GPS Connection

[EllyBrandi]

Hi, I am a new member and the proud owner of a Mavic 2 Pro. I enjoy flying fixed wing radio control and dabble in helicopters.
I am posting this more as a matter of possible interest than any problem with a drone but there may be a link here.
I am a cyclist and a few days ago I was riding downhill and noticed the Garmin 1000 computer I use was reading about 9 kmph. I was doing at least 30 at the time
. The road is a dead end and maxes out at about 18 %. I reached the turn around point and according to the Garmin I did a U Turn at 22 kmph ! I thought it strange and started riding uphill and the Garmin read 66kmph.. Clearly impossible uphill I thought.
To cut the story short I returned home and viewed the file. I have included a screenshot of the course the Garmin thought I was on. The road ( Toolunga) is a bitumen Rd and apparently I was out in the paddock, over the fence and up and down the road!
The Garmin returned to normal as I climbed the Hill. I have ridden this hill many times with no interference.
My question is, was there a problem with satellite reception, did the Garmin chuck a wobbly or what? If I was flying the drone at that point it may have been in a spot of bother. I don't seem to be able to attach the ride file from the Garmin for some reason, if anyone is interested and can let me know how, I will do so. The .fit file is greyed out when I try to attach it. I have also tried .gpx but it too is greyed out.

 

[Meta4]

The Garmin returned to normal as I climbed the Hill.

That is probably the key to the mystery.
Up on high ground, you had a good spread of satellites but when down low the higher terrain was blocking reception of enough sats to cause problems.
Your own body would have contributed to blocking any that were behind you.
It sounds like you stumbled on a combination of a time when the sats in your sky were either bunched close together or were blocked buy terrain or your body.
That left the GPS unit without a good 3D fix and giving inaccurate position information.
Those dead-straight lines going off the page look like the GPS joining the dots between fixes

If I was flying the drone at that point it may have been in a spot of bother.

Probably not ... but if you did, it would only have happened if you flew low down where sat reception was blocked.

I don't seem to be able to attach the ride file from the Garmin for some reason, if anyone is interested and can let me know how, I will do so. The .fit file is greyed out when I try to attach it. I have also tried .gpx but it too is greyed out.

They wouldn't help much anyway.
They don't give lots of data like how many sats you were picking up.
They just show where the GPS thought it was - the same as the map you attached does.

 

[EllyBrandi]

That is probably the key to the mystery.
Up on high ground, you had a good spread of satellites but when down low the higher terrain was blocking reception of enough sats to cause problems.
Your own body would have contributed to blocking any that were behind you.
It sounds like you stumbled on a combination of a time when the sats in your sky were either bunched close together or were blocked buy terrain or your body.
That left the GPS unit without a good 3D fix and giving inaccurate position information.
Those dead-straight lines going off the page look like the GPS joining the dots between fixes

Probably not ... but if you did, it would only have happened if you flew low down where sat reception was blocked.

They wouldn't help much anyway.
They don't give lots of data like how many sats you were picking up.
They just show where the GPS thought it was - the same as the map you attached does.

Maybe all the stars were aligned but I’ve been riding this hill for 15 years (slow learner) with no problems.

 

[Meta4]

Maybe all the stars were aligned but I’ve been riding this hill for 15 years (slow learner) with no problems.

You occasionally see weird arrangements of the sats.
I'used GPS for 20 years and once it had my car traveling at 1000 km/h for a minute or so on open ground.
It was just a rare temporary glitch.

 

[brett8883]

That GPS rollover thing was this week maybe that affected the Garmin, idk. But Mavic doesn’t have this kind of problem.

 

[Meta4]

That GPS rollover thing was this week maybe that affected the Garmin, idk. But Mavic doesn’t have this kind of problem.

The GPS rollover thing only affected GPS units made 20+ years ago.
Garmin didn't make any cycle GPS units back then.
Affected units did not give poor quality fixes they had problems getting any location fix at all.