参考：
http://cdn.hujiulong.com/geohey/blog/mercator/play.html
https://www.cnblogs.com/rainbow70626/p/7989907.html
https://www.cnblogs.com/DHUtoBUAA/p/6706642.html
墨卡托投影
原文：https://www.cnblogs.com/yibeimingyue/p/10290485.html
