Very poor GPC accuracy since last App update

[Brad_Olwin]

@Gilles-D It does take time for the watch to unpack AGPS files but these should be loaded sometime after midnight. We do not have much to go on here. Images or links to the activities would help some.

[Gilles D.]

Hello @Brad_Olwin ,
thanks for providing your help. I thought I had initially loaded 2 images of the workout, but I may have not done it correctly.
This is the link of the workout (public): https://www.strava.com/activities/11027839242
In the Lap part, you may see that loop 2 and loop 3 are 5.01 km and 4.83 km.
Yet the segment is 5.88 km (https://www.strava.com/segments/16570481?filter=overall).
I have been using Suunto products since 2016 with Ambit 3 Peak, switched to S9B in Septembre 2020, and I had never experienced such erratic GPS recordings.
Thanks,
Gilles

[isazi]

@Gilles-D I checked your track on Strava, and it seems quite good for a S9B, I do not see any section where it went crazy. Which satellites are you using?

[Gilles D.]

@isazi hello,
thanks for looking at my “case” and for your answer.
I am using GPS+QZSS.
Regarding the track : my concerns are :

• the distance measurement : on a 5.8 km loop, the watch measures 5.km the first time, and 4.8 km the second time. There is almost 1 km of difference on 5 km, it is huge!

• the pace variation : as you can see in the screenshot, there are very important variations in the pace, and it does not reflect the reality. I have added some comments to try to better explain the “case”.

Maybe the 2 points are connected together somehow?

[Brad_Olwin]

@Gilles-D From the satellite image it appears heavily wooded and the track looks good. I did measure the KM men and women for the track and indeed it is 5.8 km. Either the satellites are not detected well because of the tree cover or there is another problem. I assume you have run this before with past firmware and had 5.8km?

[Gilles D.]

@Brad_Olwin yes I ran it before, 2 months ago, with same firmware. This place is indeed a wood, and at this time like in January not many leaves. This is the workout in January 24, when I had no issue :
https://www.strava.com/activities/10504542974/overview
And you can see the pace is steady, which does reflect what happened during the workout :

[Brad_Olwin]

@Gilles-D see what happens next time, hopefully the last one had low satellite quality. Let us know.

[isazi]

@Gilles-D try with GPS+Galileo or GPS+Beidou

[Gilles D.]

@Brad_Olwin, @isazi hello!
So I came back on same road, but this time with a new watch (I bought Suunto Vertical in between, I was a bit fed up with my S9 baro not being maintained any more from a software perspective…#obsolescence?).
And guess what : same issue with regards to distance measured by GPS vs reality on the ground : missing around 1 km around the same loop.
Strava track : https://www.strava.com/activities/11075937052

I don’t know what is going on. There is a military air base just next to this wood : can the GPS signal be affected somehow? It would be strange, because I have been running many times close to it, without noticing this kind of discrepancy.

Thanks anyway for your time and advises on this topic.
Regards,
Gilles

[Gilles D.]

@Gilles-D I was tired with the maths…Sorry
13.3 - 7.8 = 5.5 km, still some meters missing. I also did the theoretical distance of the run : 20.4 km vs 19.3 km measured during the workout. Puzzling.