Inaccurate GPS

reflecx said:

Garmin 955 clearly does smoothing of GPS pace

They clearly use something like "rolling average of last x seconds (5? 10?)" instead of simply displaying the GPS pace directly. That is obvious.

reflecx said:

and it take 10-15s for small pace changes to be reflected on the watch

In my opinion more like 5, but yes, it is not instantly.

reflecx said:

It has some algorithm to detect large changes in pace though, and the smoothing doesn't kick in then

Of that I am not sure... But even with a rolling average of let's say 5 seconds, changes like mine above, going from 5:30 to 3:30 and then to 6:00 would be clearly visible.

I'm just telling you what I observe on my watch. Raw GPS data is actually very jumpy, it is difficult to know whether the difference in position is due to inherent GPS volatiility or actual change in pace, which is why smoothing is done. Even with smoothing, GPS pace is still not very accurate.

Try walking during your rest intervals and you will find that your Garmin picks up the change in pace quickly.

I think we are facing a bad implementation once again.

Position filtering it's something easy if you do that with the right math instruments, otherwise all you get it's crazy data.

I have an app installed on FR955 which tell me position and speed and that one is following almost instantly, so data it's there. That is what you want when you're training with pace targets.

You ask me to walk instead of running during rest period but that gives you a totally different training and I can't change the training because of my watch.

In my case I have 400 meter "fast" and then those 100 meters slow which are a 30 seconds interval and GPS is lagging so much that it just can't follow it.

Rolling average? Yes, maybe, but that's not working for this training, which is just a "normal" training.

Tried switching GPS to "All" instead of "Auto" but same result, this chart is awful Garmin-Sierra :

I was thinking that cadence may be something to look at.

I'm not changing my cadence (it's training again). So I'm 175bpm on the fast and 175bpm cadence on the slow leg. I don't know if the software "thinks" that I'm not changing speed because of this.

My GPS is also prety jumpy, this was with Multiband on, and my old 935 performs much better even in GPS only.

955

935

Is there something wrong with my watch?

Well, beautiful comparison.

And... all these crooked GPS segments by 955 compared with a straight line should result in a wrong GPS distance at the end of the ride.