Even if I do a reset + cold start in u-center or similar, I still don't have to wait 12 minutes. I wonder why.

Almanac gives coarse satellite position information (and some other stuff), good enough to know which ones are probably visible and therefore prioritize signal acquisition attempts which used to be very very costly in terms of signal processing. That's the message that takes up 12.5 minutes to piece together. Nowadays you can just brute force all possible satellite signals and there's no need to wait around for the almanac information. Each satellite signal broadcasts precise satellite location information (ephemeris), which takes maybe 30 seconds to get a few frames I believe. So that's basically the bottleneck for a modern chipset which starts with zero information and relies solely on the GPS signals to navigate.

Classical GPS receivers use the almanac (and a reasonably accurate local clock) to determine which satellites are probably in view, and with which Doppler shifts. I would not be surprised if modern GPS chips had enough compute power to simply correlate the received signal with all gold codes and at all reasonable Doppler shifts. The almanac is then no longer necessary.

Usually that approach cuts the sync time by factor of ten, even if the real ephemeris diverges from the general almanac.

This is how they build RTK surveying equipment, and they can have their own RTK reference point that uses statistical averaging over time to get accuracy down to the centimeter range or below, and then rebroadcast that to the local RTK rover nodes. There are multiple correction systems available that you can subscribe to, some of which can transmit their corrections via 4G/LTE/5G or other radio band communications, so that you don't need your own RTK reference for your rover units.

For good RTK equipment, you can easily pay $40k or more, but if you look around you can find some equipment that costs less than $1000. My current favorite is the SparkFun GPS RTK Express Kit, although you need a pair of them if you want to do your own RTK reference point and you don't subscribe to one of the various other correction systems.

For RTK to be really useful for surveying a site, you need both the stationary reference unit and the Rovers.

I spent decades in high precision geophysical surveying using ground stations (fixed GPS recievers) and craft (aircraft | helicopters | etc) and it was common practice to collect data and post process ... merge airframe GPS data and ground station corrections in conjunction with other numerical corrections .. at the end of day.

For various forms of survey you really want to not transmit to|from your airframer "live" in any case - for EM | magnetic survey that's just another source of noise best dealt with by having everything not required switch off.

I concede the value for regular ground site survey tasks .. there's no downside to transmitting and applying corrections in real time - but it's not strictly required and for some forms of surveying it's preferable to record raw unaltered data and apply fixes later with the option of rolling back | examining the raw | etc.

But for the ground surveying and ground control RTK equipment I've been looking at, you do want to apply those corrections in real time. For example, if you're controlling a tractor that is pulling a lot of heavy equipment through a field of crops, and you want to make sure you line up correctly on the product being farmed (e.g., corn), you want to make sure that your tractor goes exactly where you want it to go, and in real time.

In my mind, that's what Real Time Kinetics is all about.

But yeah, real time control of moving vehicles is exactly where you want transmitted corrections - it originated with military requirements to correct in real time as interceptors close in on targets and today (like yourself?) I use it in the agricultural domain for tractors and drones.

But if you're taking actions that might result in changing the thing or the space you're surveying (like putting in markers, or controlling heavy equipment, or directing the application of military force), then that's where you will most likely want to have those real time corrections.

While the general orbits of the satellites (each is uniquely identifiable) can be pre-shipped, orbits do fluctuate, so the data would still need to be updated / fine tuned.

> The receiver is missing or has inaccurate estimates of its position, velocity, the time, or the visibility of any of the GPS satellites. As such, the receiver must systematically search for all possible satellites. After acquiring a satellite signal, the receiver can begin to obtain approximate information on all the other satellites, called the almanac. This almanac is transmitted repeatedly over 12.5 minutes. Almanac data can be received from any of the GPS satellites and is considered valid for up to 180 days.

* https://en.wikipedia.org/wiki/Time_to_first_fix

But a general fix can do done without any initial data, and is sped up by being near the previous last fix and caching some data.

[0] https://blog.brixit.nl/nitrokey-dissapoints-me/

Thought two: I've never considered how bizarre it is that GPS is an enormously expensive satellite constellation launched and maintained by the United States military that we make available for free to the entire world. As a US citizen I take it for granted - but it must be strange for someone to grow up in (for instance) Lebanon and use a GPS device.

