Making regular GPS ultra-precise
norwegianscitechnews.com
norwegianscitechnews.com
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?
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.
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.
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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.
https://www.esa.int/Applications/Satellite_navigation/LEO-PN...
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.
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 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?
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.
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.
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.
Much cheaper than satellites and would be guaranteed to see heavy use
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.
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.
There are even cheaper raw-data receivers, this one is popular among Galmon stations: https://www.aliexpress.us/item/2251832630341954.html
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.
It would make far more sense (but still unviable) to go for Eurobalise-style RFID tags embedded in the road surface.
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.
You're tihnking of someone tkaing a GPS sattilite and putting it somewhere.
https://www.ericsson.com/en/blog/2024/11/5g-advanced-positio...
Edit: not affiliated with the company
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.
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.
For free.
Receivers slowly hitting the market now - a year ago this was only receivable by SDR-driven devices.
Pretty much all GPS/Galileo receivers are able to receive and decode these overlays.
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.
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.
(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.
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.
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.
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.