Making regular GPS ultra-precise(norwegianscitechnews.com)
norwegianscitechnews.com
Making regular GPS ultra-precise
https://norwegianscitechnews.com/2025/10/making-regular-gps-ultra-precise/
67 comments
Fun thing (?), I was excited on my last trip to Japan so I could test QZSS with my Pixel 9a, that supports it, and my GPS experience in urban canyons, specially in Shibuya, was terribly bad.
Even when in GPS Test or GPS Lock tools it was showing better than 3 meter horizontal accuracy, and a multitude of locked satellites, including some QZSS, the location would usually be 30 to 50 meters away. The first days I though I had lost all my capacity to navigate Tokyo, then I noticed the GPS was gas-lightning me.
I tried removing the phone case, changing GPS settings... and I had no luck.
Even when in GPS Test or GPS Lock tools it was showing better than 3 meter horizontal accuracy, and a multitude of locked satellites, including some QZSS, the location would usually be 30 to 50 meters away. The first days I though I had lost all my capacity to navigate Tokyo, then I noticed the GPS was gas-lightning me.
I tried removing the phone case, changing GPS settings... and I had no luck.
Extra satellites only have the potential to help a little bit in urban environments by increasing the odds of having a satellite directly overhead. Dense urban environments will have high multipath(longer time for signal to get to the receiver due to bouncing off buildings) which causes the position to be inaccurate.
They hand waved over a lot of it. The improvements in the urban canyon are not coming from GPS, but from things like wifi and 3d mapping, probably including cellular triangulations.
> The Quasi-Zenith Satellite System (QZSS) (Japanese: 準天頂衛星システム, Hepburn: juntenchō eisei shisutemu), also known as Michibiki (みちびき, "guidance"), is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (GPS) in the Asia-Oceania regions, with a focus on Japan.
https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System
https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System
Using building geometry to correct gnss signals is new.
I recall Uber looking into this around 8 years ago? Don’t know if it went past a publication.
Yep, they also used 3D building data for correcting position in urban canyons: https://www.uber.com/blog/rethinking-gps/
It ready mostly like an advertisement for Google's API.
Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower?
It is absolutely insane to me that Japan would be trying to economize using Molniya orbits or geosynchronous orbits in 2025.
Some BOTE math:
There are ~40k square degrees in a sphere. If I'm in a dead-end alley in an urban canyon and I have access to a 40 degree by 100 degree viewshed of sky (~4000 square degrees), that's 10% of the sky. Surface area of a 900km sphere is ~10 million square kilometers, 10% of that is 1 million square kilometers, Earth's radius is ~6400km, the orbital radius at 1000km is ~7400km, surface area of a 7400km radius sphere is ~700 million square kilometers, 1 million / 700 million ~= 1/700. Fly 3500 birds and you'll on average see five of them at a time in a 40 by 100 degree viewshed. But you'll have such a large angular parallax between their positions, and so little of the ionosphere in the way, that you get extremely high accuracy.
...
Many countries have their own SBAS to correct for ionospheric ephemera using a combination of regional ground stations and low flying satellites - The US calls their WAAS, Europe uses EGNOS, Japan uses MSAS, Russia and China have versions for their respective constellations, etc.
QZSS is a related but distinct idea that poses a little more like a localized addition to the GPS constellation.
It is absolutely insane to me that Japan would be trying to economize using Molniya orbits or geosynchronous orbits in 2025.
Some BOTE math:
There are ~40k square degrees in a sphere. If I'm in a dead-end alley in an urban canyon and I have access to a 40 degree by 100 degree viewshed of sky (~4000 square degrees), that's 10% of the sky. Surface area of a 900km sphere is ~10 million square kilometers, 10% of that is 1 million square kilometers, Earth's radius is ~6400km, the orbital radius at 1000km is ~7400km, surface area of a 7400km radius sphere is ~700 million square kilometers, 1 million / 700 million ~= 1/700. Fly 3500 birds and you'll on average see five of them at a time in a 40 by 100 degree viewshed. But you'll have such a large angular parallax between their positions, and so little of the ionosphere in the way, that you get extremely high accuracy.
