利用VB实现墨卡托投影和大圆航线经纬网的简单绘制。实现功能较简单，为课程作业时所写，需要的可以在其基础上进行完善。-Using VB to Realize the Mecato Projection and the Simple Drawing of the Large Diameter Line. The realization of the function is relatively simple, for the course to write, you need to be based on the perfect.