GPS location and mapping errors compared to the real world

Arjen

Arjen

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Found on Anastasia Bizyayeva's Medium.com:
medium.com

Every map of China is wrong

And this is intentional…
medium.com medium.com
China GPS shift problem.

This naturally piqued my interest — I didn’t know Chinese geospatial data would be any different from the rest of the world. Hadn’t this been one of the few areas where we all agreed about the right way to do things?

The more I delved into this topic, the more interesting stuff I found, and the more it made sense from a Chinese perspective. So I thought I’d share the story here. We’ll cover the following:

  • The divergence between street view and satellite view in China
  • Why do Chinese maps look so odd compared to the rest of the world?
  • Why does the Chinese government want to have a different system?
  • Is there any way you can accurately map China?
  • What this means for the world

The divergence between street view and satellite view in China​

If you’ve never looked at a digital map of China, I urge you to do it now — initially, if you look at the street view, it looks like any other map you’ve encountered. However, if you overlay the satellite view you can see things are out of whack.
[...]
GPS uses the World Geodesic Standard 1984 (or WGS-84) as its reference standard. The National Geospatial Intelligence Agency (NGA) in the U.S. maintains WGS-84. This means that de facto, most of the world has subscribed to American mapping conventions.

There are a few countries that have established their own geodesic data, including Russia and China. China’s datum is called GCJ-02, which translates to ‘Topographic map non-linear confidentiality algorithm’ (the name ‘GCJ’ comes from the Chinese ‘guó-cè-jú’).

Here’s where it gets interesting — GCJ-02 is based on WGS-84, but with a deliberate obfuscation algorithm applied to it. The effect of this is that there are random offsets added to both latitude and longitude, ranging from as little as 50m to as much as 500m.
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More at the link.
 
Fascinating. And scary.
But surely we don't have to wait upon Chinese maps to build our own, right?
I'm pretty sure Western agencies have all mapped China very accurately from satellite observations for decades.
 
- A non-Chinese actor <edit> Everyone </edit> needs to cooperate with one of 14 Chinese companies for access to Chinese mapping data
- Chinese law forbids translating obfuscated mapping data to WGS-84
One more quote that might be of interest:
For any initiative that (1) needs international cooperation and (2) involves geospatial data, information reported out of China isn’t going to be entirely reliable, and if you’re working with geographic parameters that are only a few kilometres across, a potential difference of 500 metres in a coordinate can be pretty impactful. This ultimately means that data reported in GSJ-02 needs to be moderated in some way to account for inaccuracy, and individuals pursuing work in China will be penalised.
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I would imagine that avionics don't have the same problem that consumer products have.

Even where I work, truck drivers get misled as to where the warehouse is.
 
I mentioned this to a couple of my Chinese students, they mentioned the in car navigation system seems to work ok and seems accurate when in China (il try a wider poll)
 
TsrJoe said:
I mentioned this to a couple of my Chinese students, they mentioned the in car navigation system seems to work ok and seems accurate when in China (il try a wider poll)
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  • The Chinese state outlaws surveying and mapping activities of the nation to all but a handful of Chinese companies.
  • These companies and the state have accurate information about Chinese locations but apply a deliberate obfuscation algorithm on top of the international standard for all outside actors.
  • If a company wants Chinese location information, they have to partner with a Chinese company to get it, and it will have this obfuscation applied (as well as many locations hidden).
So long as you use a Chinese car navigation system from one of the permitted companies it should be accurate.
 
The real curiosity is why don't Western countries do this nowadays. Tactical fighter pilots the world over already rely on inputs from multiple GNSS systems to confound spoofing and REC, including Beidou and GLONASS, so having deliberate obfuscation algorithms seems a good idea to reduce the enemy's ability to leverage your own GNSS.

Archibald said:
This. The chinese government is pretty scary: authoritarian and paranoid.
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Si vis pacem, para bellum.

Stargazer said:
Fascinating. And scary.
But surely we don't have to wait upon Chinese maps to build our own, right?
I'm pretty sure Western agencies have all mapped China very accurately from satellite observations for decades.
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Probably, but by effectively double encrypting their own GNSS signal, they have made their electronic warfare job easier anyway. It beats export controls (ITAR), or degrading the signal (Selective Availability), as you can avoid needing to cut off the civilian market from high performance receivers in the first place.
 
