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Does anybody know why, when you use Google Maps in China, your GPS location matches the map and not the satellite image? I would assume the maps being in GJC-02
by captainmuon 2y ago
Does anybody know why, when you use Google Maps in China, your GPS location matches the map and not the satellite image? I would assume the maps being in GJC-02 and the satellite images being in some other global coordinate system. So your position should line up with the imagery, not with the map. Does the GPS chip report modified coordinates when it detects it is in china? Or does Google do this itself in the software stack?
Another thing I don't understand is: OK, you are required to use GJC-02 for map data in China, and you are not allowed to convert to WGS-84. But then don't. You can directly project the map from GJC-02 to screen pixels, and from WGS-84 to screen pixels, and stuff would line up. And when you tap a point on the screen, you can report the legally mandated GJC-02 coordinates.
- jillesvangurp 2y agoYes, they apply the mandatory conversion and have gotten a license for the software to do this from the Chinese authorities. This wikipedia article has some more details on this: https://en.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China https://en.wikipedia.org/wiki/Restrictions_on_geographic_dat...
- Slartie 2y agoI've been to Shanghai and Beijing in 2010 or so, and I vividly remember that my iPhone 3G (that I jailbroke and unlocked to be able to use local Chinese SIMs, oh, those were the times...) didn't work at all for the purpose of getting around, because Google Maps GPS locations didn't match up with the map. However, there was some obscure third-party mapping software available in the app store (I think it was even the official one, not Cydia) which basically showed a Google Maps view and drew the GPS dot onto it by itself, applying the conversion first and thus fixing the display problem. So at least back then Google Maps apparently didn't yet convert the GPS coordinates to the weird obfuscated Chinese system. But it was a big nuisance and took me a while to figure out. For the first days I thought my jailbreaking activity would have broken the GPS chip or something.