Difference between revisions of "China datums"

Revision as of 20:42, 5 March 2012

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.

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…

We observe we can obtain the exact same three points,

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,

@@ Line 18: / Line 18: @@
 *http://api.map.baidu.com/staticimage?markers=116.5,40&zoom=14
-Also we observe various non longitude /  latitude systems in use.
+We observe we can obtain the exact same three points,
-*[http://map.sogou.com/api/documentation/javascript/api2.0/interface_translate.html 搜狗 Sogou API] (type=1)
+*http://map.sogou.com/#hb=1,1&c=12968861,4838218,15&tip=1,12968861,4838218
-This is a plain [http://en.wikipedia.org/wiki/Mercator_projection Mercator projection]s.
+*http://map.sogou.com/#hb=1,1&c=12968189,4838039,15&tip=2,12968189,4838039
-Experimentation proves they are merely using the
+*http://map.sogou.com/#hb=1,1&c=12967462,4837158,15&tip=3,12967462,4837158
+via [http://map.sogou.com/api/documentation/javascript/api2.0/interface_translate.html 搜狗 Sogou API]'s type=1, 2, 3.
+We also notice type=1 is a plain [http://en.wikipedia.org/wiki/Mercator_projection Mercator projection],
 [http://en.wikipedia.org/wiki/Alexander_Ross_Clarke Clarke] 1866 ellipsoid,
 a=6378206.4 rf=294.978698213898 .