doi:10.16186/j.cnki.1673-9787.2021110123

Received:2022/11/28

Revised:2023/02/21

Published:2024/03/25

Boundary smoothing for volume rendering of 3D lithology grid model in engineering geology

ZHOU Ying1，NIU Lujia1，WANG Zhangang1，ZHANG Xi2，XU Zhaoshang3

1.College of Geoscience and Surveying Engineering，China University of Mining & Technology （Beijing），Beijing 100083，China；2.BGI Engineering Consultants Ltd.，Beijing 100038，China；3.Planning and Construction Bureau，Hebei Xiongan New Area Management Committee，Baoding 072750，Hebei，China

Abstract: Objectives In order to solve the sawtooth problem caused by the discontinuous transition of lithologic attribute at the boundary of rock strata in the volume rendering process of 3D lithology grid model in engineering geology， Methods a boundary linear smoothing method of 3D lithology grid model subdivision is proposed.According to the characteristics of horizontal continuity of rock strata and the rationality of spatial superposition relationship in vertical direction，and drawing on the idea of connecting adjacent borehole rock formations to the geological interfaces，the lithologic grid is organized into a form of regular division in horizontal direction and vertical recording of top and bottom elevation values of rock segments.Similar to a regularly distributed virtual hole（called a vertical column pillar）.Based on this kind of organization form，in the process of light projection，four strata formation around the sampling point are used to form attribute calculation units，and define the strata connection rules and 16 subdivision templates.Linear calculation of lithological properties at any point in the model space is realized. Results Through the implementation and verification of WebGL2.0 in GPU，it is concluded that the rock vertical boundary on the longitudinal direction can be significantly smoothed，which solves the sawtooth problem in volume drawing of rock boundaries.Finally，the calculation of the lithologic attribute at the sampling point is realized and the effect after smoothing is obtained. Conclusions The results show that the characteristics of the rock strata are combined with the spatial sampling process of the volume drawing ray projection algorithm，and the smoothing effect is good for the engineering geological rock strata with the assumption of horizontal continuity，and provide a new idea for the visualization of lithology grid in engineering geology.However，because there is no clear sequence relationship between rock strata，the belt fault model cannot be processed，nor can the transverse disconnection of large dip rock strata be dealt with.

Key words:3D lithology grid；ray casting；aliasing problem；volume rendering；smooth