Technology Research, Based On The Cad-vr Multi-level Detail Model Generation

Interactiving is very important in VR system , but the cost of VR realtime scene rendering is expensive. Smoothness simulation needs 24fps at least. We have to split the difference between geometry veracity of the virtual model and rendering speed of the VR system .A good choice is to use the level-of-detail(LOD)models in VR system now.A mainly way to get VR models is converting and simplifing CAD models now. Though most CAD software corporations have provided VR model translator based on any neutral file formats, there're great shortage in it, users have to do some postprocessing and any functions can't be came true even. Faceting a CAD model and then simplifing the facet model can't get a high quality mesh model because of the vertexs of simplified mesh model isn't on the source CAD surface.This paper expounding the geometry modeling theory and methods of CAD and VR system first, then "The technology of VR level of details models constructing based on UG CAD" is brought forward ,this technology divided the process of LOD VR model constructing into three stages.In the stage of CAD model simplification , the technology of UG CAD model auto-simplification based on feature restraining was put forward .As UG use the feature-modeling method to create CAD model ,we have designed several model simplification rules ,then write codes to carry out the rules and forming the rules code library .Using this library, the detail-feature of UG CAD model can be restraining automatically.In the stage of product data exchanging, a reformative UG NX VRML data exchanging interface was released. ,this module remedy several deficiency of he VRML interface of UG, including the geometry tolerance controling in the course of facet model conversion ,the consistency of assembly hiberarchy and the striping disposal on the triangle mesh.In the stage of polygon mesh simplification, a local triangle mesh model simplification algorithm based on edge collapse was released .This algorithm was particular designed considering the triangle mesh model which output by foregoing VRML translator characteristic.The technology and the method mentioned in this paper was tested and proved in actual projects ,it can reduce the workload of modeling and improve the work efficiency greatly.