...
Many countries have their own SBAS to correct for ionospheric ephemera using a combination of regional ground stations and low flying satellites - The US calls their WAAS, Europe uses EGNOS, Japan uses MSAS, Russia and China have versions for their respective constellations, etc.
QZSS is a related but distinct idea that poses a little more like a localized addition to the GPS constellation.
There are efforts on building LEO PNT (Low Earth Orbit Position Navigation Timing) constellations. I just really really hope it wont be a private company like SpaceX that operates it, having GPS and later the other GNSS constellations available for free have been essential for a lot of use cases.
https://www.esa.int/Applications/Satellite_navigation/LEO-PN...
https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt
https://www.xonaspace.com/
https://www.esa.int/Applications/Satellite_navigation/LEO-PN...
https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt
https://www.xonaspace.com/
> Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower?
For the record, block III GPS satellites are 3880kg. A Starlink satellite is 800kg. But I don't know how much of the GPS satellites' weight is a necessity due to the atomic clocks they carry. Either way the constellation would be at least a bit smaller due to launch costs.
For the record, block III GPS satellites are 3880kg. A Starlink satellite is 800kg. But I don't know how much of the GPS satellites' weight is a necessity due to the atomic clocks they carry. Either way the constellation would be at least a bit smaller due to launch costs.
Precision GPS is useful for a lot of things, but not for safety. Until we equip every deer, child, and pavement heave with a GPS saying exactly where it is cars will need "something" else to detect hazards. That GPS needs to be 100% reliable, even though we cannot predict when a child will attempt to run outside naked (without their GPS position transmitter), or the pavement will decide to fail (presumably without updating the GPS).
Prevision GPS is useful for a lot of things, but it isn't needed for car navigation. If you know within 100 meters of where you are you can figure out the exact lane you are in by other clues - clues that you need to look for anyway because road/utility crews will sometimes direct you to do things that are not on your updated maps.
I couldn't read the rest of the article because that navigation bugged me too much.
Prevision GPS is useful for a lot of things, but it isn't needed for car navigation. If you know within 100 meters of where you are you can figure out the exact lane you are in by other clues - clues that you need to look for anyway because road/utility crews will sometimes direct you to do things that are not on your updated maps.
I couldn't read the rest of the article because that navigation bugged me too much.
I don't get it.
I can see how precision GPS is not required for safety, and how it is not sufficient for safety, but can you elaborate on why reducing noise in this signal is not even useful?
I can see how precision GPS is not required for safety, and how it is not sufficient for safety, but can you elaborate on why reducing noise in this signal is not even useful?
Just reread this and realized I probably didn't answer the question as you meant to ask it.
If you read close you said GPS is not helpful for safety, but I didn't say it was useless for other purposes.
When you are in a car you are only rarely in a situation where it is even possible for you to be on a different road than what the GPS says. Which is more likely, a car is driving through the fence around my yard, or driving on the road. For navigation it is almost always good enough to assume you are on the one road that it is legal to travel on that is within the error bars. Only in a few cases is there a "frontage road" where there are two options that you can't be sure of which one you are on. In other cases where you cannot be sure you will quickly have moved far enough along the road that the other choice isn't viable anymore.
For lane-level navigation this precision isn't as helpful as you might expect because you can never be sure if your maps are correct. So your navigation systems needs to take other inputs which will sometimes discover the map is incorrect/out of date.
It might be helpful in weather events where the road is completely ice covered - but those are also situations where GPS signals are most likely to be obscured (via cloud cover) and so again you need somethings.
Still if you have more data it can be helpful. However it is only helpful when you can handle it being wrong.
If you read close you said GPS is not helpful for safety, but I didn't say it was useless for other purposes.
When you are in a car you are only rarely in a situation where it is even possible for you to be on a different road than what the GPS says. Which is more likely, a car is driving through the fence around my yard, or driving on the road. For navigation it is almost always good enough to assume you are on the one road that it is legal to travel on that is within the error bars. Only in a few cases is there a "frontage road" where there are two options that you can't be sure of which one you are on. In other cases where you cannot be sure you will quickly have moved far enough along the road that the other choice isn't viable anymore.
