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.
If you are doing modern work, you should only see CGCS2000 (EPSG:4490), which is close to ITRS and WGS 84 for casual use. Parameters for precision transforms is not officially given, but you can try your luck with Wang et al. (2019), Table 1.
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://maps.google.com/maps?q=loc:40,116.5&t=m
- 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.)