Incorrect GPS starting point causing shifted route

What no one ever tells you is that the green Garmin GPS ring is (sometimes) a lie. It usually appears very quickly when you're outdoors, but it doesn't always mean that you have a solid GPS fix.

I can tell that the watch doesn't truly have a solid GPS fix because I'm standing still, but:

- my location on the map screen is wrong

- the map screen shows that I'm moving

- the instant pace data field shows a pace that's changing wildly (and sometimes shows me running at impossible paces for a few seconds)

This especially tends to happen when I start my run near tall buildings (which is the majority of my runs, since I live in a high-rise apartment which is located near a lot of other apartment buildings).

What I almost always do is wait several seconds after the GPS ring for my instant pace to settle down to 0:00. Usually this takes less than 30 seconds, but in the worst cases, I've had to wait a couple of minutes. When I do this, it avoids the kind of problem that you posted about.

If I'm in a hurry and I don't wait, I have similar problems: my start position is wrong, the GPS track near the start is wrong, and my stats near the beginning of the run are wrong (incorrect distance, unrealistic pace). In this case, sometimes I'll crop the start of the run using Connect to get rid of the bad data (which also fixes the totals/averages).

It might help to add the satellites data screen so you can check before starting? Not sure if it shows how many are connected, signal quality, etc.

You should have a built-in data field called GPS that you could add to a custom data screen that shows the signal strength. But waiting will work too

Jacquers said:

You should have a built-in data field called GPS that you could add to a custom data screen that shows the signal strength

That is no different than looking at the GPS ring.

When the GPS ring is green, that data field will show full bars for GPS. Same goes if I write a CIQ app which shows the numerical value of the GPS fix (which is an integer from 0 to 5) - it will show 5 when GPS ring is green, but that doesn't mean I have a good lock.

And again, I cannot emphasize this enough, even when the watch claims that you have full bars / green ring / good GPS, it's possible that:

- your location on the map is wrong

- the watch shows you as moving when you are standing still, based on the instant pace field and the map

- the watch shows you as moving impossibly fast

- if you start the activity at this point (while the watch shows you as moving when you're standing still and in the wrong location), the GPS track and distance/pace stats for the first part of your activity will be wrong, just as in the OP).

I live in a high-rise apartment building complex (lots of tall buildings), so I see this behaviour almost every day. I get a green ring, but I have to wait longer for a real fix.

Not to state the obvious, but Garmin wants to show a solid GPS lock asap, bc users don't like to wait for GPS. But maybe it should be clear by now that Garmin is showing that solid lock a little too prematurely.

Iirc, Garmin watches from before FR935-ish (2017) would take forever to get a GPS lock. While this may have reflected older, worse tech where it actually did take longer to get a lock, at least when you got a lock it was more or less guaranteed to be "real".

Iow, newer Garmin watches probably do get a GPS lock faster than before. But I think they *also* lie to a certain extent about how fast they get that lock (i.e. they show a solid lock before they really have one).

It's not necessarily an intentional lie, but all I can say is that the practical result is that I don't know if I have a good GPS lock when I see the green GPS ring. The green GPS ring is necessary but not sufficient for a good lock.

Ah, ok, thanks. I'll keep it in mind for when I start activities. I live in suburbs, so no tall buildings nearby.

Pity you can't see a graphic of the satellites like this, would be handy.

 

Jacquers said:

Ah, ok, thanks. I'll keep it in mind for when I start activities. I live in suburbs, so no tall buildings nearby.

Yeah it's def more noticeable if there's tall buildings nearby.

Jacquers said:

Pity you can't see a graphic of the satellites like this, would be handy.

I don't think that would help the average user tho.

I think what would help is if the green ring did not prematurely appear on a consistent basis under certain conditions. Either Garmin hasn't bothered to make it as accurate as possible, or they don't want to (because then users would complain that it takes too long to get a fix).

It's also possible that they don't test around tall buildings / challenging conditions. Any tall buildings in Olathe, Kansas?

Hi everyone,

Small update from my side, as the issue happened again today, but in a less severe way.

The GPS signal took longer than usual to be acquired, but I waited until it turned green and stayed stable before starting the run.

However, during the first part of the run, the track was shifted, as if I was running on the other side of the avenue. Also, the GPS trace does not follow the street properly and sometimes goes straight through city blocks, instead of staying on the roads.

After the first part, the track became more accurate, but the beginning is still clearly incorrect.