For lane-level navigation this precision isn't as helpful as you might expect because you can never be sure if your maps are correct. So your navigation systems needs to take other inputs which will sometimes discover the map is incorrect/out of date.
It might be helpful in weather events where the road is completely ice covered - but those are also situations where GPS signals are most likely to be obscured (via cloud cover) and so again you need somethings.
Still if you have more data it can be helpful. However it is only helpful when you can handle it being wrong.
Disagree with your take about how much you can trust the GPS. Maybe on a sparse road network this may be the case, but on a dense road network, stacked roads with adjacent lanes (like on a highway interchange )it can be downright wrong, even after corrections. But like you said in those cases we would have to rely on other inputs to compute precuse lane level location.
It isn't useful because you need those other things anyway and so it becomes excess data that you don't need. It can still be nice to know which lane you are in, but you have to be able to work 100% without that information, or worse then the information you have is wrong. (that is they just changed the pattern of the intersection and so you no longer can use the second from the left lane to turn)
If/when QPS is realized, calibration to a fixed point via manual verification, fixed base station(s), and/or multiple GNSS systems then GNSS spoofing, accuracy, and precision won't matter all that much because it will be entirely self-contained.
It's absurd overkill to put GNSS transmitters, RFID tags, and/or Bluetooth beacons on every object because the world is being flooded, for better or worse, with AI visual and IR cameras.
> Prevision GPS is useful for a lot of things, but it isn't needed for car navigation. If you know within 100 meters of where you are you can figure out the exact lane you are in by other clues - clues that you need to look for anyway because road/utility crews will sometimes direct you to do things that are not on your updated maps.
Except it is because driving direction routing depends on determination is based upon knowing which of several parallel, different roads one is on like the difference between being on a highway and on a parallel frontage road. Incorrect road detection leads to offering wrong directions.
It's absurd overkill to put GNSS transmitters, RFID tags, and/or Bluetooth beacons on every object because the world is being flooded, for better or worse, with AI visual and IR cameras.
> Prevision GPS is useful for a lot of things, but it isn't needed for car navigation. If you know within 100 meters of where you are you can figure out the exact lane you are in by other clues - clues that you need to look for anyway because road/utility crews will sometimes direct you to do things that are not on your updated maps.
Except it is because driving direction routing depends on determination is based upon knowing which of several parallel, different roads one is on like the difference between being on a highway and on a parallel frontage road. Incorrect road detection leads to offering wrong directions.
The things people do to avoid building trains and cycle paths.
The social norm that we seem to be slowly stumbling into assumes a different state of affairs:
That the roadways ought to always be clear of anything but cars which are behaving normally, and that if you can keep a car in the lane then anything unusual which happens isn't the car driver's fault.
Debris, animals, children, pedestrians, cyclists, motorcycles, stopped cars, construction workers and their vehicles, and anything else in our complex world that may find its way into the road - these aren't visible to someone blinded by oncoming headlights at night, they don't register in the same way as a car in the peripheral vision of someone looking at their cell phone or touchscreen controls, they may not be detected by radar cruise sensors or lane centering cameras, they certainly won't register on a GPS navigation track...and in a collision, society increasingly blames the thing that wasn't ~~supposed to be there~~ *anticipated* to be there rather than the driver which crashed into the thing.
I recognize that the likely cause of this is simply the infrequency of those events. Spend a few thousand miles seeing little other than cars on the road, and it's easier for your brain to assume that cars are the only thing that can be on the road. But my skeptical, cynical, conspiracy-minded side wonders if some of this trend is encouraged by submarine marketing efforts from self-driving vendors - the problem gets a lot easier when your "autonomous" vehicle isn't at fault for hitting a pedestrian in the road and you can just follow a GPS track while sensing for 5000 lbs steel boxes following the same GPS track.
