An integer incremental AOI algorithm for progressive downloading of large scale VRML environments*

Abstract

Progressive data transmission is critical for implementing interactive walkthrough of large scale distributed virtual environments on Internet. This paper proposes an incremental AOI (Area of Interests) algorithm to determine dynamically which VRML objects should be downloaded while the viewpoint is moving in a VRML environment at each step. Our method has three major steps: (1) to divide the entire VRML ground uniformly into a rectangular mesh (m*n grids) along x-axis and y-axis respectively and store all the VRML objects overlapped by each grid into an adjacent list; (2) statically to determine all the grids overlapped by an AOI according to spatial coherence; (3) dynamically to determine newly visible and invisible grids overlapped by a moving AOI at each step, according to the temporal coherence between two consecutive AOI circles; (4) at each step, only newly overlapped VRML objects should be downloaded and rendered incrementally. Thus, the required VRML data downloads can be decreased dramatically at each moving step. Further, the proposed AOI algorithm is an integer incremental algorithm without multiplication, divisions and floating operations, and also it is suitable for hardware implementation. © Springer-Verlag Berlin Heidelberg 2007.