Fusedalti Source for the Race

[colinmacdon]

I am wondering what is the “GPS” source for the FusedAlti Data on the Race? The reason I ask, is that under my usage, the Race appears to have it’s elevation offset by 5-7 meters higher than the other watches/elevation sources, google earth, strava, etc.

I have had various GPS watches: Apple watch 3, apple watch ultra, Suunto 9, Suunto Vertical, Epix 2, Coros Apex 2 Pro, and now a Suunto Race.

I have a local route that I run which is a loop starting and ending at the same point. This route is 7km and pancake flat. According to google earth/strava it is 574 meters at the start/finish.

The Epix almost always reported consistent starting and ending altitude of 575 meters, with vary little deviation in max/min elevation.

Both Apple watches, mostly report 574 at the start/finish.

Suunto 9, reported 574 most of the time.

The vertical was 576.

Apex 2 pro was 578.

The Race, in contrast, all over the place, varying as much as 9 meters, but they average out to 581–seemingly 7 meters higher than reference.

I have played around with using the auto adjust elevation setting, and once it notifies me it is complete, I have seen everything from 565 to 589–running the calibration from the same location. 24 meters difference.

Not a big deal I suppose as long as it’s consistent (which it hasn’t been), but curious as to the offset.

[Brad_Olwin]

@colinmacdon Do not do an auto-adjust or manual adjust right before you exercise. I don’t for sure about the Race but this can cancel FusedAlti. I almost never manually adjust or auto adjust, I just let the FusedAlti do its job. Commuting 45k one way to work and back with 200m gain to work my altitude at home can be off due to changing weather. Once I do an outdoor exercise of any kind it is typically back to perfect. FusedAlti works well and I try not to interfere.

[colinmacdon]

@Brad_Olwin Gotcha. Thanks for the advice. I will cool the jets on the auto adjust and let the FusedAlti do the work. Just a point of clarification, isn’t the auto adjust doing essentially what the FusedAlti doing? Calibrating the elevation to a known GPS point? I’m not clear on how that would have unintended consequences, unless like you mentioned it would cancel FusedAlti?

[Mff73]

@colinmacdon
there is no “know gps” point : fused alti, like the auto adjust, is analyzing the GPS signals from the satelites, and calculate actual position altitude based on this.
If signal is good enough, auto adjust is setting the most correct value, and for fused alti, it is aimed to correct the altitude measured by watch baro sensor (with some algorythm for sure).
Answer to you question : no offline source of altitude, just outdoor instant measurements.

[colinmacdon]

@Mff73 said in Fusedalti Source for the Race:

actual position altitude

Where does this altitude come from? I must either be in the GPS message received by the watch along with the coordinates or, it cross references a database of known GPS/elevation points. And in the case of the latter, I am curious as to what the source of this is?

[Egika]

@colinmacdon you can read some wiki about how GPS works.
Basically, the GPS receiver is getting time stamps from different satellites in the orbit. From the time difference of the signals and the known positions of the stellites, the receiver can compute it’s position in the 3 dimensional sphere. With an underlying model of the earth, you now know your horizontal position and your elevation above MSL.

For your case you need to know, that the fusedAlti algorithm is only correcting the altitude if the difference is above a certain threshold

[Mff73]

@colinmacdon
no source : satellites are sending their relative position and with triangulation calculations, and based on a theorical earth shape, devices can estimate local altitude.
But Egika seems quicker than me

[Egika]

@Egika said in Fusedalti Source for the Race:

@colinmacdon

For your case you need to know, that the fusedAlti algorithm is only correcting the altitude if the difference is above a certain threshold

That means if the altitude is within like 20m (not sure of the exact number) of the actual value, FusedAlti will not change it.

[Brad_Olwin]

@colinmacdon This does not work as Garmin does. There is no reference as all is done continuously in real time. A better approach IMHO and in my direct experience.

[renton82]

@Brad_Olwin Totally agreed!

[colinmacdon]

@Brad_Olwin the latest run without adjusting altitude is much more consistent. Any idea about the elevation offset I am noticing? By various sources, the elevation that the Race is reporting consistently 7m above. If FusedAlti is correcting elevation, it is correcting it to an elevation that exceeds anything in the area.

[Egika]

@colinmacdon are you sure a correction did take place at all?
As above, if you are within a certain limit close to the real altitude, nothing is changed.

