China Map Coordinate Transform

This tool converts a single latitude / longitude pair between the three coordinate reference systems used across Chinese mapping services: WGS-84 (GPS / international standard), GCJ-02 (Chinese Mars coordinates used by Amap and most domestic apps), and BD-09 (Baidu's offset coordinates). Any source system can be converted to any target system in a single step, with the result shown to 8 decimal places.

1. Enter Input Latitude (-90 to 90, e.g. 39.9042). 2. Enter Input Longitude (-180 to 180, e.g. 116.4074). 3. Pick the From system (WGS-84, GCJ-02, or BD-09). 4. Pick the To system (WGS-84, GCJ-02, or BD-09). 5. Press Convert (or press Enter in an input) to read the result coordinate, with a Copy button for the comma-separated lat,lon string.

WGS-84 is the standard GPS datum used worldwide. GCJ-02 applies China's encrypted offset (computed from a transform of the longitude and latitude plus a geodetic offset using the Krasovsky 1940 ellipsoid constants 6378245 and 0.00669342). BD-09 adds a further Baidu-specific polar offset on top of GCJ-02 using a constant of 300 and a small 0.00006 / 0.00002 perturbation. Cross-system conversions that skip a step (e.g. WGS-84 to BD-09 or BD-09 to WGS-84) are computed by chaining through GCJ-02 internally.