Abstract:

The roaming function is widely used in the fields of digital earth, virtual reality and simulation. Previous researches mostly focused on desktop applications under client/server(C/S) structure. This paper constructs a virtual Earth based on Cesium, an open-source 3D geography framework on the Web side under browser/server(B/S) structure and designs three different roaming algorithms: conventional algorithm, callback function algorithm and Lagrange interpolation algorithm. Then, the tilting photography model of downtown Chongqing was successfully loaded on the virtual Earth’s surface to realize the roaming functions of the three different algorithms. Finally, the effectiveness of the three algorithms was compared in terms of frames per second (FPS) and network latency (NL). The results show that the average FPS in the first 50 s for conventional algorithm, callback function algorithm and Lagrange interpolation algorithm are 70, 74 and 80 Hz, respectively; The average NL in the first 50 s for conventional algorithm, callback function algorithm and Lagrange interpolation algorithm are 14.145, 13.166 and 12.419 ms, respectively. In terms of FPS, callback function algorithm is 5.714% higher than conventional algorithm, while Lagrange interpolation algorithm is 14.286% higher than conventional algorithm. In terms of NL, callback function algorithm is 6.921% shorter than conventional algorithm, while Lagrange interpolation algorithm is 12.202% shorter than conventional algorithm. Overall, the final order of the three algorithms’ running efficiency from largest to smallest is: Lagrange interpolation algorithm, callback function algorithm, and conventional algorithm. Namely, callback function algorithm and Lagrange interpolation algorithm have certain improvements compared with conventional algorithm in the process of roaming, and Lagrange interpolation algorithm can achieve the most efficient and smooth operation and rendering effects.

Key words: Cesium, B/S, roaming algorithms, FPS, NL