Research On 3D Reconstruction Technology Of Engineering Drawing Based On Secondary Development Of AutoCAD

Engineering drawing has become the standard language to express the concept of machine design.It still plays an important role in today's industrial era.Many computer aided product analysis techniques such as finite element analysis,Interference inspection of mechanism assembly,process design,numerical control machining,simulation display,etc.can not directly use the geometric and topological information in the two-dimensional engineering drawings,therefore,the conversion technology from 2D engineering drawings to 3D entities is particularly important for maintenance and sustainable development of product design.AutoCAD occupies an important position in the field of graphic design and three-dimensional design,such as architecture,civil engineering,machinery,decoration and so on.In particular,it is regarded as standard drawing software in the field of engineering drawing.In this reconstruction system,DXF files are used as data source files to complete automatic transformation of 2D engineering drawings to 3D entities.The reconstruction system is divided into three parts: two dimensional information extraction links,three dimensional reconstruction preprocessing links and three dimensional entity reconstruction links.The main task of the two-dimensional information extraction link is to write an interface program written in C language that extracts the geometric information,topology information,and dimensioning information of the primitive of the two-dimensional engineering drawing.And section area information extraction algorithm of the full-section view,half-section view,partial cross-section view,full cross-section view obtained by several intersecting planes,full-section view obtained by several parallel planes are also proposed.The extracted information is stored in a data link list as an input to a three-dimensional reconstruction preprocessing system,and preprocessing algorithms for half-section,full-section,partial-section,intersection-section and parallel-section are discussed.The view segmentation block in the 3D reconstruction preprocessing section improves the traditional angle discrimination method in terms of the efficiency of the contour search,and uses this method together with the coordinate projection method to complete the view segmentation of the engineering drawing with multiple views.In the section called “Building Data Structures for 3D Reconstruction”,establish a double-linked list structure and summarize the information of graphic elements in the data link list according to the levels of points,lines,and surfaces.The association of the view linked list with the element linked list,the wireframe linked list with the wire linked list,the wire linked list with the point linked list,the wire linked list with the dimension linked list,the basic view associated with the auxiliary view,the cut area linked list and the view linked list through a pointer.The establishment of three-dimensional solid reconstruction system is based on the secondary development technology of AutoCAD platform,using object-oriented programming methods,using the classes and functions provided by ObjectARX,the ObjectARX program is compiled in the VC++6.0 environment,and call ARX program in AutoCAD to generate primitives.According to the relative position relationship of the contour in the view,the relative positional relationship of the primitives in space is inferred.Boolean operations are used to combine the primitives at the correct positions,and finally the assembly that meets the projection relation of the drawing view is generated.Using the reconstruction method proposed in this paper combined with two-dimensional engineering drawings for three-dimensional reconstruction experiments,the results show that the reconstruction of the engineering drawings including full-section view,half-section view,and partial section view has a good reconstruction effect.