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Making regular GPS ultra-precise

norwegianscitechnews.com

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Re: Making regular GPS ultra-precise

#11

Post by myself248 »

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

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.

Re: Making regular GPS ultra-precise

#12

Post by UltraSane »

Podrod wrote: post #5
ktosobcy wrote: post #4

Earlier quoted context omitted.

most software now uses multiple GNSS at the same time?

Yeah, according to the 'GPS Test' Android app my phone is picking up and using GNSS signals from GPS, Galileo, GLOSNAS, and Beidou sats.

Man I remember getting my first GPS receiver in the 90s and now are phones can use so many sats.

Re: Making regular GPS ultra-precise

#13

Post by eqvinox »

willis936 wrote: post #10
eqvinox wrote: post #9

Earlier quoted context omitted.

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.

Re: Making regular GPS ultra-precise

#15

Post by eqvinox »

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.

Re: Making regular GPS ultra-precise

#16

Post by NoiseBert69 »

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.

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.

Re: Making regular GPS ultra-precise

#17

Post by bitbckt »

myself248 wrote: post #11
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

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 fr…

Do you mean GEODNET?

Re: Making regular GPS ultra-precise

#18

Post by tecleandor »

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?

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.

Re: Making regular GPS ultra-precise

#19

Post by crote »

mavhc wrote: post #8

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.

Re: Making regular GPS ultra-precise

#20

Post by crote »

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.

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