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Why Digital Maps Are Inaccurate in China
- _greim_ 11y agoInteresting. Why can't maps be produced using satellite photos?
- jackvalentine 11y agoThe problem isn't of producing a map, it's of publishing it. If you go ahead and do that be prepared to find yourself locked out of anything to do with China.
- _greim_ 11y agoBut if the bottleneck is publication, not data gathering, then why does the Chinese government bother cracking down on map making activities? > Three British geology students discovered this the hard way while “collecting data” on a 2009 field trip...
- jackvalentine 11y agoBecause I was responding to your "why can't they be done with satellite photos?"
- est 11y ago> then why does the Chinese government bother cracking down on map making activities Most China polices can be explained by the "fuck you" treatment. What is "fuck you" treatment? Well fuck you go figure it out yourself.
- b6 11y agoSee also: "no why". Paranoid psychopaths are so obsessed with keeping a stranglehold on every possible thing that they design algorithms to screw up maps, causing untold problems, inconvenience, extra costs, incompatibility, etc. It's reverse-engineered and compensated for by everyone else, but they just keep doing it. Why? No why. #china. My cynicism is, I think, my way of dealing with heartbrokenness.
- wongarsu 11y agoFor large companies or government the bottleneck is publication. Most individuals don't care about repercussions from a foreign country and could publish with little practical problems, but those people don't have access to spy satellites.
- coldtea 11y ago>then why does the Chinese government bother cracking down on map making activities? Try collecting map data as a foreigner in the US (or most countries for that matter), and you'll find out, especially if you go anywhere near sensitive facilities.
- tristanj 11y agoTopic discussed 1 month ago (205 points) here: https://news.ycombinator.com/item?id=10964450 https://news.ycombinator.com/item?id=10964450
- est 11y agoin case anyone missed, the source code of evil transform between WGS-84 and GCJ-02 in C/C#/Go/Javascript/Python/PHP/Swift https://github.com/googollee/eviltransform https://github.com/googollee/eviltransform
- contingencies 11y agoI was dealing with multi-source map authoring with coordinate system conversions here in China years ago (~2004)... that's before Google Maps came out. Later I found that in China a given city's satellite data for a will be off by some standard drift, usually pretty much effectively constant for a whole city area, and by co-relating a few known points throughout your area of interest across multiple sources' coordinate systems you can scale things well, even if you are remaining 100% projection agnostic (black box treatment). I have never studied computational cartography, GIS and only have a basic self-taught understanding of matrices but didn't find this all that difficult to hack up at the time. We were using it to generate little point-of-interest area maps to help people find locations throughout the city on a sort of city-focused whats on style magazine operation. Maps were generated in multiple languages. We were shut down by the publishing bureau but subsequently kept running anyway, apparently with no problems. The business continues today, though I have nothing to do with it.
- zcbenz 11y agoThere is a Chinese idiom describing things like this: Plugging One's Ears While Stealing a Bell.
- ovis 11y agoThe article implies that the source of trouble is the GCJ-02 datum. Is this really such a major problem though? In North America, both the NAD27 and NAD83 datums are still common. NAD83 nearly matches WGS84, but NAD27 can be quite off. Datum transformation is a well understood topic, so what's so special about China?
- HillRat 11y agoYes, this. I've had to deal with inter-datum conversions in the past, and as far as I can tell, though after a very brief review, GCJ-02 is just another datum, albeit one not well documented. The "random offset" described in various documents may be easily explained by the datum being optimized for accuracy in a relatively small area, and thus errors increase as you expand your mapped area. (For those who don't speak GIS, datums are essentially a way of mapping an orange peel to a table; because any attempt to dedimensionalize points on a sphere must by necessity introduce errors, datums are designed to either minimize that error in all locations -- which is what WGS84 does -- or to gain greater accuracy by focusing on a smaller part of the globe, such as the "state plane" datums. When you see misaligned points on maps that derive data from various sources, it's usually a good idea to make sure that multiple unconverted datums aren't the source of the problem.)
- maxerickson 11y agoThe state plane coordinate systems use NAD27 or NAD83 (plus improvements). https://en.wikipedia.org/wiki/State_Plane_Coordinate_System https://en.wikipedia.org/wiki/State_Plane_Coordinate_System The flattening of an orange peel you mention is more about projection, a datum is a mathematical description of the earth that maps out how geographic coordinates will vary. Given geographic coordinates, a projection system is needed to display them on a flat surface (or really any surface that doesn't match the shape of the geographic coordinate system). Differences between datums do arise from different modeling choices and should be accounted for when translating coordinates, but as the fine article discusses, the offsets in GCJ-02 are algorithmic and are not a refinement of WGS84, they obscure true location. https://en.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China#GCJ-02 https://en.wikipedia.org/wiki/Restrictions_on_geographic_dat...
- jzwinck 11y agoSouth Korea also has problems with Google Maps. And also for political reasons. Apparently they have some disagreement with Google which prohibits Maps from supporting routing aka navigation. It also prohibits full resolution display, although the map data is basically present. It seems to be a way to retain control over what is undoubtedly economically valuable information. But at what cost?
- coldtea 11y ago>It seems to be a way to retain control over what is undoubtedly economically valuable information. But at what cost? At the cost of not giving up some of your national assets such as geographic info just to get better GPS gadgets from foreign companies? They can still create and enjoy their own maps and tools.
- tylerpachal 11y agoI was in Korea for awhile and never really noticed too much of a problem with GMaps. Do you know if Naver Maps is better?
- ck2 11y agoWe like to think of North Korea as the crazy country but we forget it has a much older brother who is far more dangerous because it appears to be mature and acceptable yet is almost as nuts.
- coldtea 11y agoSaid the country that evaporated 250.000 Japanese (men, women and children), sprayed Vietnam farmers with chemicals, had segregation until the sixties, has the biggest number of incarcerations in the world, has been tens of times at war with places thousands of miles away from its borders, has supported all kinds of dictatorships abroad as long as they have been favorable for its interests, had 2 open occupations of foreign countries just until a few years ago, is full of religious nuts, has a huge surveillance system that spans the whole world, its police kills more people (mostly blacks) in a year that the rest of the Western world combined does in 10, and has elected Bush for two terms, while now half of it celebrates Trump...
- leesalminen 11y agoOh no you didn't!
- digi_owl 11y agoIts funny how some of the most paranoid seeming nations on the planet has within the last 100 years or so experienced foreign military meddling in internal affairs.