1.http://www.embhelp.com/drew/algorithm/shortpath.htm
2.http://web.mit.edu/16.412j/www/html/papers/original_dstar_icra94.pdf
3.http://www.frc.ri.cmu.edu/projects/mars/publications/focussed_dstar_ijcai95.pdf
4.http://numenzq.iteye.com/blog/160396
5.http://www.embhelp.com/drew/algorithm/shortpath.htm