7 ms·
Making regular GPS ultra-precise
- Tepix 1y agoAnother 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.
- ktosobcy 1y agomost software now uses multiple GNSS at the same time?
- Podrod 1y agoYeah, according to the 'GPS Test' Android app my phone is picking up and using GNSS signals from GPS, Galileo, GLOSNAS, and Beidou sats.
- UltraSane 1y agoMan I remember getting my first GPS receiver in the 90s and now are phones can use so many sats.
- geerlingguy 1y agoUsually cheaper GPS modules only do one band (L1), though. But using multiple constellations still helps a lot.
- Havoc 1y agoWhy don’t cities have ground beacons for this? Much cheaper than satellites and would be guaranteed to see heavy use
- eqvinox 1y agoThat'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.
- myself248 1y agoSome 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.
- eqvinox 1y agoNothing 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?
- tecleandor 1y agoFun 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.
- jlack 1y agoExtra 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.
- cyanydeez 1y agoThey 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.
- leecb 1y ago> 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
- mavhc 1y agoDon't cars also measure their wheel movements to increase location accuracy?
- eqvinox 1y agoAlmost, 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.
- willis936 1y agoWheels are still used for legal telemetry: speedometer and odometer.
- eqvinox 1y agoThe 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.
- _flux 1y agoAre 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.
- NoiseBert69 1y agoGalileo 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.
- eqvinox 1y ago"with enough integration time" — the article is about live navigation, which generally can't afford that.
- NoiseBert69 1y agoWith 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.
- adgjlsfhk1 1y agoYou can get integration time while driving. You combine accelerometer and gyroscope data to cancel out movement effects.
- NoiseBert69 1y agoThat's a classic use-case of Kalman
- burnt-resistor 1y agoThat'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.
- bluGill 1y agoPrecision 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.
- LeifCarrotson 1y agoThe 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.
- TYPE_FASTER 1y agoThere is decent RTK coverage in the US these days: https://e38surveysolutions.com/pages/ntrip-rtk-network-access-by-state?srsltid=AfmBOoruCU8GcZS_aoesstEzHToeaYF9mjGY367uv9RMypRD5KG4OKBr https://e38surveysolutions.com/pages/ntrip-rtk-network-acces...
- burnt-resistor 1y agoRTK = 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.
- stlava 1y agoI 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.
- Mary900 1y ago[flagged]