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Making regular GPS ultra-precise

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Re: Making regular GPS ultra-precise

#41

Post by _flux »

eqvinox wrote: post #13
willis936 wrote: post #10

Earlier quoted context omitted.

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'…

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.

Re: Making regular GPS ultra-precise

#42

Post by Havoc »

crote wrote: post #20
Havoc wrote: post #3

Why don’t cities have ground beacons for this? Much cheaper than satellites and would be guaranteed to see heavy use

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.

>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.

Re: Making regular GPS ultra-precise

#43

Post by bluGill »

brookst wrote: post #37
bluGill wrote: post #23

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 up…

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?

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)

Re: Making regular GPS ultra-precise

#44

Post by mapt »

eqvinox wrote: post #6

Nothing in this article is new, and the problem with RTK has always been the (unpaid) availability of reference stations. Good on them for trying to make a package of it, but maybe this "news" site could've used a bit less unchecked enthusiasm. 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?

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.

Re: Making regular GPS ultra-precise

#45

Post by toast0 »

auspiv wrote: post #29
Havoc wrote: post #3

Why don’t cities have ground beacons for this? Much cheaper than satellites and would be guaranteed to see heavy use

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/

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?

Re: Making regular GPS ultra-precise

#46

Post by zokier »

Havoc wrote: post #3

Why don’t cities have ground beacons for this? Much cheaper than satellites and would be guaranteed to see heavy use

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...

Re: Making regular GPS ultra-precise

#47

Post by bluGill »

brookst wrote: post #37
bluGill wrote: post #23

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 up…

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?

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.

Re: Making regular GPS ultra-precise

#48

Post by sorenjan »

mapt wrote: post #44
eqvinox wrote: post #6

Nothing in this article is new, and the problem with RTK has always been the (unpaid) availability of reference stations. Good on them for trying to make a package of it, but maybe this "news" site could've used a bit less unchecked enthusiasm. 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?

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 i…

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/

Re: Making regular GPS ultra-precise

#49

Post by adgjlsfhk1 »

eqvinox wrote: post #15
NoiseBert69 wrote: post #14

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.

"with enough integration time" — the article is about live navigation, which generally can't afford that.

You can get integration time while driving. You combine accelerometer and gyroscope data to cancel out movement effects.

Re: Making regular GPS ultra-precise

#50

Post by addaon »

sampton wrote: post #39
eqvinox wrote: post #6

Nothing in this article is new, and the problem with RTK has always been the (unpaid) availability of reference stations. Good on them for trying to make a package of it, but maybe this "news" site could've used a bit less unchecked enthusiasm. 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?

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.
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