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How does the car know where it is on the map?

NedH

Member
Feb 27, 2019
154
154
GA
I'm interested in knowing how my car knows where it is on the map

I don't think there are GPS receivers so is it inertial navigation? Dead reckoning?

The reason I ask is that since my last update (2021.12.25.7) my car screen-map shows my car location sometimes blocks away from its actual location. Usually lasts only a few minutes but happens almost every day at the beginning of every drive. Happens both when navigating and just driving.

Also the screen will stutter/freeze for a few seconds when the location is incorrect.

I have re-booted numerous times. I have a service appointment scheduled but I wonder if anyone else is experiencing similar issues.
 

Darmie

Super Member
Supporting Member
Jan 13, 2016
2,062
1,364
Clear Lake TX.
You may have an issue with the GPS antenna. Have you installed anything in or on the car? Radar detector ect?
I would recommend your service request. There is always a chance they can log in remotely and see if anything is showing up in any log files. You can give them a call and if you get a human, they can look into this for you. You can always try a full reboot and see if that may improve. I keep reading where a wheel or tire size change on the screen will do a full reboot.
Any yes, there is an actual GPS receiver.
I've experienced a GPS freeze on our 17 model S once but the next day it was working.
On our 2018 X we had one time the nav arrow had stop moving but a reboot corrected it.

GPS modules have been around for many years. here's a screen shot using one hooked up to the com port of a computer installed in a 2001 SS camaro.
messages_0 (37).jpeg
 
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duanra

Active Member
Dec 14, 2018
1,321
814
Montreal
I'm interested in knowing how my car knows where it is on the map

I don't think there are GPS receivers so is it inertial navigation? Dead reckoning?

The reason I ask is that since my last update (2021.12.25.7) my car screen-map shows my car location sometimes blocks away from its actual location. Usually lasts only a few minutes but happens almost every day at the beginning of every drive. Happens both when navigating and just driving.

Also the screen will stutter/freeze for a few seconds when the location is incorrect.

I have re-booted numerous times. I have a service appointment scheduled but I wonder if anyone else is experiencing similar issues.
Very same issue. Lately, when i start, it takes the car a few minutes to figure out where it is. And I didn't add anything on the car.
 

Msjulie

Active Member
Jun 26, 2016
2,448
1,809
Monterey Peninsula
Another anecdotal bit of info - my car is 99.9% reliable telling me where it is, rarely if ever being confused, and accurate beyond my expectations. I'm assuming it's also using WiFi IP to zero in on home too.

The more issues I hear about 2021.12.25.7 the more I am resisting my car's attempts to install that version :(
 

Silicon Desert

Active Member
Oct 1, 2018
3,665
3,735
Sparks, / GF1
I'm interested in knowing how my car knows where it is on the map

I don't think there are GPS receivers so is it inertial navigation? Dead reckoning?
dmurphy answered your question. I am curious why you think the car doesn't have a gps receiver in it? Lots of things have gps chips in them these days. Like your smart phone for example.
 

linux-works

Active Member
Dec 23, 2019
2,188
4,169
mtn view, ca
there is a thing called cold-start and warm-start for gps.

cold start can take 5 minutes to acq. the birds. (love calling them birds, sorry) ;)

warm start can begin in 10's of seconds or even less.

ideally, you keep gps 'warm' but that takes power. no one likes vampire drain. so its a balance.

there is also DR in the chipset; whether tesla enables it (or even if the vendor's code works...) I cant say. I cant say for other reasons, too (sorry).

but there is gps there and you are probably seeing a cold start long delay.

oh, gps can also crash, so the watchdog for that chip might have to restart it. not uncommon, sadly.
 

holmgang

Active Member
Sep 9, 2019
1,327
1,458
eu
you can see DR at work if youre driving through a long tunnel. car location starts to drift from the mapped road location, as its approximating your position. same thing happens with your phone.
 
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linux-works

Active Member
Dec 23, 2019
2,188
4,169
mtn view, ca
cars can supply other hints to the chip; wheel revolutions (hall effect sensors), wheel angle, IMU (usually inside gps module can) and of course rf based satellite gps. as all that streams in to the chip and some gets interrupted, some corrupted, some jittered, the chip has to fuse (yes, that again) all that and make sense of it, as an uninterrupted output that the thing downstream of it, will consume (and depend on).

when you buy an amazon/ebay gps module for $5, you are not getting this (fancy DR stuff).

you need to sign nda and get unlock code to unlock vendor extras, like DR. and you get vendor support. you'll need it, too, lol.

and its hard to get working. which is why its not just a simple little thing that Just Plain Works. it will be a while, still.

and there are higher res forms of gps (various kinds of assist); but the fusion is still the tricky part, imho.
 
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NedH

Member
Feb 27, 2019
154
154
GA
cars can supply other hints to the chip; wheel revolutions (hall effect sensors), wheel angle, IMU (usually inside gps module can) and of course rf based satellite gps. as all that streams in to the chip and some gets interrupted, some corrupted, some jittered, the chip has to fuse (yes, that again) all that and make sense of it, as an uninterrupted output that the thing downstream of it, will consume (and depend on).

when you buy an amazon/ebay gps module for $5, you are not getting this (fancy DR stuff).

you need to sign nda and get unlock code to unlock vendor extras, like DR. and you get vendor support. you'll need it, too, lol.

and its hard to get working. which is why its not just a simple little thing that Just Plain Works. it will be a while, still.

and there are higher res forms of gps (various kinds of assist); but the fusion is still the tricky part, imho.
Thanks for the GPS info.

