Difference between revisions of "China datums"

Revision as of 04:12, 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.

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.

Also a factor is the state mandated distortion... 另需考慮政府所規定之偏移…

Experimentation proves they are merely using the Clarke 1866 ellipsoid, a=6378206.4 rf=294.978698213898 .

$ proj +proj=merc +ellps=clrk66

Here we give examples of how a single longitude latitude pair is located differently depending on which web mapping site one uses!

Note not all sites are actually reachable from inside China, as one can test,

@@ Line 25: / Line 25: @@
 ====Google====
 *WGS84 longitude / latitude
+==Examples==
+Here we give examples of how a single longitude latitude pair is
+located differently depending on which web mapping site one uses!
+*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
+Note not all sites are actually reachable from inside China, as one can test,
+*http://www.greatfirewallofchina.org/index.php?siteurl=ditu.google.cn
 ==See also==