赤道精度与小数位的关系
decimal degrees distanceplaces------------------------------- 0 1.0 111 km1 0.1 11.1 km2 0.01 1.11 km3 0.001 111 m4 0.0001 11.1 m5 0.00001 1.11 m6 0.000001 0.111 m7 0.0000001 1.11 cm8 0.00000001 1.11 mm
参考：https :
//en.wikipedia.org/wiki/Decimal_degrees#Precision
