Alimeter issues

Hi,

I have Fenix 5x+ ver. 4.65 Rel (4d836d8); GPS 2.24. During Activities no 1 and 2 I had 4.20 firmware.

I found few things I would like to share here and get information if it is normal situation or maybe I should change some settings in my watch.

Maybe somebody had this kind of problem and got the solution.

Autocalibration of Altimeter I set ON (Continuous). Also I set up Autocalibration when there is no Activity.

My questions are:

1. what kind of algorithm is used to make autocalibration? According to DEM or GPS?
2. why there is no option to choose autocalibration method?
2. how often is it made?
3. how can I set up in Garmin Connect that I want to see alitude but GPS Altitude?

what I noticed is:

1.
Below there is activity (that time the firmware was 4.20):

https://connect.garmin.com/modern/activity/2955312861

this Lake. Lago di Misurina is more then 1700 m. According to data from the watch it is 1250m. I had autocalibration ON Continous mode but there was no option auto calibration according to GPS or DEM algorithm. when I saw there is a problem with altitude I made it in manual mode after few minutes (there is a peak on the graph).

question is why I had this situation?

2.
similar situation is here (also that time firmware 4.20) when I was climbing on Cima Grande:

https://connect.garmin.com/modern/activity/2948329975

https://connect.garmin.com/modern/activity/2947760010

Cima Grande is about 3000m peak. on my watch there was no value which would be close to this number.

In my opinion the problem is that autocalibration is made according to cartographic data and not GPS data. I agree that cartographic data (DEM algorithm) is good solution but in case of this tower - peak it totaly failed. If there would be possibility to use auto calibration method in GPS algorithm/mode I think there would be no this kind of situation.

3.

I made also tests with firmware 4.65. (GPS 2.20). I think GARMIN change something. When I turn on activity in the city (auto calibration is ON Continous) the altitude was changed (calibrated) according to DEM calibration (GPS was different)

But autocalibration is made still with DEM method. I also made one more test:

https://connect.garmin.com/modern/activity/3034049645

I was on the plane. I wanted to check how it works with auto calibration. I wanted to be sure which algorithm is used to calibrate altimeter.

I am almost sure that the watch is trying to use DEM method to calibrate the altitude. not GPS. The user (I do not know why) is not able if he prefer to use DEM nor GPS algorithm (in auto mode. in manual mode you can choose it).. And that's why information about altitude which I have in Activity is false. Altitude according to GPS was true. but I can't see it in my Garmin Connect because only information about Altitude (which was wrong) is saved. if there would be AutoClaibration option according to DEM or GPS it would solve the problem (in this situation I could choose GPS auto calibration option).

Of course I know that the reason is stable preasure in the aircraft cabin but it shows one important thing: if you are at some point which is as tower, highest point (Wall) you won't get true information about altimeter in this mode. the watch will change it using DEM method.

if you climb (not go but climb with rope, like I did in activity on point no 2) to the peak which is kind of tower (and that tower is arround the flat place) then there will be a problem with correct information on the watch (Altimeter) if I have AutoCalibration ON. and at this moment there is no good solution. If I set it OFF. I can have problem with air preasure.

- autocalibration is ON Contionous. advantages: I don't have to make manual calibration, I do not worry about weather condition and changing air preasure arround me. disadvantage: DEM algorithm is wrong in that kind of places like towers. cartographic data which are used are not so detailed in case of peak with tower type. example: point no 2 and Cima Grande.

- autocalibration is OFF - bad solution. I have to think about it all the time, there could be a problem with changing air preasure, here I can choose if I use DEM or GPS calibration (and this option should be in autocalibration settings)

Solution for this problem in my opinion:

possibility of setting which method should be choose when I use auto calibration method.

why?

well, if I can use autocalibration with GPS not DEM during this climbing I have: no problem with changing air preasure during whole day, I have no mistake caused by DEM (cartographic) method. Probably, I would be able to get +/- 10m accuracy of my alittude. here I got +/- 150m or more...

if I use Forrerunner (no barometer) I could get better information about my position and altitude.

also, in the plane if I have autocalibration option according to GPS not DEM also I could have correct values of altitude.

4.

by the way, whay there is wrong information about speed (point no 3)? it was a plane. on the watch I got more then 800 km per hour. Also, when you see basic data about activity you see:

655 km distance, 58 minutes, 201 km/h average speed. ... it is quite easy to calculate that average speed is not 200km/h but about 700km/h. Speed graph also shows that the speed was not higher then 200km/h but on the watch I saw more then 800km/h. why there is difference?

