The Research On Information Extraction And Pre-processing Of 3D Reconstruction Based On Engineering Drawing

The main task of generating 3D objects from orthographic views is to construct 3D objects according to the geometric and topological information in engineering drawings, which has became an important research direction in CAD/CAM. As the first step of reconstruction, engineering drawing pre-processing plays an important role in 3D reconstruction. Here, under the background of national 973 sub-project, a series of methods of engineering drawing pre-precossing are presented, based on B-rep oriented approach to 3D reconstruction. The main contributions are summarized as follows:1.On reading information from engineering drawing, DXF file format and storing structure is researched, and interface procedure to read primitive data from DXF under CAD system is also designed and programmed.2.On information extraction and recognition, some rules of dimension mark extraction are summarized by analyzing the dimension restriction semantics, then effective methods of extracting text information from heading-table and filtering drawing's peripheral frame are presented, in addition, this paper also discusses cutaway view's recognition and pre-processing.3 . On views separation and coordinate standardization, a coordinate axis projection-based approach and an image scanning-based approach are proposed for views separation, the former reduces the compare times of 2D primitive in drawings and raises the efficiency simultaneously, the latter can separate free nember views of engineering drawing accurately and it has no correlation with complexity of primitive, then, two sets of 2.5D coordinate systems are introduced as intermediates to relate the 2D original drawing system to the 3D space projection coordinates anfd a formal technique is developed for constructing transformation matrices between coordinates.4.On original data arrangement of views, first, this paper discusses the instance of line overlap and gives the concept of hidden point, next, a method for breaking line is put forward by the means of handling two lines intersection, at the end, data check and correction is described through topological relationship between primitives and dimension set of drawing.To make a summary, from the viewpoint of practicality, the method of engineering drawing pre-processing proposed in this paper over comes traditional...