Request to improve Barometer performance (Fenix 7X Pro)

Tisztul_A_Visztula said:

We are heading toward sub-1m accuracy in 2D positioning

However, this does not apply to watches. Their antenna is not made for this.

Even with a GPSmap (65s) I can achieve a maximum accuracy of 1.2 meters in good conditions. And the GPSmap devices have a better (and externally mounted) antenna.

However, the greatest influencing factor remains the Earth's atmosphere. Differences in transit time caused by the atmosphere have an effect on accuracy.

I said “are heading” ;-). Anyway we are much closer to a vertical accuracy of 1.5 m than 400 feet, arent we?

Tisztul_A_Visztula said:

I have not much knowledge about accelerometers and gyroscopes, but if they are good enough to replicate the horizontal move under bridges, in tunnels, they evidently has to be good enough to replicate the vertical move. At least it is my logics.

Yes, if you know you are at relatively high know entry velocity, in a a practically 1D system, where the accelerometer is in a fix position, on a known trajectory, and you do not expect more than continuous driving with just a limited range of acceleration / deceleration, you can make some successful estimation of the speed and distance.

Not so with a watch constantly moving in all possible directions, and with a wild range of acceleration, permanently crossing the critical zero state on any of its axis (hitting so the hysteresis spot with zero sensitivity). The accelerometer has a limited sensitivity, it means there is certain hysteresis around the zero. And zero acceleration can happen both in static state, as well as during steady motion with constant velocity (i.e. in a lift, or climbing a slope of a constant grade, or driving in a car at a constant speed on a slope, etc.

The same goes for the gyro, which is needed to determine the orientation of the watch in the space. Besides the limited sensitivity, many Garmin watch models do not have gyro at all (F7 does have it, though). Without gyro you do not know in which direction the watch is acceleration, so the velocity or distance estimation is not possible at all, unless you have a system with the accelerometer mounted in a fixed way, so that it cannot change its orientation in the space at all.

Tisztul_A_Visztula said:

As regards the GPS accuracy let me highlight that you cited a 15-20 years old safeside Garmin statement mirroring the accuracy of the then consumer GPS receivers.

The vertical accuracy is much worse than the horizontal one because of a simple reason limiting the accuracy of the trigonometric functions - the visible satellites are all on almost the same plane. Only the most distant ones (with weak signal) are a little bit lower, because of the shape of the orbit. That makes the trigonometric calculation of the altitude more challenging than the triangulation of the position on the horizontal plane. 

Tisztul_A_Visztula said:

Sure, but if you are constantly using an accelerometer you have collected information about not just the previous acceleration data, but the previous speed data itself

You forget about the the sensitivity limits (the hysteresis problem). Principally it means you can guess distance for example at steps with relatively good accuracy, because the acceleration curve during the stride is well known, and rather dynamic, but in the moment you have long periods with zero or very low acceleration around the zero point, you do not know at all whether you are absolutely static, or moving for example with the speed of 10 cm per sec. Although it is a negligible and unimportant speed for the instantaneous analysis (like the Running Dynamics), in just over an hour, it would lead to the error of 360 meters, which is already unusable for any elevation adjustments.

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Oh, now I got it. I mixed up the horizontal movements and the vertical one. Even if your horizontal accelerometers can define your speed, but since normally you move slowly vertically, except for real climbing over 10%, your vertical accelerometer have no chance.

Or let me put it in another way. If you are walking at a grade of 1% or 2% at a speed of 1-2 m/s,  but your arm with the watch is wildly swinging, your watch may be good for elevation adjustment. But if you are walking on the same route and at the same speed, but you are checking for your watch for a minute, you have lost the chance to use it for the same elevation adjustment.

Is it a correct example?

Tisztul_A_Visztula said:

Even if your horizontal accelerometers

There is no horizontal or vertical accelerometer. The accelerometer gives a 3D acceleration vector which is based on the physical orientation of the watch (relative to the watch, not to the Earth). It does not know whether the watch is oriented vertically, horizontally, or at an angle. You need a gyro for that. Not all watches have it. And the gyro has a similar problem with the sensitivity and hysteresis as the accelerometer.