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martinbayer said:
Perhaps because those countries are based on the concepts of freedom, openness, and democracy, and knowing that petty attempts of information suppression eventually will be futile and not win out?
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Do you mean to say that the U.S. should be sharing NGAD information openly with the Russians and PLAAF? They might want a heads-up.

Much like how BD-09 is censored "for improved user privacy" (and totally not to confound weapon employment) I guess Lockheed-Martin participates in "dangerous and illegal" activities (and totally not to confound weapon employment) too. Which is to say the U.S. does the same thing. Google and DOD have a pretty strong relationship behind closed doors.

DOD and its organs will tell Google to censor maps, so marking targets is hard(er) or so saboteurs can't destroy stockpiles, but it never actually bothers shifting the GPS coordinates so simply saturating the area with munitions after taking a picture with a imaging satellite (instead of an airplane) becomes more difficult.

It doesn't work for the PRC anymore, since there is publicly available code now, but it was quite clever for the mid-00's at a time the U.S. was loosening its restrictions on militarily relevant information. Evidently, the kind of paranoia that surrounds NGAD must be similar to the kind that surrounds BeiDou.

...or maybe the PRC's firms that handle GNSS data just found a way to make a quick buck by forcing "transfer algorithm" fees onto foreign investors instead of conforming to international standards?

Both could be true simultaneously but I want to believe the Soviet style of military planning is still alive somewhere.
 
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Because there are so many civilian applications that use GPS, from civil aviation and commercial logistics to recreation, that seriously obfuscating the GPS data would be a major hazard.

As far as BD-09 being obfuscated, that has almost zero military significance. The US armed forces aren't relying on Chinese maps or GNSS for targeting or guidance. We have our own GNSS and satellite mapping capabilities now, so it really doesn't matter that Chinese maps are wrong. This is unlike the Soviet era when we didn't have any way to reliably map a lot of their territory and needed to get hold of Soviet maps to figure out where stuff might be.
 
TomS said:
Because there are so many civilian applications that use GPS, from civil aviation and commercial logistics to recreation, that seriously obfuscating the GPS data would be a major hazard.
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Not if you do it so that you pull old receivers from the market and bring new ones in with sufficient lead time. Send fliers or something to people's houses, notify shipping firms, and offer rebates for turning in old receivers. There's not a huge second hand market of receivers.

It's more a question why wasn't it built in from the beginning, but I guess since Selective Availability did pretty much the same thing, it's a bit superfluous to stack obfuscation on top of that.

TomS said:
As far as BD-09 being obfuscated, that has almost zero military significance. The US armed forces aren't relying on Chinese maps or GNSS for targeting or guidance. We have our own GNSS and satellite mapping capabilities now, so it really doesn't matter that Chinese maps are wrong. This is unlike the Soviet era when we didn't have any way to reliably map a lot of their territory and needed to get hold of Soviet maps to figure out where stuff might be.
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Well, Chinese maps aren't "wrong" except when translated to WGS-84 so it only becomes an issue with commercial GPS receivers. All it really means nowadays is that using BeiDou for anti-spoofing would be a foolish move about 10 years ago, but now the obfuscation code is open source, so it's a bit irrelevant these days yeah.

That said if the U.S. is still relying solely on GPS, and not on multiple GNSS like Galileo/GLONASS/GPS which is world standard, that's odd.
 
Kat Tsun said:
Do you mean to say that the U.S. should be sharing NGAD information openly with the Russians and PLAAF? They might want a heads-up.

Much like how BD-09 is censored "for improved user privacy" (and totally not to confound weapon employment) I guess Lockheed-Martin participates in "dangerous and illegal" activities (and totally not to confound weapon employment) too. Which is to say the U.S. does the same thing. Google and DOD have a pretty strong relationship behind closed doors.

DOD and its organs will tell Google to censor maps, so marking targets is hard(er) or so saboteurs can't destroy stockpiles, but it never actually bothers shifting the GPS coordinates so simply saturating the area with munitions after taking a picture with a imaging satellite (instead of an airplane) becomes more difficult.

