Another strange thing I found that might not be super well known (I didn't know about it) is that all GPS data in China is offset by a nonlinear psuedo-random amount. If you turn on the satellite view in Google Maps and look at various cities in China, you'll see that the road and business overlay is off by anywhere from 50m to 500m. And the strangest thing is that it's not a consistent offset from place to place.
Turns out this is very intentional, and China uses a different geographic coordinate system than the rest of the world. WGS-84 is the most common coordinate system, but China uses GCJ-02, sometimes called Mars Coordinates. Part of GCJ-02 is an algorithm that obfuscates the results. So applying any GCJ-02 coordinate to a globe using WGS-84 coordinates gets distorted like a funhouse mirror.
It's easy to find open source libraries to convert WGS-84 to GCJ-02 and vice versa. But Google Maps doesn't do it, for political reasons I suppose? I've read that if you open Google Maps within China the mapping data is correct, but have no way to test that.
The open-sourced implementation one may find on the internet are probably thru sth like curve fitting by sampling many data points. It may have good enough approximations but may not work one day if the gov agency decides to change the algorithm. Changing algorithm is a backward compatibility hell but not a big problem for the industry actually, because most Map apps are owned by big corp which has resource and motivation to comply.
Such irony in CCP using licensing to protect their IP
and what's the "correct-conception"?
I'm curious because I get what parent means in terms of intellectual property issues in China but I don't get what do you mean from your comment, especially the fact that you include "other party states" - is it some sort of general rule that you're hinting at?
 funny, I just realised that there is no antonym of "misconception"
At least in science education, misconceptions are so vastly more common than correct conceptions, that it makes sense there's a compact negative form but not a positive one. /s
china, the ethnicity, is indeed thousands years old. CCP, however, is barely over 70 yrs old.
But the CCP has been controlling mainland China for a little bit over 70 years, indeed.
At the end of the day they may obfuscate coordinates and blur maps, but the truth will eventually come out.
Can't imagine why anyone would want that to happen.....
Let's see... Wikipedia seems to confirm:
> During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; this was discontinued on May 1, 2000 by a law signed by President Bill Clinton.
Private, independent geographical surveying is illegal in China.  So technically you can't do it even in the local coordinate system.
But OSM actually doesn’t use that system! They use the normal coordinate system, which makes them unique across mapping services (and also a good tool to use to RE geojson away from chinas system).
FYI: And even far outside of them too
" It is an Inertial Guidance System with an additional Star-Sighting system (this combination is known as astro-inertial guidance), which is used to correct small position and velocity errors that result from launch condition uncertainties due to errors in the submarine navigation system and errors that may have accumulated in the guidance system during the flight due to imperfect instrument calibration. GPS has been used on some test flights but is assumed not to be available for a real mission. "
Tomahawk missiles are also fed a navigation package before launch which allows them to navigate without additional signals (I'm sure accuracy goes up if they do have GPS available). I believe it's something akin to terrain maps that it can use to navigate to it's target.
I would argue that any nation that is reliant on those public networks to be effective are going to lose within minutes of an actual conflict.
I believe it's already established that the Russians are capable of completely blocking out GPS signals.
So no, I don't think we'd be facing mutually assured destruction.
Now the impact on civilian life if some nation decided to start the space wars? Catastrophic. We'd basically block off space for the next 100 years because of deadly debris in orbit :/
The problem with defending a satellite is the missile really only needs to get kinda close. And yeah, relativistic speeds and distances in space are huge, but I would find it hard to believe we could defend our satellites in any meaningful way against a nation-state level threat.
I suspect you could go hours driving round a city with the GPS and WiFi location turned off before losing your position - simple wheel speed, gyro and compass is sufficient for most stuff.
I suspect the most accurate measurements would be done using wideband SDR, iff I were able to acquire absolute position references for the signals I was seeing. Not likely, especially for something I might like to let others play with and/or generalize.
Everywhere I read about the subject the general consensus is that using accelerometer and gyro data from the average phone is a fool's errand. I have zero experience with the field so I wouldn't know if failure was incorrect signal processing or just had sensors.
With a particle filter and enough computation, that error can be eliminated after the fact. Ie. At the time you won't know where you are, but after you get out of the metro and the particle filter reconverged you'll know where you were with more accuracy at some point in the past.
