in good conditions should actually not happen.

Thanks for any clarifications!

[isazi]

@guenthi if you manually calibrated altitude before the start, you disabled FusedAlti.
FusedAlti uses GPS to calibrate altitude automatically during the activity, if the baro altitude is very different from GPS altitude (and GPS vertical error is low).

[guenthi]

@isazi Thanks for the quick reply - so what does that mean in my case, I calibrated before starting an acticvity, but GPS is used during the activity for recording the track, but height is no more adjusted then with FusedAlti?
This seems strange to me… can you explain this a bit more, or do you know where I can find more information about how the Peak 9 behaves for altitude measurement?
Thank you!

[isazi]

@guenthi said in Altiude measurement issues:

@isazi Thanks for the quick reply - so what does that mean in my case, I calibrated before starting an acticvity, but GPS is used during the activity for recording the track, but height is no more adjusted then with FusedAlti?

Exactly what you say. I never manually calibrate my watch, and just rely on FusedAlti to do it during the activity, because it works really well. If you manually calibrate you disable FusedAlti (not sure for how long though).

Hope you had a good time in Ötztal, haven’t been there in few years.

[Brad_Olwin]

@guenthi what @isazi says. I do not manually calibrate either. I am in the mountains every weekend, my altitude data are usually quite accurate.

[thanasis]

@Brad_Olwin i am curious why would prefer gps adjusted altitude rather than just barometric adjustment if you can calibrate the altimeter based on certified height for instance .

Based on similar posts here in the forum I was using the automatic calibration and In several occasions where I was by the sea, I tended to get -11 or -8 m readings. On the contrary by setting the actual altitude I was very spot on on my other readings .
So I miss something here ?

[freeheeler]

@thanasis
yes maybe… it could be that the idea behind FusedAlti is that you can focus on your sport without playing around with setting the altitude frequently during long activities with stormy, changing weathers?
11m wrong looks like a lot when you’re standing at the sea. when you are in the mountains at 3’000m, being 11m wrong is not so critical… I know some people would disagree here…

[DMytro]

@freeheeler funny story, a year ago I was climbing my first 3k mountain, at the top the watch has shown just 2998m which was a putty XD.

[freeheeler]

@DMytro
I observe very precise measurements very often, too.
but some meters off is within tolerance IMO.
also when we take into account how complex this feature is

[DMytro]

@freeheeler not saying otherwise, just a pity that the watch didn’t justify 3k XD.

[freeheeler]

@DMytro
aah …next time, climb the summit cross

[Panagiotis Kritikakos]

There is good explanation with examples on the following link regarding pressure and GPS altitude readings: https://xcmag.com/news/gps-versus-barometric-altitude-the-definitive-answer/

I have also experienced negative values on sea level, both when getting to sea level from higher altitude as well as when trying FusedAlti for auto-adjustement. During activities on mountains I can’t recall having any (major) issues with readings as they were mostly accurate.

I think S9P misses the ability to get manual pressure set as it existed in A3P for instance.

[freeheeler]

@Panagiotis-Kritikakos
edit: sorry, you asked for pressure, I already answered it is possible but that’s only true for altitude… yes, setting the pressure is not possible, but also not really necessary as only relative pressure matters IMO

[Panagiotis Kritikakos]

@freeheeler I also mean relative pressure, not absolute. For example, today I noticed difference by what the watch was reading and what the nearest weather station was reporting ~1.5km away in direct line and same sea level. Not sure if pressure can be sligtly different in such short distance with same conditions. I suppose other factors can affect the watch and I pressume the station is reporting correctly.

[freeheeler]

@Panagiotis-Kritikakos
that’s what I mean… doesn’t matter if the station shows different than your watch. what matters is, that if the station drops e.g. by 3 hPa over night, that your watch (if close enough to the station) drops 3 hPa, too