It doesn't work for the PRC anymore, since there is publicly available code now, but it was quite clever for the mid-00's at a time the U.S. was loosening its restrictions on militarily relevant information. Evidently, the kind of paranoia that surrounds NGAD must be similar to the kind that surrounds BeiDou.

...or maybe the PRC's firms that handle GNSS data just found a way to make a quick buck by forcing "transfer algorithm" fees onto foreign investors instead of conforming to international standards?

Both could be true simultaneously but I want to believe the Soviet style of military planning is still alive somewhere.
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So it sounds like one side (China) *is* distorting data while the other (USA) is *not* (i.e. "it never actually bothers shifting the GPS coordinates"), no? And *guessing* that LM might participate in "dangerous and illegal" activities is not really a very credible argument. Seems like you're not really seeing the forest for the trees, so to speak...
 
No asks about the Elephant in the room! When space is not owned by anyone and satellites are flying around the world, except for geo-stationary ones, shouldn't other countries be easily able to gather accurate mapping data on China anyway?
 
overscan (PaulMM) said:
So long as you use a Chinese car navigation system from one of the permitted companies it should be accurate.
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Which would mean the non-obfuscated data is there for the taking from any car in China that has a GPS.

It's either performative, done to satisfy someone who didn't understand the science, or groupthink. ETA: Or commercial.
 
DWG said:
Which would mean the non-obfuscated data is there for the taking from any car in China that has a GPS.
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Sure, if you drive around in a car with a WGS84 GPS system and a GCJ-02 GPS system, and compare the results of the two. That's a course of action which, I suspect, will earn you an extended stay with all expenses paid, courtesy of the Chinese government.
 
Yellow Palace said:
Sure, if you drive around in a car with a WGS84 GPS system and a GCJ-02 GPS system, and compare the results of the two. That's a course of action which, I suspect, will earn you an extended stay with all expenses paid, courtesy of the Chinese government.
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Not if you're doing it in the depths of Fort Meade or GCHQ or where-ever

You don't need to be on the spot to probe the database, you just need to tell it you are.
 
We do need to distinguish between deliberate obfuscation and cock-up. For instance the time I followed the GPS route to an aerospace company's site for an interview, and had it deliver me within 20m of their front gate, the only problem being the train tracks in a cutting between me and them.... (Good job I'd driven up to check the route the day before!)
 
Starting in the 1990s when GPS first became available to the public, my older brother picked up an in-car unit and began using it for his wanderings around the western Nevada hills (we had grown up in a family with a 1956 Jeep and a Father who loved "seeing where that old road went").

He also made a lot of trips on dirt roads etc in the course of his work - he worked for Sierra Pacific Power in their computer department, and they were converting isolated power transfer units to be controlled remotely via the main computer system.

He bought a GPS digital map pack from DeLorme (one of the pioneers of public-use GPS mapping)... but kept seeing that the GPS unit did not match the roads in the pack (they had been created from USGS maps, and were sometimes several miles off from reality).

So he contacted DeLorme, and their response was to send him a 4-antenna GPS mapping unit for his SUV (one antenna on each corner of the roof)* and a program for his laptop to record the readings and attach notes of where he went to compare with the readings, with his agreement to always leave it on when out of town (Reno, NV) and periodically send them his trip recordings with the location notes - so they could update and correct their map packs!

He did this for about 10 years, until incorrect locations had almost never showed up (thanks to both people like him and to DeLorme and the USGS having used satellite mapping to correct the databases the maps were created from).


* This reduced the error radius from hundreds of yards (for single units of the time) to less than 10 feet.
 
Truckers seem confused by GPS as to get to one of my two jobs.
Carto-Craft used to sell map-books of Jefferson county.
 
Amazon and Swift Transportation seem to suffer from GPS guiding them down roads not passable by their type of vehicle (box truck and semis). I'm talking 2-track jeep trails or similar.

And the since the drivers get fired if they don't follow the GPS exactly... (I'm thinking the drivers need to sue over the GPS endangering the drivers, some of the spots those trucks get sent could easily roll a semi or box truck)
 

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