Funding for this research was provided by:
Open Funding Project of State Key Laboratory of Virtual Reality Technology and Systems of Beihang University (BUAA-VR-15KF-14)
National Natural Science Foundation of China (61532002, 61272199)
National High-tech Research and Development Program of China (2015AA016404)
Specialized Research Fund for Doctoral Program of Higher Education (20130076110008,)