Any diameter in the circle generatrix may be considered as an axis of a sphere.So, on the spherical surface there are three kinds of latitude-circles .

• (圆母线的任一直径均可看作是球的轴线，因此，在球面上有三种纬圆．他们分别是正平纬圆，水平纬圆，侧平纬圆。