Supported by the National Natural Scielice Foundation of China under Grant Nos.60573153;60533080(国家自然科学基金);the National High-Tech Research and Development Plan of China under Grant No.2006AA01Z314(国家高技术研究发展计划(863));the Program for New Century Excellent Talents in University of China under Grant No.NCET-05-0519(新世纪优秀人才支持计划);the Natural science Foundation of Zhejiang Provilice of China under Grant No.R105431(浙江省自然科学基金);the Open Project Program of the State Key Laboratory of CAD&CG;Zhejiang University;China under Grant No.A0805(浙江大学CAD&CG国家重点实验宣开放课题)