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/