I still remember my fascination with it when I got to use it for the first time, using a Garmin app on my Nokia 5800.

For good 30 years the strategy generally worked so much that satnav got synonymous with GPS.

Big players launched their own constellations anyway. GLONASS, Beidou and fledgling but accurate Galileo. And there are still more systems. So if GPS wasn't free manufacturers would use something else.

>After Korean Air Lines Flight 007, a Boeing 747 carrying 269 people, was shot down by a Soviet interceptor aircraft after straying in prohibited airspace because of navigational errors,[42] in the vicinity of Sakhalin and Moneron Islands, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good.

That's the neutral phrasing on Wikipedia. The actual announcement: https://www.reaganlibrary.gov/archives/speech/statement-depu...

>In their recent statements on the Korean Air Lines tragedy, senior Soviet officials have shocked the world by their assertion of the right to shoot down innocent civilian airliners which accidentally intrude into Soviet airspace. Despite the murder of 269 innocent victims, the Soviet Union is not prepared to recognize its obligations under international law to refrain from the use of force against civilian airliners. World opinion is united in its determination that this awful tragedy must not be repeated. As a contribution to the achievement of this objective, the President has determined that the United States is prepared to make available to civilian aircraft the facilities of its Global Positioning System when it becomes operational in 1988. This system will provide civilian airliners three-dimensional positional information.

Also, it would be disaster to lose GPS accuracy worldwide since so many users depend on it. It would also be pointless because there are other constellations like Galileo and GLOSNAS. Plus, multiband receivers are getting more common to support the new L5 signal.

GPS jamming and spoofing are more useful because they can be targeted to area. As is happening in Ukraine.

Anyway the point was that taxing receivers would be an option if they had wanted to finance the system, but for some reason they didn't, not so much to discuss this data storage tax to be paid out to the music industry

The tax is based on a quirk of copyright law designed by the media industry all the way back in the age of cassette recorders. Music companies realized that people were making copies of their songs from the radio for free (you could put together entire albums if you timed it correctly!) and from the cassettes they bought, and after some mess the "thuiskopie" (home copy) system was born.

Basically, you can make legal copies of any media you have legal access to as long as you pay the fee. This fee goes directly to on organisation (think MPAA but for all artists) which then redistributes the money according to Some Kind Of Model[1]. The fee is part of the sale of any digital or analogue container that can contain copyrighted works; it's a fixed price fee (https://www.thuiskopie.nl/nl/opgave/tarieven). Professionals who won't use their devices to store other people's work can get their money back if they fill in a form and send over the right paperwork, but let's be honest, nobody does this.

For a long time, the de facto interpretation of the thuiskopie law was that a copy you make for yourself (or your direct family/friends) at home is legal. That implied downloading MP3s and other files from the web was also legal [2]. Torrents involve sharing, so they were always off the table, but copies of torrented files given to family was treated like a legal copy. You could still be caught for piracy, but as long as someone else got you all of your pirated disks you were pretty much Technically Okay.

This interpretation was killed off when the media industry won a lawsuit against the government. It was always too good to be true, but it seemed to be one of the ways many pirates were appeased about this law. I'm pretty sure everyone considers this system to be stupid now that it's no longer a de facto piracy license. The copyright lobby is incredibly strong, though, so I doubt we'll see a change any time soon.

The copyright industry gets to charge you twice for the media you listen to. As long as this stupid system remains part of the law, I'm personally opposed to any subsidies for commercial media. If only a politician worth voting for actually cared about this crap...

[1]: Yes, this is legal, though I still don't know why.

[2]: Software has always been excluded from this, though; downloading software and games was never part of the deal, and software companies can't claim their take from the Thuiskopie system

In fact, in many countries pointing your SDR at 2G/3G/4G/5G frequencies is basically an instant felony, even without attempts to decrypt the traffic. If you get caught watching such traffic, you'll pay much more than just a small tax.

And in many other countries the "TV license" is just included in general tax; in e.g. when the TV license was abolished in the Netherlands taxes went up by 1.1% to compensate. In Germany it's €220/year/person (not household) regardless of whether you have a TV or not. This way you don't pay for a product I don't use.

