support mercator projection coordinates about gcoord HOT 2 CLOSED

@abc2888630 高德地图使用的是GCJ02而不是EPSG4326，应该这样写

let test = gcoord.transform( lonlat, gcoord.GCJ02, gcoord.BD09 );

另外有问题建议单独开一个issue

from gcoord.

let center = [12959773,4853101];//同样用在高德和百度上
let lonlat = ol.proj.transform(center, "EPSG:3857", "EPSG:4326");
//lonlat116.41962164619503,39.91157563865826，这是在高德上定位在北京***附件

let test = gcoord.transform(lonlat, gcoord.EPSG4326, gcoord.BD09)
//test:116.43231866009562,39.91904444259852，转换后的百度，定位到北京郊区去了

得到结果不大精确
////lonlat116.41962164619503,39.71837291000932这是自己调整后，得到的在百度地图上定位***附件的坐标

from gcoord.