GCJ-02, also known as the Mars coordinate system, is a geographic information system coordinate system formulated by the National Bureau of Surveying and Mapping of China (G means Guojia country, C means Cehui surveying and mapping, and J means Juju) .
The specific method is as follows
function gcj02towgs84 (lng, lat) {
lat = +lat
lng = +lng
if (out_of_china(lng, lat)) {
return [lng, lat]
} else {
let dlat = transformlat(lng - 105.0, lat - 35.0)
let dlng = transformlng(lng - 105.0, lat - 35.0)
let radlat = lat / 180.0 * PI
let magic = Math.sin(radlat)
magic = 1 - ee * magic * magic
let sqrtmagic = Math.sqrt(magic)
dlat = (dlat * 180.0) / ((a * (1 - ee)) / (magic * sqrtmagic) * PI)
dlng = (dlng * 180.0) / (a / sqrtmagic * Math.cos(radlat) * PI)
let mglat = lat + dlat
let mglng = lng + dlng
return [lng * 2 - mglng, lat * 2 - mglat]
}
}