Abstract: Since computer simulation systems and virtual reality systems developed by the application of Web3D engine needs to run in a Web browser, downloading and running these systems shall be fast. It requires that the calculation speed of Web3D engine including picking function shall be improved as far as possible. A hierarchical algorithm of rays intersection is presented. The first layer is a rapid object selection by AABB algorithm, the second layer is the improvement to the picking precision by triangle algorithm. Based on the proposed algorithm, the picking function of selecting figure object is implemented on an open source Web3D engine by JAVA language.

Key words: computer application, picking 3D figure, hierarchical ray intersection algorithm, Web3D engine