That the roadways ought to always be clear of anything but cars which are behaving normally, and that if you can keep a car in the lane then anything unusual which happens isn't the car driver's fault.
Debris, animals, children, pedestrians, cyclists, motorcycles, stopped cars, construction workers and their vehicles, and anything else in our complex world that may find its way into the road - these aren't visible to someone blinded by oncoming headlights at night, they don't register in the same way as a car in the peripheral vision of someone looking at their cell phone or touchscreen controls, they may not be detected by radar cruise sensors or lane centering cameras, they certainly won't register on a GPS navigation track...and in a collision, society increasingly blames the thing that wasn't ~~supposed to be there~~ *anticipated* to be there rather than the driver which crashed into the thing.
I recognize that the likely cause of this is simply the infrequency of those events. Spend a few thousand miles seeing little other than cars on the road, and it's easier for your brain to assume that cars are the only thing that can be on the road. But my skeptical, cynical, conspiracy-minded side wonders if some of this trend is encouraged by submarine marketing efforts from self-driving vendors - the problem gets a lot easier when your "autonomous" vehicle isn't at fault for hitting a pedestrian in the road and you can just follow a GPS track while sensing for 5000 lbs steel boxes following the same GPS track.
The likely cause of this is the depersonalization of people at the behest of technology.
Why don’t cities have ground beacons for this?
Much cheaper than satellites and would be guaranteed to see heavy use
Much cheaper than satellites and would be guaranteed to see heavy use
Some places have free RTK networks their citizens can use. Michigan's department of transportation, for instance, runs a CORS network that anyone can request access to. (At least as far as I can tell. The signup form doesn't ask for affiliation or payment.) It's just distributed over the internet, the assumption being that you probably have internet access already.
One of these days I'll figure out how to set up a free NTRIP caster on my Galmon station so it can do double-duty. The trick then is advertising and discovery.
It would be lovely to have, say, a standard wifi SSID or a standard LORA channel that your local corrections network would broadcast on. That way you could have a large number of client devices not each needing their own internet access SIM card or whatever. I wonder if the corrections stream would fit into an FM RDS payload or something.
Trouble is, there's so much money in the L-band corrections services, and so little money in replacing them for free...
Oh, yeah, the cryptocurrency folks have weighed in, there's a thing called "goodnet" which appears to be microtransactions in exchange for NTRIP streams over some medium. I haven't looked further into it.
One of these days I'll figure out how to set up a free NTRIP caster on my Galmon station so it can do double-duty. The trick then is advertising and discovery.
It would be lovely to have, say, a standard wifi SSID or a standard LORA channel that your local corrections network would broadcast on. That way you could have a large number of client devices not each needing their own internet access SIM card or whatever. I wonder if the corrections stream would fit into an FM RDS payload or something.
Trouble is, there's so much money in the L-band corrections services, and so little money in replacing them for free...
Oh, yeah, the cryptocurrency folks have weighed in, there's a thing called "goodnet" which appears to be microtransactions in exchange for NTRIP streams over some medium. I haven't looked further into it.
Thanks - that's a lot of good info :)
Sparkfun page suggests one can do some of these adjustments via software too:
https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all
>1 cm accuracy is also possible with a few lower cost receivers (such as the NEO-M8T) by capturing raw streams from the GPS satellites and then post processing the logs with an open source program called RTKLIB.
Sparkfun page suggests one can do some of these adjustments via software too:
https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all
>1 cm accuracy is also possible with a few lower cost receivers (such as the NEO-M8T) by capturing raw streams from the GPS satellites and then post processing the logs with an open source program called RTKLIB.
Post-processing is wild. Lots of detail here: https://rtkexplorer.com/
There are even cheaper raw-data receivers, this one is popular among Galmon stations: https://www.aliexpress.us/item/2251832630341954.html
There are even cheaper raw-data receivers, this one is popular among Galmon stations: https://www.aliexpress.us/item/2251832630341954.html
While we're at it, could we also broadcast navigation map updates via that FM stream?
Why over a special radio system? Why not over the internet?
