墨卡托航法与中分纬度航法的关系

Discuss the relationship between Mercator sailing and middle latitude sailing

介绍了两种常用的求经差的方法，即墨卡托航法和中分纬度航法．并通过理论推导证明，若将地球形状看作第二近似体，则两种求经差的方法实际上是一致的．

In the theory and practice of navigation, we often meet with the calculation of difference of latitude and difference of longitude. This paper approves that Mercator sailing actually conforms to middle latitude sailing if we take the shape of the earth as spheroid when calculating difference of longitude.