Trapezoidal Grid Based Vector Map Dynamic LOD Rendering Method Research

The advent of the era of big data has prompted the growth of human social data types and storage scales at an unprecedented rate.The scale effect of data has brought great challenges to map visualization.The transformation of traditional map visualization methods is happening.With the concept of digital earth,virtual geographic environment,virtual geographic scene proposed,the visualization gradually evolved from the abstract expression of 2D graphics to the 3D realistic display.On solving the problem of large-scale spatial data visualization and real-time rendering,the Level of Detail method is a new model representation method to effectively control the data simplification of complex scenes.However,there is an irreconcilable contradiction between the rendering speed and the storage occupancy of the existing static LOD method.The existing dynamic LOD method is simplified on the original data structure,and then processed to render the graphics elements supported by the graphics hardware.Massive real-time tessellating and memory 10 lead to low rendering efficiency,and it is difficult to meet the rendering requirements of large-scale scenes.Aiming at the shortcomings of the dynamic LOD rendering method under the current perspective projection,this paper uses the similarity of the features of the map features at the adjacent scales and the principle of viewpoint-related,using a data structure that can be simplified and directly used for rendering and designs its simplified algorithm,unites the process of simplification and tessellation.Based on this,the dynamic LOD rendering method in hardware environment is further studied.This method avoids the problem of computational redundancy and data redundancy in the traditional method,improves the rendering efficiency of the map and provides a new solution for rendering the vector features in the 3D scene.(1)Simplified algorithm design for the trapezoidal grid under perspective projection.First of all,this paper designs a viewpoint-related weight calculation method.After that,using the tessellating result of the line and polygon features are completed for the construction of the trapezoidal grid.Finally,based on the trapezoidal grid structure,taking into account the principle of topology preservation and consistency,the simplified rules are designed to simplify the algorithm of the perspective projection line and polygon trapezoidal grid and propose a method to avoid the self-intersection of the trapezoidal grid.Unite the simplification and the tessellating in the LOD rendering process.(2)Trapezoidal grid based vector map dynamic LOD rendering method.Firstly,explore the influencing factors of map simplification,and analyze the impact of map visibility and feature visibility on map simplification in detail.Secondly,according to the trapezoidal grid and its simplified algorithm,the progressive rule of the efficient trapezoidal grid is designed to simplify the trapezoidal grid efficiently,and the element buffer object data update method before and after the trapezoidal grid simplification is studied.Finally,a dynamic LOD rendering method for viewpoint-related vector maps in hardware environment is designed,which is simply symbolized and designed with map cache to speed up its rendering.(3)Map visual platform design.Based on the above research results,the rendering engine framework of the visual platform is designed and the algorithm proposed in this paper is implemented.The feasibility of this method is verified by the rendering effect experiment By comparing the progressive method with the Mapbox vector tile method,the practicability and efficiency of the proposed method in practical application are verified,and the rendering efficiency is improved.The method of this paper provides a new solution for vector map rendering and big data exploratory analysis in 3D scenes.