Why Digital Maps Are Inaccurate in China
travelandleisure.com
travelandleisure.com
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.
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.
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?
(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.)
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_dat...
[0]https://www.ordnancesurvey.co.uk/business-and-government/hel...
> Three British geology students discovered this the hard way while “collecting data” on a 2009 field trip...
Most China polices can be explained by the "fuck you" treatment. What is "fuck you" treatment? Well fuck you go figure it out yourself.
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.
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.