"Currently, WAAS satellite coverage is only available in North America"
RTK is probably more available than people think. My state offers a public network of continuously-operating reference stations; you can sign up for a free account and then do whatever RTK madness you desire. https://cors.dot.ny.gov/ if you happen to be in New York.
(I realize now that I really wanted to reply to the person complaining about not being in North America, but oh well, maybe they'll find this.)
It's amazing what you can do with consumer-priced gear these days. I set up a Sparkfun ZED-F9P breakout board as a fixed beacon on my roof, and then their "RTK Facet" as the rover to do precise measurements to create a map. I could have done the basic thing I needed to by hiring a surveyor or eyeballing things with a tape measure, but this is much more general.
The GNSS software world seems to be a mess though, ripe for a paradigm shift. For example, QGIS seems to be based on flat projections with transformations rather than 3d-native - from what I can tell, QGIS seems to consider the "degree" to be a unit of length measurement! This leads to ridiculous things like being able to accidentally measure a nonsensical "cartesian" distance between two points that differs from the actual distance by a factor dependent on latitude.
I've still got to tidy up my own pipeline that lets me do things like turn N (point, distance) samples into a single point. I would have thought that type of operation would be common, but thinking about how surveyors work I guess they're usually locating points optically, rather than trying to position a GPS receiver at the point to be measured.
Another thing you might find interesting is that you can generate a report on how good your reference station is. It's actually in Sparkfun's documentation, so you're probably aware, but if not: https://learn.sparkfun.com/tutorials/how-to-build-a-diy-gnss... Specifically the part where you collect data with u-center and upload the results to https://webapp.csrs-scrs.nrcan-rncan.gc.ca/geod/tools-outils... for analysis was very interesting.
Imagine you go on a road trip (along the surface of the earth). How far have you driven? In spherical coordinates, that's just changing two angles. In Cartesian coordinates, it's an ugly mess. Doesn't hurt that it's a lot easier to measure angles in surveying than distance.
However, certain GIS systems like QGIS and arcGIS are designed for making maps and have to display things in a 2D space. Thus, they have a projection mapping the spherical coordinates to Cartesian canvas coordinates and back again. This leads to unintuitive behavior, but it's mathematically hard to do better.
Now, the user interfaces and the terminology and the subtly disastrous inconsistencies between different data sources? Hot flaming garbage, all of it. These aren't problems with the underlying data models though.
Actually no, I'm complaining about the exact opposite. I want to be working in spherical native coordinates, but QGIS seems to treat "degrees" as just another fixed unit of length measurement rather than an angular measurement!
For example I had the measurement projection set to "cartesian", which I would have expected to either give me the linear distance from (X,Y,Z) to (X,Y,Z), or the linear distance between the projection of those two points on an approximation of the earth's surface (either sphere or ellipsoid). Instead, it was treating (Lat, Lon) as if they were (X,Y) coordinates on a flat map and doing Pythagorean theorem on the angular measurements, resulting in the longitudinal distance being off by a factor of cos(latitude) !
I can see no paradigm in which such a result would ever be desired, apart from QGIS fundamentally working in terms of linearized projections, with WGS84 coordinates being added on as an afterthought.
We already have premium high resolution GPS. Its for military use only.
Extra precision can be achieved with fixed-point augmentation signals, which I believe is common at airports and construction sites. I would assume the at militaries similarly augment signals in theaters of war. But that’s different than some separate high-resolution mode.
At this point, so many civilian services depend on the high-resolution data that I’d be pretty surprised to see GPS going back to a two-tier system.
A citation for the above:
“In May 2000, at the direction of President Bill Clinton, the U.S. government ended its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.
“The United States has no intent to ever use Selective Availability again.”
What the US government did was remove the bias from the CA code so it could be used for precise positioning. The military still uses P codes as well. I believe there is a small gain to be had but it’s due to frequencies.
Since then there have been several more advances, mostly to broadcast local augmentation signals. Wide Area (WAAS) and Ground Bases (GBAS) are common in receivers.
L5 is a new band to help solve multipath error in urban areas.
Most receivers also have remote autonomous integrity monitoring, where it can predict its own area of probability (by using groupings of 4 in 5 satellites), and if it’s too large for the intended use case, alert the user. Also with 6 satellites it can calculate combinations of 5 satellite groupings to work out (and exclude) faulty satellites. This is Fault Detection & Exclusion (FDE).
Mobile devices will also download their own separate high resolution almanac and ionospheric data over the internet which is superior to the low data rate GPS almanac. It can also use known cell locations to approximate its position. Combined, this enables rapid (hot) signal lock immediately onto the correct satellite code & Doppler shift frequency, which is why your mobile gets a fix in 3 seconds, versus your car which takes minutes.
The precision of positioning from the P code is 10 times greater than the C/A code (about 30cm vs 3m). This is due to the wavelength/'chip length' of the code signal which is modulated onto the carrier wave (10.23 Mhz / 29.31 m wavelength for P code, 1.023 Mhz / 293.1 m wavelength for C/A code). Positioning precision is limited to about ~1% of the chip length by signal processing.
https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...
So what, throw down an RTK pod and now you have like centimeter level accuracy. That's stuff anyone can buy for COTS drones, I'm eyeing on it for my DJI drones.
The only thing needing realtime in-flight accuracy of that level without an RTK pod is weaponry and maybe cars outside of road (because on road, they can augment GPS with camera data and road mappings).
Or maybe they'd just buy an exclusive contract.
Showing a clear lack of understanding how the US government works. The US military can't actually do this.
(After all, this is the same organization that's happy to pay out the nose to keep ULA alive to have redundant launch options.)
Given that we can get satellites to GEO, we can presumably get one that goes boom up there, should we be so inclined.
Also remember even if you did launch on liquid rockets, It is not easy to launch them in quick succession or with stealth. Liquid rockets needs a lot of time to load fuel, needs a ton of auxiliary equipment( cryogenic fuel storage at-least) and have limited shelf life once loaded which means they are limited to few known sites which you can quickly take offline after the first attack/launch.
Solid rockets/ICBMs can be launched from variety of platforms some of them very mobile and also given their lower footprint - Silos and other sites can be hidden and missiles moved around to retain the strike capability.
ASATs are primarily designed to target low flying spy sats[1], taking few key ones out can at the right time can potentially deliver few hours of advantage in a battle before alternative sats can be rerouted. Communication and navigation sats on the other hand are designed to operate even during normal times when few go offline without lose of operational capabilities .
[1] Also this is much easier to justify domestically and globally than say communication ones even if they were dual use.
but then they'd have to make it reliable. We are also not sure how much more (if at all) accurate it is.
sure the bandwidth of the downlink is much higher, and louder than GPS, but the accuracy of the clocks on the satellites is much less. More importantly they are not characterised, so we arn't sure how much they drift due to temperature (both from sun and other effects.)
depending on the navigation type, visual positioning might be better/faster/more accurate. For "military" purposes, silent autonomous navigation without radio sensors is pretty appealing. Using satellite imagery, its perfectly possible to make an accurate, robust visual navigation system
for urban areas, "VPS"s are far quicker and more accurate, but require network access to work practically.