坐标转换：4326转3857

function WGS84ToMercator(lonlat){
    const coord = {
        lat:0,
        lng:0
    };
    const earthRad = 6378137.0; //地球半径
    coord.lat = lonlat.lng * Math.PI / 180 * earthRad;
    const param = lonlat.lat * Math.PI / 180;
    coord.lng = earthRad / 2 * Math.log((1.0 + Math.sin(param)) / (1.0 - Math.sin(param)));
    return coord;
}