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GPS offset?

nitzmahone

Supporting Member
Supporting Member
Feb 28, 2018
60
156
Portland, OR
Anyone else had an issue where your Model 3's GPS gets offset? I'd been parked in an underground garage for about 90m, and when I came out, it was consistently placing me about a block off wherever I was (so driving down the freeway, it thought I was driving parallel to it), which obviously makes the nav effectively useless. An "in-flight" touchscreen reboot didn't have any effect, but when I came back to it after being parked even further underground in another garage, all was fine. I'm on 2018.12.1...

I saw some mention of similar behavior on the Model S, with some people suggesting poorly shielded dashcam wiring near the antenna causing issues. I have a Thinkware F800 Pro with the rear camera wiring running front to back down the passenger side roofline, but I'd expect if that were the cause, it'd be pretty consistent (and the rear camera is just a Micro USB connection, not coax). Dunno where the GPS antenna wiring is though, either, but curious if anyone else had experienced this...
 

novox77

1.21 Gigawatts
Nov 25, 2017
1,642
3,554
NH, MA
This is normal for situations where you're parked and GPS reception is poor. It can take some time for the car to find enough satellites to make an accurate trilateration. The problem usually resolves itself within a minute or two.

This same issue is also why FSD cannot be primarily reliant on GPS for positional accuracy.
 

nitzmahone

Supporting Member
Supporting Member
Feb 28, 2018
60
156
Portland, OR
This is normal for situations where you're parked and GPS reception is poor ... The problem usually resolves itself within a minute or two.

Oh, it was totally stuck- my drive was about 25min on wide open roads/freeways during which it never corrected itself.
 

WestK

New Member
Apr 19, 2017
4
4
Fremont
Oh, it was totally stuck- my drive was about 25min on wide open roads/freeways during which it never corrected itself.
I have experienced this exact same problem on my 2013 MS. It seems to be a GPS reception issue and will normally clear up quickly with improved reception. I have also tried resetting the MCU (hoping the GPS subsystem would also reset) with mixed results.
 
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TT97

Active Member
Aug 6, 2017
2,173
2,911
Los Angeles
Oh, it was totally stuck- my drive was about 25min on wide open roads/freeways during which it never corrected itself.

Was the 25 minutes in constant motion? Freeway speeds? For GPS to re-triangulate, ideally, the car needs to be stationary. If you are moving the entire time, GPS has difficulty correcting. A reboot in motion wouldn't do much.
 

drawfour

Member
Mar 10, 2018
774
709
Seattle, WA
Just an anecdote and not related to M3, but I've had times where my iPhone (using Waze) was off by a a hundred yards or so. Constantly showing me not driving on the roads - like driving through houses and stuff. Usually that doesn't correct until you reduce speed significantly, like at a traffic light.
 
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gearchruncher

Active Member
Sep 20, 2016
2,186
2,728
Seattle, WA
For GPS to re-triangulate, ideally, the car needs to be stationary. If you are moving the entire time, GPS has difficulty correcting

This is really not true for any modern GPS. Your phone has no issue being told to start navigating once you are already moving, and you can happily reboot GPS units on airplanes in flight.

Locking on to a signal while moving takes longer. But "re-triangulating" is literally what a GPS does all the time while you are moving or not. This is a software bug in the MCU somewhere, not in the GPS.
 
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TT97

Active Member
Aug 6, 2017
2,173
2,911
Los Angeles
This is really not true for any modern GPS. Your phone has no issue being told to start navigating once you are already moving, and you can happily reboot GPS units on airplanes in flight.

Locking on to a signal while moving takes longer. But "re-triangulating" is literally what a GPS does all the time while you are moving or not. This is a software bug in the MCU somewhere, not in the GPS.

In addition to satellites, cell phones also use cellular towers for triangulation. As the cellular towers are much closer, a phone can triangulate much faster than the GPS in a car.
 

TT97

Active Member
Aug 6, 2017
2,173
2,911
Los Angeles
A Tesla is a cell phone.

I'm pretty sure a Tesla is a car.

I have never seen any reference that Tesla or any other car uses cell tower or wi-fi triangulation. If you have any articles on that, I would love to read them. Cars typically use dead reckoning when they lose satellite reception - which is what causes the car position to constantly be a block off.

While using cell tower triangulation can assist on quickly pinpointing the location, it doesn't have the accuracy you need for street navigation. Unlike a phone, you typically don't turn off your car in Seattle and then turn it on again a few hours later in NY.
 

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