Why a special wifi? Why not just multicast streaming over the internet?
So you can deploy a bazillion devices without each one needing internet access, which typically has a cost because there's administrative overhead to handling abuse complaints, etc, that come along with full internet access.
If all you got was a one-way stream of data with no internet access (assume your CORS virtual station location is the AP's location, so no need to even pick your own mountpoint) then the abuse potential is basically nil. Just like with FM RDS and stuff, it's just a broadcast that you receive, you can't do anything bad with it. It's not internet, it's just one-way data. Difference being that a lot of microcontrollers now have wifi MAC/PHY built in, whereas FM would need more silicon.
If all you got was a one-way stream of data with no internet access (assume your CORS virtual station location is the AP's location, so no need to even pick your own mountpoint) then the abuse potential is basically nil. Just like with FM RDS and stuff, it's just a broadcast that you receive, you can't do anything bad with it. It's not internet, it's just one-way data. Difference being that a lot of microcontrollers now have wifi MAC/PHY built in, whereas FM would need more silicon.
Advertising and discovery: rtk2go.com or similar. Public casters.
GPS beacons would be stupidly expensive, as you'd need tens of thousands of them per city, and each one of them would need a very accurate atomic clock.
It would make far more sense (but still unviable) to go for Eurobalise-style RFID tags embedded in the road surface.
It would make far more sense (but still unviable) to go for Eurobalise-style RFID tags embedded in the road surface.
>you'd need tens of thousands of them per city
I was thinking more find a tall building and throw a single one there. Or maybe tallest 3.
As I understand it even a small number of extra satellites with line of sight can improve results a fair bit.
So aiming at low hanging fruit rather than blanket city
>very accurate atomic clock.
Indeed, but I'd think managing that on ground is easier than in space.
I was thinking more find a tall building and throw a single one there. Or maybe tallest 3.
As I understand it even a small number of extra satellites with line of sight can improve results a fair bit.
So aiming at low hanging fruit rather than blanket city
>very accurate atomic clock.
Indeed, but I'd think managing that on ground is easier than in space.
What happens when the building sways multiple feet in the wind? We don't normally think about them moving, but for accurate positioning I'd think the additional distance to the beacon could be a problem.
no, you arn't understanding. Those beacons would just be fixed places that know what their position is according to the GPS network.
You're tihnking of someone tkaing a GPS sattilite and putting it somewhere.
You're tihnking of someone tkaing a GPS sattilite and putting it somewhere.
That's kinda what RTK does, you have a ground station and transfer correction data for the visible satellites from it to your GNSS receiver. It doesn't transmit a GNSS signal itself but functionally the effect is vaguely comparable to a "satellite on the ground", without interfering on the actual signals.
The newest TV broadcast standard (ATSC 3.0) does include positioning information which is far, far, far harder to jam than GPS signals.
https://www.nab.org/bps/
https://www.nab.org/bps/
As with all things ATSC 3, the question becomes that while it is possible... a) is it actually enabled on stations?, b) is it DRM encumbered?, c) is it patent encumbered?
5G has fairly sophisticated positioning support, especially in the latest releases. Base stations generally are in precisely known locations and have good timebases. Urban locations which are challenging for gnss usually have good 5G coverage
https://www.ericsson.com/en/blog/2024/11/5g-advanced-positio...
https://www.ericsson.com/en/blog/2024/11/5g-advanced-positio...
Nextnav (no affiliation) is trying to do something similar. https://nextnav.com/
Edit: not affiliated with the company
Edit: not affiliated with the company
There's no need with hybrid positioning in cellular location chipsets that use cell towers, one or more GNSS constellations, and/or a WiFi SSID GIS database (like Skyhook).
RTK = Trimble Navigation.
Even back in 1999 prior to Selective Availability (SA) zeroing[0], fixed base station-assisted (pre-WAAS DGPS RTK) could achieve 10 mm horizontal accuracy and 1 m vertical accuracy. It was good enough that farming, mining (above ground), and earth-moving equipment could combine 2 receivers to determine tool angle and cut depth.
