How to Use Coordinate Converter
The Coordinate Converter lets you transform geographic coordinates between three systems used in China and globally. Enter the latitude and longitude, select the source coordinate system (From) and the target system (To), then click Convert.
The result shows the converted coordinates to 6 decimal places. You can also click the ⇄ Swap button to quickly reverse the conversion direction without re-entering values.
Supported conversions:
- WGS84 ↔ GCJ-02
- GCJ-02 ↔ BD-09
- WGS84 ↔ BD-09
Formula & Theory — Coordinate Converter
The Coordinate Converter implements the standard open-source GCJ-02 offset algorithm. The offset is a nonlinear function of latitude and longitude, computed using trigonometric series on the Krasovsky ellipsoid ($a = 6{,}378{,}245$ m, $ee = 0.00669342$).
WGS84 → GCJ-02: Compute latitude offset $\Delta\phi$ and longitude offset $\Delta\lambda$ from the coordinates, then add them to the original values. The reverse (GCJ-02 → WGS84) uses a first-order approximation: $\text{WGS84} \approx 2 \times \text{GCJ-02_input} - \text{GCJ-02}(\text{GCJ-02_input})$.
GCJ-02 → BD-09: Apply a fixed polar coordinate rotation and scale shift ($+0.006° lat$, $+0.0065° lon$ approximately). The reverse undoes this shift.
All conversions return 6 decimal places, giving sub-meter precision for practical use.
Use Cases for Coordinate Converter
The Coordinate Converter is essential for anyone working with Chinese maps and GPS data:
- Map Integration in China — If you collect GPS tracks (WGS84) and need to display them on Amap or Tencent Maps (GCJ-02), the Coordinate Converter corrects the systematic offset so markers align with roads and buildings.
- Baidu Maps Development — Apps that use Baidu Maps API require BD-09 coordinates. Converting from WGS84 or GCJ-02 is necessary to avoid location drift.
- Data Migration — Migrating location data between map providers (e.g., from Baidu to Amap) requires converting between BD-09 and GCJ-02. The Coordinate Converter handles this in one step.
- Mobile App Testing — QA engineers can use the coordinate converter to verify that location pins render correctly across different map SDKs.
- Geographic Research — Researchers analyzing location data from Chinese social media or apps often receive GCJ-02 coordinates that must be converted to WGS84 for global analysis tools.