And btw out of curiosity: what difference do 7m make for training or anything else?

[pilleus]

@Egika said in Fusedalti Source for the Race:

the fusedAlti algorithm is only correcting the altitude if the difference is above a certain threshold

Before I start an activity with gps I calibrate the altimeter manually to the altitude of the start point. With best results, since I use Suunto watches.

Now a question to FusedAlti … in the manual of the Vertical (I think the process is the same as in the Race) I can read:

“Suunto Vertical uses barometric pressure to measure altitude. To get accurate readings, you
need to define an altitude reference point. This can be your current elevation if you know the
exact value. Alternatively, you can use FusedAlti (see 3.16. FusedAlti) to set your reference
point automatically.”

Does it mean, that FusedAlti is activated by default or must I choose it every time before the start of an activity (with the second option in the altitude settings)?

[taziden]

@pilleus said in Fusedalti Source for the Race:

Does it mean, that FusedAlti is activated by default or must I choose it every time before the start of an activity (with the second option in the altitude settings)?

It’s enabled by default and will correct the elevation after 15-20 min of an activity. No need to set the altitude manually. It only led to issues when I did it.

[pilleus]

@taziden said in Fusedalti Source for the Race:

and will correct the elevation after 15-20 min of an activity

I tested it today during my bike ride. At home I set manually a complete wrong altitude. Then I started the activity and after 8 minutes the altitude jumped to the correct value. It was randomly nearby a point which altitude I know, because it is the highest point at the beginning of the route.

In the altitude graph in Suunto app the jump is not plotted, the graph starts at the correct altitude of my home where I started with the complete wrong value. So it’s working fine.

A last question: I know the altitude of my start point and calibrate it manually before I start the activity. Is then FusedAlti blocked or is it working despite of the manual calibration (e. g. when the air pressure changes significantly)?

[taziden]

@pilleus said in Fusedalti Source for the Race:

@taziden said in Fusedalti Source for the Race:

and will correct the elevation after 15-20 min of an activity

I tested it today during my bike ride. At home I set manually a complete wrong altitude. Then I started the activity and after 8 minutes the altitude jumped to the correct value. It was randomly nearby a point which altitude I know, because it is the highest point at the beginning of the route.

In the altitude graph in Suunto app the jump is not plotted, the graph starts at the correct altitude of my home where I started with the complete wrong value. So it’s working fine.

That’s exactly as it’s supposed to work. Good

A last question: I know the altitude of my start point and calibrate it manually before I start the activity. Is then FusedAlti blocked or is it working despite of the manual calibration (e. g. when the air pressure changes significantly)?

Maybe it depends on the watch but on my S9PP (and I think it was the same on S9P), it would disable FusedAlti, hence giving me wrong elevation in the end. So I strongly recomend not to do that and never caliber by hand. Just let the watch do its thing

[renton82]

If you want to follow meteo variations you have to calibrate it, sometimes pressure changes rapidly and watch interpret it as altitude change (I’m talking about not during activities).

[pilleus]

@taziden said in Fusedalti Source for the Race:

it would disable FusedAlti

Temporarily? Or for the entire time of tracking an activity?

I never had problems with my SSU and I always calibrate manually the start point.

[colinmacdon]

@Egika said in Fusedalti Source for the Race:

And btw out of curiosity: what difference do 7m make for training or anything else?

It doesn’t. But in the same token, why wouldn’t it be accurate?

I had just noticed that in the 10 or so activities all but one (which I manually set) started/ended with an offset elevation. Hence I was curious if it had a source. The one I manually calibrated to the correct elevation before starting, finished with the offset elevation (7-8 meters higher).

I was just more curious to learn about the the FusedAlti and how it works. For my watch, whatever is shown in the widget for elevation (which I know varies with air pressure), is the elevation that the watch will start the activity with (correct or not).

In the area I run, here is the topo map:

Every other watch I have had, has been within this range, yet the Race has yet to be in this range.

Again, not a big deal.

Appreciate the insights, lots to learn.

[Mff73]

@pilleus
and others,
it don’t remember precisely, but i think spartan fused alti are not behaving like new models.
With new models, fused alti is able to fix altitude continuously, while with spartan it is “only” a global offset of the whole measurment.
But it was long ago