球面距离的计算

http://blog.csdn.net/liminlu0314/article/details/8553926

http://blog.csdn.net/u011833609/article/details/18057079

http://geokoder.com/distances

http://www.techques.com/question/1-4463907/How-do-I-know-if-a-Lat,Lng-point-is-contained-within-a-circle

http://www.cnblogs.com/LBSer/p/3298057.html

http://uohzoaix.github.io/studies/2013/05/16/geohashAlgorithm/