China datums

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.

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…


 * 1) http://maps.google.com/maps?q=loc:40,116.5&t=k
 * 2) http://maps.google.com/maps?q=loc:40,116.5&t=m
 * 3) *http://ditu.google.com/maps?q=loc:40,116.5&t=k
 * 4) *http://ditu.google.com/maps?q=loc:40,116.5&t=m
 * 5) http://api.map.baidu.com/staticimage?markers=116.5,40&zoom=14

We observe we can obtain the exact same three points,


 * http://map.sogou.com/#hb=1,1&c=12968861,4838218,15&tip=1,12968861,4838218
 * http://map.sogou.com/#hb=1,1&c=12968189,4838039,15&tip=2,12968189,4838039
 * http://map.sogou.com/#hb=1,1&c=12967462,4837158,15&tip=3,12967462,4837158

via 搜狗 Sogou API's type=1, 2, 3. We also notice type=1 is a plain Mercator projection, 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,
 * http://www.greatfirewallofchina.org/index.php?siteurl=ditu.google.cn )