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Objective The impact and fracture of rockfall are important reasons for the difficulty in predicting movement trajectories, and the geometric characteristics of slope bodies are key factors affecting the movement. Methods To study the crushing process of rockfalls and the influence of slope geometry characteristics on the movement of rockfall blocks, discrete element method (PFC2D) simulation technology was used to establish a rockfall free-fall-impact model to analysethe rock mass structure and slope geometry characteristics of typical rockfall disaster points. The fragmentation process of rockfall under different fall heights and impact angles is analysed, and the block motion velocity, crack number and impact force are obtained. Moreover, the two-parameter Weibull distribution is used to describe the fragmentation degree of blocks. Results The experimental results reveal that the fracture process can be divided into three stages: Contact-disintegration, extrusion-fragmentation and independent movement. Rock mass fragmentation starts at the impact point, disintegration occurs along the structural plane first, and fragmentation occurs on the new fracture plane. Sudden changes of the block velocity, crack quantity and impact force occur in the contact-disintegration and compression-fragmentation stages. The block velocity plummets, exhibiting a "step effect", and the impact force rises sharply, revealing a "double peak phenomenon". Moreover, when the fall height increases or the impact angle decreases, the "step effect" and "double peak phenomenon" become more obvious. Under the same impact angle, an increase of the fall height results in the increase of impact kinetic energy, thus increasing the degree of fragmentation and decreasing the particle size distribution range and characteristic particle size. At the same fall height, an increase in the impact angle causes that the contact area is reduced, and the degree of breakage is reduced, increasing the particle size distribution range and characteristic particle size. Conclusion The present results provide technical support for revealing the impact fragmentation mechanism of rockfall slopes and predicting the trajectory of block motion.

The rise of the 6G wireless communication provides a broader prospect for the development of virtual reality panoramic video.The tile-based panoramic video coding scheme can improve the viewing experience of 360° video under the same condition of network bandwidth.Tile partition affects the video transmission performance.Compared with small tiles,using large tiles can effectively improve coding efficiency,but it will cause more pixel overhead by transmitting a larger area to cover the viewport.The existing tile partition work is mainly designed for the rectangular viewport,but the projection of spherical video to a two-dimensional plane will stretch different areas of the viewport to varying degrees in practice.Deriving the pixel overhead associated with covering irregular viewport areas with rectangular tiles is more complicated.To address this challenge,a tile partitioning algorithm for the user's real viewport has been proposed in this paper.Firstly,the stretching distortion of the viewport caused by the projection format is analyzed,and the pixel overhead of the irregular viewport with different tile partition sizes is derived.Secondly,by trading off the pixel overhead and the coding efficiency of tiles with different granularity,an optimal tile partition scheme has been proposed for the panoramic video sequence.Finally,the proposed scheme is compared with the exhaustive search method for tile partition in the experiment,and the results show that the proposed algorithm can achieve almost the same transmission efficiency as the exhaustive search method with less computational complexity.