They make external GPS units that plug into your car and connect to your phone wirelessly for example Garmin GLO that are supposed to improve accuracy although I haven't used one myself and thus can't vouch for it.
Only the former would match the car's odometer, of course.
I think the US Government can also shut it off at a moments notice.
Modern dirt cheap receivers can pick up European, Chinese, Russian, etc. constellations for location just as well as the American one.
The other benefit is when doing PPP the convergence time is dramatically shorter with multi constellation.
When doing RTK most receivers will use only GPS, as it is generally the most accurate, but it can and will use GLONASS occasionally. I have never seen one use beidu or Galileo
I briefely looked through the pdf, and probally missed it?
I live in the Bay Area, and homeowners are concerned over a few inches.
(There's a huge need for cheap surveys. Until GPS gets it to under a inch, traditional surveys will off pipes, and landmarks, is here to stay? Or, am I wrong?)
The problem for homeowners is that surveys aren't enough. The vast majority of land titles are not registered in precise coordinates; they're registered in terms of landmarks, benchmarks, and so forth. This is changing at a glacial pace, but for now, the tech isn't the problem.
I spent 2 months cycling China from Hong Kong to Beijing. Despite only using Chinese characters, Baidu maps worked very well for me. I copied the characters I needed (Hotel, supermarket) into it from the translator.
Here's my journal
There are cheaper places where only locals can go (and till some years ago, also the other way around was true)
A lot of countries use their own coordinate systems, that make their countries look flat on a x/y plane. Eg. my country - slovenia.
Usually those coordinate systems are easy to calculate to wgs84 or web mercator projection, compared to the chinese solution
edit: updated silly question after reading more on this
Does that mean:
1) My GPS module also gives out obfuscated coordinates when in China or
2) Google uses shifted satellite images?
more here: https://news.ycombinator.com/item?id=10964450
robotastronaut also corrected me that it's not actually the GPS that is being obfuscated, but the map coordinate system. So your GPS device is probably receiving correct results, but on an improperly projected map.
The opposite is true: If you look at areas like the Macau-Zhuhai border or Hong Kong-Shenzhen, you'll see that the satellite imagery is continuous but the mapping data has discontinuities at the border (some zhuhai streets are halfway across the water to Macau!)
I can use OpenStreetMap fine in China. But that's not Chinese data.
If a Chinese person sends me a location marker on WeChat, the marker will show up (for me, in WeChat) at some other, unintended, location; I can't use that feature at all.
Yes, Israel specifically has favor from the US government that satellite imagery of that country is allowed to be blurred:
Naver Maps has really good street view and very accurate maps in SK.
Turn-by-turn navigation also doesn't work using Google Maps. Meanwhile SK navigation apps like Naver Maps or Kakao Maps have really poor navigation features if you compare to what you'd have using Google Maps on an American road.
The end result is that consumers suffer, since artificial market protection leads to an inferior product and no real need to improve and compete by players on the local market.
>Why is Google’s Korean map behaving this way? In short, because of Korea’s Spatial Data Industry Promotion Act from 2009, specifically Article 7, which states that:
>Spatial data business operators may produce and distribute any processed spatial data. In such cases, processed spatial data shall not include any spatial data on any military base provided for in subparagraph 1 of Article 2 of the Protection of Military Bases and Installations Act nor on any military installation provided for in subparagraph 2 of the said Article.
>And considering the existence of the most heavily militarized border on the planet between North Korea and South Korea, this means a substantial part of South Korea is riddled with military installations.
>By limiting the maximum resolution of its Korean imagery on maps.google.co.kr, Google appears to have satisfied Korean regulators that it is obeying the relevant Korean laws. Thus, Google avoids having to blur or otherwise censor the satellite imagery base layer for Korea — something which it has successfully managed to avoid in China, India and elsewhere.
Write up about Apples courser application
Or whoever is in charge of importing the data simply doesn’t know that different coordinate systems is a thing. You’d be surprised how many GIS professionals are oblivious to this, especially ones in charge of things that tend to spill large amounts of oil into the environment when they get it wrong: https://www.maritime-executive.com/article/london-club-warni...
https://goo.gl/maps/oDwCuGhxxZVSj7nJ6 Hong Kong/China border bridges
Why would a space agency use a coordinate system to obfuscate results on another planet?
FYI: Google has never really quit China. It has running offices in Beijing, Foshan, and, recently, Shenzhen.