WebAR-oriented Research On Technology Of Hierarchical Compression Of 3D Models And Dynamic Binding Of Animations

Augmented Reality(AR)is a technology which makes the virtual objects and the real world seamlessly connetced,by superimposing virtual information to the real environment in real time.It has the characteristics of high sense of immersion,complex algorithms and sensitive delay.There are three main implementation forms of AR:dedicated hardware device-based AR,APP-based mobile AR,and broswer-based mobile WebAR.WebAR technology relies on browser technology so that it is lightweight,cross-platform,and low-cost.Different from the former two,the static resources required to construct and render a WebAR page,including the AR algorithm files such as motion tracking and virtual-real fusion rendering,and 3D mesh model files,are all stored on the server side and the work of downloading and transmission only begins when the user requests the page.After the resources are downloaded,the browser needs to execute the AR algorithms and load and render the 3D model.Therefore,WebAR faces the following challenges:the AR algorithms are complicated,resulting in a large amount of real-time calculation;the volume of the 3D model file is large,leading to a large amount of real-time data transmission and high rendering complexity,the transmission delay and rendering delay are high and the delay has an obvious difference in different mobile terminals with heterogeneous network and performance conditions.In response to the above challenges,this paper defines the delay in constructing WebAR pages as the first presentation and displaying time of virtual objects(FPDT).Aiming at reducing FPDT,two optimization mechanisms for the construction and rendering of 3D mesh models of virtual objects are proposed.The specific work is as follows:(1)For the three-dimensional static mesh models,the definition of the vertex merging factor is proposed and its calculation formula is given.Based on the vertex merging factor,a three-dimensional mesh model compression algorithm,and a method of recovering and reconstructing the mesh models are proposed.Based on the above methods and combined with the genetic algorithm,a hierarchical compression and adaptive transmission mechanism of three-dimensional mesh models for WebAR is proposed.The mechanism uses a simplified mesh model which maintains the visual characteristics of the original mesh model as the initial construction and rendering base model,reducing the amount of data transmission and calculation when constructing WebAR pages,and can recover and reconstruct the simplified model level by level on the smart terminals later.(2)For the three-dimensional animation mesh model,the concept of three-dimensional animation separation and dynamic binding are proposed.For the timing of animation binding,a three-dimensional model interactive control mechanism is designed based on the extended ray detection technology.Based on the above concept and interactive control mechanism,an animation separation and dynamic binding mechanism of three-dimensional animation mesh models for WebAR is proposed.In this mechanism,the three-dimensional static model is used as the base model for rendering,and according to the users' interaction event,the animation data file will be downloaded in real time and the animation will be bound to the specified mesh model dynamicly,reducing the amount of animation data which has nothing to do with constrcuting the WebAR page.In order to verify the effectiveness of the above work,this paper conducts functional and performance tests on the above two optimization mechanisms.The test results show that the above two mechanisms can effectively reduce FPDT by 40%to 60%and improve users' AR experience.