5.

if I make calibration of Alitmeter in manual mode and I am on 200m and put there 2300m, should the watch change this value (I have settings AutoCalibration ON (Continous)) when I start Activity?

6. Auto Calibration during non activity time. Watch is not moving. (during night)

I have question here.

Auto Calibration I think is working properly. I leave on 200m and even I have other value at the end of the day (i.e. 190) when I woke up I have 200m. Usually.... but last night the weather changed during night and I woke up with 220m. I have watch mode AUTO (barometer/altimeter). but why the watch thought the altimeter is changing if there was no movement? (the watch was on the table near by bed, zero movement). it should check if any sensor see movement or not, isn't?

how often autocalibration is made with no activity?

Waiting for your advices...

0 AllanOlesen67 over 6 years ago

I have no answers to 1-5, but I agree with your analysis of what happened in the described situations.

Regarding no. 6:
I don't think anyone outside Garmin know the precise algorithm for automatic switch between barometer mode and altimeter mode. But one of the main factors (at least for the old Fenix 3) seems to be the rate of ambient pressure change over time.

If the ambient pressure is changing fast - faster than the weather would usually change it - the watch will assume that you have moved to another altitude, instead of assuming that a weather change was the cause.

I don't know if inputs from accelerometers also play a role. I have never heard that it did, though your reasoning makes sense.

So my guess - if the F5X+ works as the F3 did - is that the ambient pressure at your place changed so quickly that the watch decided that it was unlikely to be a weather change. So it went into altimeter mode and adjusted the altitude instead of staying in barometer mode and adjusting the barometric pressure.

0 Merkur41 over 6 years ago

Hi,
I'm trying to answer some of the above based on own experience.
- Pre BETA 4.65, there have been ajor problems with the altimeter, so I wouldn't see any tests pre this version as reliable.
- As per the manual (p.29) Auto calibration uses GPS. The way I read it, it automatically calibrates the altimeter at the beginning of an activity (that uses GPS) based on the initial GPS fix. Or, if you activate "not during an activity", it calibrates it, whenever you inittiate GPS.As such, this is not a constant thing. - You have to interpret all your tests/readings based on this Garmin statement.
- in rgds to your point 5: I personally would not my watch to change after I calibrated it to a certain value. In my case - this is skydiving and I wnat the ground to be zero, independant from it's actial altitude abovee sealevel. That is why I disable auto-correct for this.If, in your case, you have set Auto Calibration to "on", the watch needs a GPS fix, after which it should change to the actual GPS based altitude.

0 AllanOlesen67 over 6 years ago

- As per the manual (p.29) Auto calibration uses GPS. The way I read it, it automatically calibrates the altimeter at the beginning of an activity (that uses GPS) based on the initial GPS fix. Or, if you activate "not during an activity", it calibrates it, whenever you inittiate GPS.As such, this is not a constant thing. - You have to interpret all your tests/readings based on this Garmin statement.

This would not be the first time a Garmin manual is out of sync with the behaviour of the device.

KrzysiekG's experience indicates that the watch uses DEM data for the calibration.

And this is also what I have seen in earlier threads on the subject.

0 Merkur41 over 6 years ago

AllanOlesen67 - I do not necessarily agree, that his experience indicates the use of DEM.
I still think that the manual at least gives the intention of the watches bahaviour. That this in various cases does not match it, is ,in my experience, in most cases caused by SW flaws rather than a wrong manual.
What has not been taken into account - at least from the description it is unknown to me - which GPS values he uses for comparisson. From the same watch or another reference unit (which IO always prefer in order to narrow down problems). The watch GPS appears to also have (had) issues at various GPS firmware versions. Finally GPS reception in cities (example 3) can also be tricky and is not necesarrily linked to the watch.

0 AllanOlesen67 over 6 years ago

AllanOlesen67 - I do not necessarily agree, that his experience indicates the use of DEM.

As I understand his description of what he has seen: If he starts an activity at a point where he is above terrain altitude, for example standing in a tower, then the watch will autocalibrate to the altitude of the terrain, not to his actual altitude in the tower.

If that description is correct, and the behaviour is consistent, then it is a quite clear indication that DEM altitude (or some other stored altitude) is being used instead of GPS altitude, no matter what the manual says.

It should be easily testable if you have access to a tower or a long, high bridge. So I will try it out the next time I am near to such structures.

