[HN Gopher] Making regular GPS ultra-precise
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Making regular GPS ultra-precise
Author : giuliomagnifico
Score : 58 points
Date : 2025-10-07 12:54 UTC (6 days ago)
(HTM) web link (norwegianscitechnews.com)
(TXT) w3m dump (norwegianscitechnews.com)
| Tepix wrote:
| 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.
| ktosobcy wrote:
| most software now uses multiple GNSS at the same time?
| Podrod wrote:
| Yeah, according to the 'GPS Test' Android app my phone is
| picking up and using GNSS signals from GPS, Galileo, GLOSNAS,
| and Beidou sats.
| UltraSane wrote:
| Man I remember getting my first GPS receiver in the 90s and
| now are phones can use so many sats.
| geerlingguy wrote:
| Usually cheaper GPS modules only do one band (L1), though.
| But using multiple constellations still helps a lot.
| Havoc wrote:
| Why don't cities have ground beacons for this?
|
| Much cheaper than satellites and would be guaranteed to see heavy
| use
| eqvinox wrote:
| 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.
| myself248 wrote:
| 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.
| bitbckt wrote:
| Do you mean GEODNET?
| myself248 wrote:
| Oops, indeed I do.
| crote wrote:
| While we're at it, could we also broadcast navigation map
| updates via that FM stream?
| chillingeffect wrote:
| Why over a special radio system? Why not over the internet?
| Havoc wrote:
| 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.
| myself248 wrote:
| 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
| chillingeffect wrote:
| Why a special wifi? Why not just multicast streaming over the
| internet?
| myself248 wrote:
| 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.
| BenjiWiebe wrote:
| Advertising and discovery: rtk2go.com or similar. Public
| casters.
| crote wrote:
| 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.
| Luc wrote:
| https://en.wikipedia.org/wiki/Eurobalise Cool.
| Havoc wrote:
| >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.
| cyanydeez wrote:
| 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.
| auspiv wrote:
| 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/
| toast0 wrote:
| 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?
| burnt-resistor wrote:
| 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).
| zokier wrote:
| 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...
| bjacobt wrote:
| Nextnav (no affiliation) is trying to do something similar.
| https://nextnav.com/
|
| Edit: not affiliated with the company
| eqvinox wrote:
| 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?
| tecleandor wrote:
| 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.
| jlack wrote:
| 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.
| cyanydeez wrote:
| 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.
| leecb wrote:
| > The Quasi-Zenith Satellite System (QZSS) (Japanese: Zhun Tian
| Ding Wei Xing shisutemu, Hepburn: juntencho eisei shisutemu),
| also known as Michibiki (michibiki, "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
| sampton wrote:
| Using building geometry to correct gnss signals is new.
| addaon wrote:
| I recall Uber looking into this around 8 years ago? Don't
| know if it went past a publication.
| mapt wrote:
| 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.
| sorenjan wrote:
| 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/
| cyanydeez wrote:
| It ready mostly like an advertisement for Google's API.
| mavhc wrote:
| Don't cars also measure their wheel movements to increase
| location accuracy?
| eqvinox wrote:
| 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.
| willis936 wrote:
| Wheels are still used for legal telemetry: speedometer and
| odometer.
| eqvinox wrote:
| 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.
| _flux wrote:
| 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.
| adgjlsfhk1 wrote:
| 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)
| _flux wrote:
| 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.
| crote wrote:
| 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.
| NoiseBert69 wrote:
| 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.
| eqvinox wrote:
| "with enough integration time" -- the article is about live
| navigation, which generally can't afford that.
| NoiseBert69 wrote:
| 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.
| adgjlsfhk1 wrote:
| You can get integration time while driving. You combine
| accelerometer and gyroscope data to cancel out movement
| effects.
| burnt-resistor wrote:
| 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.
| bluGill wrote:
| 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.
| LeifCarrotson wrote:
| 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.
| cyanydeez wrote:
| The likely cause of this is the depersonalization of people
| at the behest of technology.
| burnt-resistor wrote:
| 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.
| brookst wrote:
| 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?
| bluGill wrote:
| 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)
| bluGill wrote:
| 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.
| andrepd wrote:
| The things people do to avoid building trains and cycle paths.
| TYPE_FASTER wrote:
| There is decent RTK coverage in the US these days:
| https://e38surveysolutions.com/pages/ntrip-rtk-network-acces...
| burnt-resistor wrote:
| 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.
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