To give another example, you used not to have to pay public broadcasting tax in Germany if you didn't have a TV or radio in your household. I would be highly amused to see you try to argue "it's just an electromagnetic radiation plotter, what do you mean tele, eh, vision?" to an unamused government official.

They could not put a special tax on receivers, let the manufacture and sale and commercial use of receivers create economic activity, and then tax that economic activity through, e.g., personal and corporate income tax, and use tht to fund the system.

The (hundreds of) millions spent on bonuses are nothing compared to the billions spent on making sure your doctor recommends UmbrellaCorp PainAWay™ over a generic brand that will cost you a tenth of the price [2]. That includes not just TV ads, but also buying conference tickets and free lunches for doctors; anything to make sure they get the upper hand.

[1]: https://www.csrxp.org/icymi-new-study-finds-big-pharma-spent...

[2]: It should be noted that some generics can work less effectively or cause additional side effects in some people, but for many types of medication the difference is minimal and sometimes the big-brand products even come with more side effects than their competitors' product

AFAIK originally the DoD weren't thinking of making GPS for public, just for military. Having these requirements would just make it extra complex, and unnecessary. First, it would require a lot of bandwidth, and then yeah, a bottleneck for how many receivers can be deployed, and it could take a lot of seconds until a unit finds a matching key to decrypt. Imagine a soldier needing to wait for her equipment to get the key to find her location while in a firefight...

[0] https://en.wikipedia.org/wiki/Global_Positioning_System

GPS is, at this point, a public good. Almost everyone uses it, and it’s central to current technology. It seems clear to me, at least, that it should be funded through general taxation, not some kind of user fee.

[0] https://en.wikipedia.org/wiki/Global_Positioning_System

GPS in combat debuted during the Gulf War, but mostly as a backup for navigation rather than targeting. We did not have 100% coverage back then, all of the satellites were not up yet.

IOC was defined as always being in sight of 3 or more satellites, plus maintenance capability. That was achieved in 1993.

Modern ICBMs use GNSS. Historically, they didn’t. Certainly not when the GPS constellation was deployed.

Do they? The US hasn't deployed a new generation of ICBMs since the GPS constellation became operational. I would also expect that plans for nuclear war wouldn't rely on vulnerable satellites remaining operational.

I thought that US weapons used GPS guidance as a low-cost alternative to other guidance methods in forgiving environments that don't have electronic warfare countermeasures (e.g. fighting the Taliban or armed forces equipped with old gear).

Both of these techniques are still good for removing much of GPS's error, which mostly involve the uncertainty about the "speed of light". It changes locally as the total electron content of the ionosphere changes. Measure against a reference station or between two different radio frequencies (L1/L2C), and that error can be minimized. You don't need a reference station anymore, as things like WAAS try to transmit these corrections from a satellite.

If you want to play with high-precisions GPS, you can easily buy fancy u-blox modules from Sparkfun, connect them to a Windows computer running uCenter (from ublox), and get access to reference stations through your state to do full DGPS. With good sky conditions, you should be able to move your receiver a few centimeters and watch the lat/lon change accordingly. (New York State's service is here: https://cors.dot.ny.gov/. It's free! They use a software suite that's designed to charge customers money for using the data, but the prices are all set to $0.)

People say that the achievement of the 20th century was the Internet, but I think GPS was a lot harder. The Internet is just computers connected to each other with cables! This is atomic clocks in space sending you messages indistinguishable from noise that let you find your position in space within a centimeter. When the aliens invade, I think they'll be impressed! I am, anyway.

As for difficulty, both are achievements and don’t undersell the difficulty of networking. At the 500ft level it’s all just wires but the actual details of doing it are incredibly difficult. It’s just that we’ve had so much experience pushing it forward that there’s a lot we can just take for granted which removes the magic from it.

https://www.allaboutcircuits.com/news/ethernet-turns-50-look...

And that’s just local area networking. Networking broad area networks is even more complicated.

As for people calling it the achievement of the 20th century, it’s more because of how it made the world smaller and the network effects of the changes it’s wrought to society (and from that perspective it is bigger than GPS and the computer itself).

https://www.spaceforce.mil/About-Us/Fact-Sheets/Article/2197...