Study On The Technology Of OpenGL_based Reconstruction Of Geometric Model From Step File

With the development of CIMS in the manufacturing, CAX technology has beenwidely applied to industries. More and more users need to exchange product data betweendifferent application systems. The key to solve this problem is to establish a unifiedstandard for the exchange of product model data to support different application systems.STEP was put forward under such circumstance. Its purpose is to provide a neutralmechanism without dependency on a specific system, which can describe the product dataof the entire life cycle; meanwhile keep the consistency and integrity of the data.Firstly, this paper deeply analyzes the STEP neutral file and the application protocol ofAP203. We must understand AP203if we want to extract information of STEP neutral file.The application protocol of AP203describes the expression of three-dimensional entitymodel. This paper analyzes geometric entities and topological entities of the applicationprotocol of AP203in detail, which set the stage for the next information extraction.Then, develop model parser for STEP neutral file. Model parser mainly consists ofthree modules, namely: information management module, information storage module,information extraction module. Information management module defines the pointeraddress and corresponding map collection of the entities in the AP203. Information storagemodule is responsible for adding the data of the whole file to the map collection ofcorresponding keyword, then establish the relationships between entities according torelational model of entity reference of the application protocol of AP203. Informationextraction module is responsible for identifying the model and extracts the correspondinginformation according to the type of face, which lay the foundation for reconstruction ofthree-dimensional entity model.Finally, take advantage of OpenGL function to reconstruct the three-dimensionalentity model on the applications platform without distortion. The specific implementationmethod is to describe various forms by the method of NURBS unifiedly, and then use thesurface display and surface cutting functions of OpenGL to display various surfaces, so asto display the entire model.