先收集,再补充
向量 http://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect/565282#
参数方程:http://book.2cto.com/201208/2894.html
定比分点:http://blog.csdn.net/dgq8211/article/details/7952825
解直线方程(行列式):http://www.cnblogs.com/i-gps/archive/2012/06/19/2554992.html
//判断点和直线/线段的位置关系
//在直线某一侧