But since I never had these issues before the two downloads. do you have any idea why the GPS would suddenly start having these problems after a software update? (Remember that the last two updates failed to install completely until a second download--related? GPS module issue?)
 

Proflig8tor

Member
Jun 23, 2019
93
135
Marietta, GA
There may be service issues affecting GPS. Weather and our own friendly government can degrade the system. Pilots have to check coverage when GPS is used for terminal area operations & approaches. Avionics have Predictive Receiver Autonomous Integrity Monitoring (PRAIM) and I'd bet Tesla has that information buried somewhere in it's software. Parking in a concrete or metal structure could negatively affect reception on start. Our house has a concrete composite siding which isn't real GPS friendly.

It is also quite likely that Tesla uses a sensor that aggregates from many GPS like sources. There is also GLONASS, BeiDou, Galileo. All these used together is called GNSS.

The Tesla GPS works really well in our experience.
 

duanra

Active Member
Dec 14, 2018
1,321
814
Montreal
There may be service issues affecting GPS. Weather and our own friendly government can degrade the system. Pilots have to check coverage when GPS is used for terminal area operations & approaches. Avionics have Predictive Receiver Autonomous Integrity Monitoring (PRAIM) and I'd bet Tesla has that information buried somewhere in it's software. Parking in a concrete or metal structure could negatively affect reception on start. Our house has a concrete composite siding which isn't real GPS friendly.

It is also quite likely that Tesla uses a sensor that aggregates from many GPS like sources. There is also GLONASS, BeiDou, Galileo. All these used together is called GNSS.

The Tesla GPS works really well in our experience.
Well if the plane's gps I fly had the same reliability than the one I have in my 3. I'll be dead ! These day, when I start the car, it puts me about 3 km of my position and it takes a few km to give a proper indication.
The mobile service came but it didn't solve the issue.
 

linux-works

Active Member
Dec 23, 2019
2,188
4,169
mtn view, ca
Thanks for the GPS info.

But since I never had these issues before the two downloads. do you have any idea why the GPS would suddenly start having these problems after a software update? (Remember that the last two updates failed to install completely until a second download--related? GPS module issue?)
software updates can (and often do) have 3rd party drivers. one part of a driver is internal firmware for the gps unit. (what is inside the gps units are often intel or other cpus, sometimes even a VM inside! its wild; I've been able to ssh INTO the little metal can module on the pcb, even as root (with custom vendor firmware) to help debug some issues.

vendors are updating their gps, wifi, lte, ble firmware and the car vendor has to try integrating it, maybe even changing how they talk to the chip (metal can module).

I'll confess: sometimes those cans go to sleep and dont wake up. firmware on the car has to reboot them or reset them. its a race every few versions, where the car maker and the chip maker meet, discuss how to fix the issues and try things, then meet again next week.

and so, any update could have some new instrumented or test fw for the chips or modules. and some of the module design is so bad, the car company has to work around so many bugs; and many workarounds just dont work.

dont ask how I know (not really a lol, either)
 

linux-works

Active Member
Dec 23, 2019
2,188
4,169
mtn view, ca
Well if the plane's gps I fly had the same reliability than the one I have in my 3. I'll be dead ! These day, when I start the car, it puts me about 3 km of my position and it takes a few km to give a proper indication.
The mobile service came but it didn't solve the issue.
you dont need dead reckoning in aircraft. not that I know of, anyway. the job of gps in air is a lot easier and you also dont have multipath reflections like buildings are to cars.

and the fw in the gps on the plane has probably been the same tested version that the plane shipped with, and no reason to change what works.

DR in a car is 1000% more complex and its not easy to get working.

and the os around the gps chips, or rather the way the apps deal with it is often not very optimal. code quality of apps is generally low (in the field) and inside the metal cans, its generally a harder problem and takes more specialized skills, but the vendors are falling down on this (one big one in particular) and so that limits the quality; nothing can really be better than the metal can module, itself and if that has fundamental issues, you really cant fix them; you can patch around them, at best.

and I'll also say this; there seems to be more thought about safety for aircraft than landcraft.
 

duanra

Active Member
Dec 14, 2018
1,321
814
Montreal
you dont need dead reckoning in aircraft. not that I know of, anyway. the job of gps in air is a lot easier and you also dont have multipath reflections like buildings are to cars.

and the fw in the gps on the plane has probably been the same tested version that the plane shipped with, and no reason to change what works.

DR in a car is 1000% more complex and its not easy to get working.

and the os around the gps chips, or rather the way the apps deal with it is often not very optimal. code quality of apps is generally low (in the field) and inside the metal cans, its generally a harder problem and takes more specialized skills, but the vendors are falling down on this (one big one in particular) and so that limits the quality; nothing can really be better than the metal can module, itself and if that has fundamental issues, you really cant fix them; you can patch around them, at best.

and I'll also say this; there seems to be more thought about safety for aircraft than landcraft.
Yes, you have a point.
I am just a bit disappointed since the 1st 2 years, the gps was working flawlessly, and now it is not so reliable.
 

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