0. SA was an injected random error for security reasons that was constant for a local area, so it was weak security because it could be easily defeated if a fixed base station's position was known by subtracting it in the RTK receiver via DGPS update.
Even back in 1999 prior to Selective Availability (SA) zeroing[0], fixed base station-assisted (pre-WAAS DGPS RTK) could achieve 10 mm horizontal accuracy and 1 m vertical accuracy. It was good enough that farming, mining (above ground), and earth-moving equipment could combine 2 receivers to determine tool angle and cut depth.
0. SA was an injected random error for security reasons that was constant for a local area, so it was weak security because it could be easily defeated if a fixed base station's position was known by subtracting it in the RTK receiver via DGPS update.
I had some experience with RTK and sensor fusion about 13 years ago on a college project. At the time the only people that were using RTK in real world applications were tractor companies because it kind of matters that you're precise when seed drilling. I'm not sure how far RTK has come but it had pit falls back then like base station drift when the set of satellites it saw changed due to them going over the horizon.
Tractors don't go _that_ fast but I'm not sure I'd rely on it in an actual car for anything but slightly better GPS.
Tractors don't go _that_ fast but I'm not sure I'd rely on it in an actual car for anything but slightly better GPS.
There is decent RTK coverage in the US these days: https://e38surveysolutions.com/pages/ntrip-rtk-network-acces...
Galileo HAS allows precision down to 30cm with enough integration time. Without additional external data.
For free.
Receivers slowly hitting the market now - a year ago this was only receivable by SDR-driven devices.
For free.
Receivers slowly hitting the market now - a year ago this was only receivable by SDR-driven devices.
"with enough integration time" — the article is about live navigation, which generally can't afford that.
With SBAS 1-2m precision can be done easily in the US and EU. Most of the time enough for any navigational use.
Pretty much all GPS/Galileo receivers are able to receive and decode these overlays.
Pretty much all GPS/Galileo receivers are able to receive and decode these overlays.
You can get integration time while driving. You combine accelerometer and gyroscope data to cancel out movement effects.
That's a classic use-case of Kalman
That's not so good. 24-channel GPS can do <1cm today while moving (that's RTK) using (free in most areas) WAAS. Fusion constellation many channel GNSS receivers with clear terrain can do about as good without DGPS (of which RTK is a subset). There's really no reason not to use as many constellations and as many satellites as possible to reduce error more quickly.
I really hope QPS works, becomes available to the public, and decreases in cost quickly because it would make GNSSes more of a backup and calibration system than a primary system. Hybrid location chipsets in mobile handsets use a fusion of many technologies and techniques which would be really cool to have QPS especially for underground metro systems and inside buildings with lots of signal-attenuating materials.
I really hope QPS works, becomes available to the public, and decreases in cost quickly because it would make GNSSes more of a backup and calibration system than a primary system. Hybrid location chipsets in mobile handsets use a fusion of many technologies and techniques which would be really cool to have QPS especially for underground metro systems and inside buildings with lots of signal-attenuating materials.
Don't cars also measure their wheel movements to increase location accuracy?
Yup! Otherwise your navigation would become totally useless the second you entered a tunnel.
Dead reckoning can get quite accurate once you realise that cars drive on roads, so if you have a reasonably up-to-date map you can use turns and corners to "snap" back to the road and reset a good bunch of your accumulated error.
Dead reckoning can get quite accurate once you realise that cars drive on roads, so if you have a reasonably up-to-date map you can use turns and corners to "snap" back to the road and reset a good bunch of your accumulated error.
Almost, they use accelerometers and gyros, 'dead reckoning' is the keyword to look for. The wheels are a bit unreliable because the diameter changes slightly with pressure and temperature.
Wheels are still used for legal telemetry: speedometer and odometer.
The legal requirements on that (in most places) are that the speedometer is in something like a -0%/+10% range, i.e. never shows lower than you're actually driving. Not only is that not helpful for navigation (but you could compensate that/shift the error window), but the precision is also pretty low (which you can't easily compensate).
