China datums
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Datums in China
Please see e.g., http://www.asprs.org/a/resources/grids/05-2000-china.pdf . On this page we aim to just supplement the more widely known information.
Coordinate systems used in China
Web map examples
Some common coordinate systems observed, 觀測中國電子地圖諸網站常見座標系統，
Here we give examples of how a single longitude latitude pair is located differently depending on which web mapping site one uses!
This is necessitated by the state mandated distortion... 其政府所規定之偏移…
- http://maps.google.com/maps?q=loc:40,116.5&t=k
- http://ditu.google.com/maps?q=loc:40,116.5&t=k
- http://api.map.baidu.com/staticimage?markers=116.5,40&zoom=14
Also we observe various non longitude / latitude systems in use.
- 搜狗 Sogou API (type=1)
This is a plain Mercator projections. Experimentation proves they are merely using the Clarke 1866 ellipsoid, a=6378206.4 rf=294.978698213898 .
$ proj +proj=merc +ellps=clrk66
Note not all sites are actually reachable from inside China, as one can test,