GPS wobbles today?

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 deepsoup 21 Feb 2021

My (usually) very reliable Garmin watch recorded the first half of a run accurately this afternoon, then lost it a bit and claims I shot off at a tangent and finished several miles away from where I actually did.

I'm just curious whether anyone else noticed GPS weirdness this afternoon or if it was just me. 
(I was mostly in the woods at the time, but the watch is usually accurate to within about 10m or so regardless.)

In reply to deepsoup:

Just checked my Garmin Edge on the bike; all recorded accurately for my afternoon ride today.

In reply to deepsoup:

My Vivo active HR has been spot on today. 6.5 hours walking in open country.

 Cobra_Head 21 Feb 2021
In reply to deepsoup:

You probably lost the signal for a while, is this a usual route?

Post edited at 18:31
In reply to deepsoup:

Fine on my 245. I think there was another glitch with the almanac data this month, but I had no issues.

In reply to deepsoup:

I turned mine on for about 5 minutes to do a geocache with no trouble, and it hadn't been turned on for months.  You can find out when GPS jamming is occurring by looking here:- https://www.ofcom.org.uk/spectrum/information/gps-jamming-exercises

They're normally done out at sea around Scotland.

 flatlandrich76 21 Feb 2021
In reply to deepsoup:

I've no data for today but experienced exactly the same problem with my Satmap 12 once before. I was out in the open at the time (above Ladybower res) and haven't had any issues since so I'm assuming it was a satellite and/or signal issue. 

In reply to deepsoup:

> I was mostly in the woods at the time

Tree cover is a known problem with GPS, due to the signal attenuation it provides, especially  wet tree cover.

Added to the antenna orientation problem you get with a wristwatch (is it pointing at the sky or somewhere else?), this might explain your poor track.

What what the geographic environment? Any large rock faces or big hills nearby? They can give reflection errors (again, if the antenna orientation is sub-optimal, you may only be seeing a small number of satellites, or, indeed, only reflections).

 Andypeak 21 Feb 2021
In reply to deepsoup:

I have this issue quite regularly. I assume I loose the signal. 

 ThunderCat 21 Feb 2021
In reply to deepsoup:

I had some strava weirdness on the bike at around 3pm.

 girlymonkey 21 Feb 2021
In reply to deepsoup:

My watch recorded my ride this morning but still hasn't uploaded to the app. I have tried syncing it several times. My ride to work later on uploaded fine.  My watch still has the morning one saved though. Weird

 deepsoup 21 Feb 2021

Thanks all, just me then I guess.

In reply to Cobra_Head:

> You probably lost the signal for a while, is this a usual route?

Yes, very!  That patch of woodland is the nearest nice off-road place to home so I've been up and down and round and round it a lot since the start of lockdown #1.  Never had a problem before today, but I guess the satellites were just in a particularly awkward alignment this afternoon.

It seems a bit odd that it didn't recover over the ten minutes or so of city streets with a clear view of the sky heading home, but no biggie.  Seems to know where it is again now, despite being indoors.

Post edited at 21:54
 deepsoup 21 Feb 2021
In reply to girlymonkey:

Hm.  That is a bit odd. 

Is your watch one of the ones you can plug into a usb port on a laptop and copy/paste a FIT file (or whatever) manually?

 girlymonkey 21 Feb 2021
In reply to deepsoup:

No, just a bluetooth connection

 deepsoup 21 Feb 2021
In reply to girlymonkey:

Ah boo. At least with it still being saved on the watch I guess you can copy the headline stats across manually if all else fails.

 Cobra_Head 22 Feb 2021
In reply to deepsoup:

My old GPS used to do this under trees, especially if wet, it would lose the signal, and then seemed to take a while to pick it back up again, throwing the odd weird reading in there, hence the straight line.

 deepsoup 22 Feb 2021
In reply to Cobra_Head:

> My old GPS used to do this under trees, especially if wet, it would lose the signal, and then seemed to take a while to pick it back up again, throwing the odd weird reading in there, hence the straight line.

My old one did that once in a while, I upgraded to a second-hand 630* about six months ago and it's been rock solid with never a blip before now, even when the same trees still had most of their leaves and were gopping wet.
*(£50!  Bargain!  God bless people with money to burn who have to have the latest model. )

I wouldn't have posted if it had lost signal for a bit and put in a straight line to wherever it picked up again though, this was a bit weirder than that hence the curiosity.  It doesn't seem to have dropped out, the data points continue with a set of coordinates etc. every few seconds, but it's like it imposed a 'drift'.  As if I was paddling a canoe instead of running and there was suddenly a strong current flowing North. 

According to the track I suddenly went off the path at an angle, picked up the pace to about 1.5x what I was actually doing and ended up a couple of miles North of my actual finishing point.  (Having done a bit over 19km instead of about 14km.)

Post edited at 10:09
 Cobra_Head 22 Feb 2021
In reply to deepsoup:

Weird

 jkarran 22 Feb 2021
In reply to deepsoup:

> It seems a bit odd that it didn't recover over the ten minutes or so of city streets with a clear view of the sky heading home, but no biggie.  Seems to know where it is again now, despite being indoors.

I have a little navigation computer built it around a OEM gps module. It works fine once it has a lock but it's terribly slow to establish a lock if it's moving when switched on, 5 or more minutes of searching isn't unusual, especially if it's not been used in a while and it's constantly moving. Stationary it'll lock in seconds but stopping isn't always an option.

jk


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