交集：http://www.boost.org/doc/libs/1_56_0/libs/geometry/doc/html/geometry/reference/algorithms/intersection.html
并集：http://www.boost.org/doc/libs/1_56_0/libs/geometry/doc/html/geometry/reference/algorithms/union_.html
boost geometry下载地址：https://svn.boost.org/svn/boost/trunk/boost/geometry/
