proj4.defs("EPSG:6721","+proj=tmerc +lat_0=0 +lon_0=105.625 +k=1.00002514 +x_0=50000 +y_0=1300000 +ellps=GRS80 +towgs84=61.55,-10.87,-40.19,-39.4924,-32.7221,-32.8979,-9.994 +units=m +no_defs +type=crs");