Difference between revisions of "China datums"
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Revision as of 01:36, 1 March 2012
Datums in China
Coordinate systems used in China
Paper maps
Web maps
觀測中國電子地圖諸網站常見座標系統， An observation of Chinese web mapping sites shows various non longitude / latitude systems in use.
Very many of them are plain Mercator projections. They are visible in the URLs generated when "sharing" map views with friends.
One finds one can replicate very closely the results of e.g., Sogou API (type=1) using the following parameters, here as we take a diagonal swath through the country:
$ perl -wle 'for($x=90, $y=20; $y<=50; $x++, $y++){print "$x $y"}'|
proj -E +proj=merc +k_0=1.000010881 +rf=294.9787 +a=6378137
...
116 46 12913201.44 5749320.52
117 47 13024522.14 5910526.61
118 48 13135842.84 6074798.25
119 49 13247163.55 6242305.46
120 50 13358484.25 6413230.50
Indeed, the only differences that remain appear to be the state mandated distortion... 似乎僅留政府所規定之偏移…