| The traditional surveying and mapping methods and the storage and representation methods of geospatial data are totally changed now.The traditional measurement method has a large amount of work,which can not fully reflect the spatial characteristics of the object.After decades of development of 3D laser scanning technology,it can complete the measurement task efficiently and accurately.However,most of the 3D laser point cloud processing software is limited to local machine,the data is only limited to local processing,and the massive data is difficult to share and is not conducive to multi-party collaborative work.It is one of the important needs to share data with the outside world timely and effectively in the completion survey and daily operation stages,so that experts from other places can quickly analyze and put forward opinions.The biggest advantage of using web browser to process subway tunnel information is that there is no need for any additional plug-ins and services can be obtained anywhere.Therefore,it has a certain application value to realize the rapid visualization of subway tunnel point cloud data on the web.Because of the feature of the tunnel space structure,most of the indexing algorithms can not be directly applied to the tunnel point cloud data,and the algorithm of quickly building the index for the tunnel point cloud also has certain scientific significance.In the related technical field,the research work of scholars at home and abroad has a high reference value.On the basis of these research results,this paper mainly solves three problems around the display and processing of metro tunnel point cloud in browser.The First One is the huge amount of point cloud data,which takes a long time to process.In order to complete the processing of tunnel data quickly,in this paper,according to the spatial characteristics of metro tunnel,after the research of related index algorithm,the point cloud index combining grid and multi-resolution octree is realized to improve the efficiency of point cloud processing.Second,it is difficult for browsers to render 3D images.In this paper,WebGL is used to optimize the rendering mechanism,enhance the rendering effect,and realize the rendering and display of point cloud on the web.The program could adapt different network speed and hardware configuration.The third is to realize the stable data interaction between the server and the host,and the relevant configuration can adapt to different server environments.FTP file transfer protocol is used to solve the problem of stable transfer of massive point cloud data.Based on QT platform and xampp framework,the application can quickly establish the subway tunnel point cloud index,index data can be uploaded to the server stably,and finally rendered and displayed on the browser.Simple measurement operation can be carried out on the web page,which initially meets the actual engineering application requirements.Finally,this paper used the point cloud data obtained from Wuhan city ‘s subway tunnel to carry out a number of experimental analysis.The experiment is divided into five parts.The first part compares the construction efficiency of hybrid index and octree index in the subway tunnel point cloud.The second part analyzes the influence of the parameters of the improved multi-resolution octree node data structure on the index construction time,and finds the relatively appropriate value.The third part observes the hybrid index and single multi-resolution octree index The fourth part tests the relationship between the maximum rendering number of point cloud and the frame rate under different video cards.The fifth part tests the impact of network speed on the response of Web point cloud rendering,and gets the network speed that can meet the needs of Web point cloud visual interaction at least.Several experimental results and final rendering results show that this method can effectively complete the interactive task of point cloud network browsing in metro tunnel. |
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