Researchon System For Web-Based Collaborative 3D Scene Modeling

With the rapid development of Internet technologies, such as HTML5 and WebGL, a large number of Web-based 3D applications have emerged. Unlike traditional Web applications, Web3D applications are facing a serious problem caused by 3D assets. Since 3D assets is larger than text and image files, data transmission will bring inevitable system delays. In addition, due to the characteristics of Web applications, all of the 3D resources must be stored on the server side, so the 3D digital content resources management is a must, and the revision control is one of the most important parts of it. But the prevailing methods are mainly focused on text file rather than binary file. Any changes may cause a whole binary file to be reserved as a new version, which would consume significant storage.This article is mainly researching on the web-based collaborative 3D scene modeling system. In order to solve the problems of serious system latency caused by the transmission of 3D assets, the abstract scene based on scene graph is proposed. Most of the time we only need to transmit the abstract scene in the network, thus greatly reducing the amount of data transmission. In addition, during the synchronous (real-time) collaborative 3D scene modeling, we need to maintain the consistency of shared scene between multiple users. More frequently the user operate, more frequently the data is transmitted. In order to avoid transmission of the entire abstract scene every time, several kinds of abstract operations are introduced to describe a variety of real-time scene modeling operation. In order to improve the efficiency of 3d digital content management, we propose a 3D scene-oriented version control system. By storing and representing the 3D assets as a scene graph, and based on the scene graph structure to design revision control algorithms, we can calculate the difference between different scene versions more efficiently, thereby reducing the storage consumption of version control system. In addition, the non-linear working mode introduced by the version control system has provided a strong support for asynchronous collaborative 3D scene modeling.The main research work is as follows:(1) A nonlinear version control system for 3D scene is designed, and the core idea is to store and represent a variety of 3D scene assets as scene graph. Based on the scene graph data structure, a variety of version control related algorithms, including commit, checkout, branch and tag, diff and merge, are designed. Diff and merge is the most challenging part, we have defined five kinds of state difference and seven kinds of structural difference, and then, based on these differences, we designed a automatic differencing and semi-automatic differential merging algorithm.(2) A web-based collaborative 3D scene modeling framework is proposed, the 3D digit content management is based on the revision control system, and both synchronous and asynchronous collaborative 3D scene modeling are supported. In order to solve the system latency caused by frequent 3D assets transmission, scene assets are split from the scene graph, definitions of abstract scenes and abstract operations are provided.(3) Based on the revision control system for 3D scene, synchronous and asynchronous 3D scene modeling is designed. Operation serialization is adopted by Synchronous collaboration to maintain the consistency of shared scene so as to avoid conflict synergy. Asynchronous collaboration is directly dependent on the nonlinear working model provided by the version control system, and have adopted the optimistic way to discover and resolve conflicts caused by scene sharing.Based on these studies, we design and implement a Web-based collaborative 3D scene modeling prototype system, which is mainly based on open-sourced three.js editor. Three.js editor provides a wealth of scene modeling capabilities, and a variety of common 3D file formats can be converted to the JOS-formatted scene graph, proposed by three.js. Finally, a variety of actual use cases are used to verify the revision control system, synchronous and asynchronous collaborative 3D scene modeling of our prototype system.