(There are two precision problems here — tyre diameter changes slighly while you're driving, but also it's not precise to begin with before you even turn on the car, due to tyre wear.)
You'd need to do something like calibrating wheel speed data while you have good GNSS reception, then you could use it for dead reckoning. But accelerometers and gyros are cheap…
P.S.: I didn't say wheel speed data isn't used, just that it wouldn't be precise enough on its own.
(There are two precision problems here — tyre diameter changes slighly while you're driving, but also it's not precise to begin with before you even turn on the car, due to tyre wear.)
You'd need to do something like calibrating wheel speed data while you have good GNSS reception, then you could use it for dead reckoning. But accelerometers and gyros are cheap…
P.S.: I didn't say wheel speed data isn't used, just that it wouldn't be precise enough on its own.
Are there modern cheap IMUs that are able to hold position for some time available?
My understanding is that using plain accelerometers and gyros will drift quite soon due to noise, while some cars (e.g. Tesla) maintain their position quite well when doing to an underground parking structure and then coming back. So I actually do believe that they put a lot of weight to tracking wheels, which I believe would not accumulate that much error. (For more precise location they'd still need to use accelerometers to detect downhill/uphill, though.)
So I believe that the precision actually favors wheels, not IMUs.
In the underground parking case it doesn't actually matter too much if there's a certain % offset, because you're very likely driving a near-closed loop of some sort; and as you say, the wheel size ratio can be calibrated upon good GNSS data.
My understanding is that using plain accelerometers and gyros will drift quite soon due to noise, while some cars (e.g. Tesla) maintain their position quite well when doing to an underground parking structure and then coming back. So I actually do believe that they put a lot of weight to tracking wheels, which I believe would not accumulate that much error. (For more precise location they'd still need to use accelerometers to detect downhill/uphill, though.)
So I believe that the precision actually favors wheels, not IMUs.
In the underground parking case it doesn't actually matter too much if there's a certain % offset, because you're very likely driving a near-closed loop of some sort; and as you say, the wheel size ratio can be calibrated upon good GNSS data.
yeah Phones have pretty good IMUs. the TLDR is you combine accelerometers and gyros (preferably a bunch of them to minimize error) with GPS which gives you pretty accurate position and can also give you velocity data with some tricks)
But if you don't have GPS, then you don't have a high-confidence low-precision absolute position input to your system? Whereas with wheels you already get a lot of data about that when they are not turning at all.
A friend tried to make a phone ruler app (using IMU) and the experience was that it didn't take very long for the distance to shoot to the horizon. So, thought I should try how this kind of solution would work with the hardware of today, but it turns out there seem to be zero such apps in the Play Store.. The tools of that category all seem to use a camera.
I think the lack of these tools is a testament to the approach not really working.
A friend tried to make a phone ruler app (using IMU) and the experience was that it didn't take very long for the distance to shoot to the horizon. So, thought I should try how this kind of solution would work with the hardware of today, but it turns out there seem to be zero such apps in the Play Store.. The tools of that category all seem to use a camera.
I think the lack of these tools is a testament to the approach not really working.
This type of solution works better at large scale where you have space and power budget for a lot more IMUs. Phones are very power and space constrained, so you only have room for 1-2 IMUs. In a car, 10W isn't a problem and there's plenty of room for higher power and higher quality sensors.
Another option to get more precise positioning is to switch from GPS to Galileo.
Galileo generally offers better civilian accuracy than GPS because it uses modern signal structures with better resistance to multipath and interference and provides dual-frequency signals (E1 + E5) to all users, which mitigates ionospheric errors.
Galileo generally offers better civilian accuracy than GPS because it uses modern signal structures with better resistance to multipath and interference and provides dual-frequency signals (E1 + E5) to all users, which mitigates ionospheric errors.
most software now uses multiple GNSS at the same time?
Usually cheaper GPS modules only do one band (L1), though. But using multiple constellations still helps a lot.
Also, RTK is the opposite of "regular" GPS, it's generally considered a "special" usage mode of GPS.
And discussing urban canyons with no mention of QZSS?