0 Krzysztof over 6 years ago

you can try to do it at the balcony at high floor. should be enough if there will be no building arround. in my case I have 15-20 meters of difference and I am sure the calibration is according to DEM.

my tests:

1. climbing on Cima Grande - wrong altitude information
2. test in the aircraft. auto calibration is ON during activity, I should have similar or the same values "Wysokosc" and "Wysokosc GPS" (Wysokosc is Altitude). See the movie:

https://drive.google.com/drive/folders/1cV7JNDvMKpq7qCxPi7Oyp5fRp9VFBN1z?usp=sharing

if it is autocalibration not according to GPS for sure. Stable "altitude GPS" and stable but totaly different "altitude". even if GPS in this firmware works not OK why it doesn't update and calibrate the altitude?

and I think it is not a problem with altimeter in device but in firmware which make wrong calculation or using wrong algorithm or because the user is not able to choose best for him way of calculation algorithm which can depend on situation where you are.

also there was a problem that speed on the watch was quite real (850 km/h) but in Garmin Connect the speed which is on the graph was totaly untrue (200km/h). why?

0 Krzysztof over 6 years ago

AllanOlesen67 -
What has not been taken into account - at least from the description it is unknown to me - which GPS values he uses for comparisson. From the same watch or another reference unit (which IO always prefer in order to narrow down problems). The watch GPS appears to also have (had) issues at various GPS firmware versions. Finally GPS reception in cities (example 3) can also be tricky and is not necesarrily linked to the watch.

The movie above shows that I set up two different fields on the watch. Altitude and Altitude GPS.

0 Krzysztof over 6 years ago

It should be easily testable if you have access to a tower or a long, high bridge. So I will try it out the next time I am near to such structures.

let me know after yout tests

0 Former Member over 6 years ago

I still have Firmware 4.20 and can confirm that Auto calibration during activity until this Firmware Version unfortunately does not work at all. That is a pity as for me a good Altimeter is a key feature of an outdoor watch. I hope Garmin is going to fix that.......

I experimented with the Auto calibration at some hikes in the alps:

Before starting ahike I manually calibrated the known altitude. I experienced that the shown altitude always was quite off when I passed landmarks with known altitudes like mountain lodges, alps or summits. It was usually off between 30 to 150 meters (100 to 500 feet) although each time I passed a known altitude I manually calibrated the altimeter to the correct altidude. One time I passed a mountain lodge at 2077 m (6800 feet) and I manually calibrated the altimeter there (altitude was 50meters low, 164 feet). For the following about 300 meters in altidude the altimeter was roughly right then I would say. But then the altimeter suddenly corrected the shown altidude 150 m (500 feet) lower. On the summit then at 2650 m the altimeter showed a bit under 2500m. I experienced the same behaviour on another summit. So for the Moment Auto calibration is useless for me. So I turned the Auto calibration off with the known disadvantes of barometric measurement. But still better than Auto calibration.

I have a data field "GPS Altidude" when hiking (in the mountains): The shown GPS Altitude is much more correct than the Auto Calibration altitude or altitude with barometric measurement. So I hope it should be possible to fix the Auto calibration by changing the algorithm that might be too focused on the DEM.

I had the Suunto Ambit 3 before with the fused alti technology. That worked amazingly well in ascents. In 3,5 years I never had to calibrate it during an activity in ascents. It always showed the correct altidude on summits for example usually not more than 1 or 2 meters off.in fast descents like with ski or bike the altimeter was sometimes a bit off but not more than 50 meters in altidude.

By the way DC Rainmaker posted an Email by Garmin in his Review to the Fenix 5 plus series how the "new" calibration works:

"We’ve improved the in-activity auto calibration for the altimeter by leveraging the DEM provided in our preloaded cartography data. Our new default is now “Continuous” mode (Settings > Sensors > Altimeter > Auto Cal. > During Activity). This continuous calibration setting enables an algorithm that uses both DEM and GPS elevation as references to offset any altimeter drift due to weather-related pressure changes during an activity. These improvements are provided in a long-term manner without sacrificing the main benefit of a separate altimeter sensor on the device: the ability to accurately track short-term elevation change and provide responsive elevation-related data during an activity (e.g. hill repeat workouts). Note: the At Start calibration also occurs when Continuous is enabled.
We’ve added an altimeter calibration for watch mode as well (Settings > Sensors > Altimeter > Auto Cal. > Not During Activity). Assuming a user has enabled the use of location data on GCM, we will use the phone position along with the DEM provided in our preloaded cartography data to attempt a calibration each night during a user’s sleep window.
An additional option was added under manual calibration that allows a user to utilize the unit’s built-in DEM to calibrate the altimeter."

0 Former Member over 6 years ago

Schwammerl, I had this same issue. I synced it to garmin express and then did a full reset of the watch (you'll lose all your settings and widgets). After applying all my settings etc I have had no problems since.
Give it try.

Best