| Boolean operations and CSG modeling method based on Boolean operation are important parts of building three-dimensional entity.They have high application value in CAD/CAE/CAM modeling,virtual design,model simplification and analysis.Boolean operation is the basis of three-dimensional solid modeling,and it is also the core content of CSG modeling method.Local modeling technology and cutting technology make it easier for designers to communicate with computers.It is an important way to modeling and plays an important role in parts design,production and manufacturing.In this paper,after analyzing the existing Boolean operation algorithm,local modeling algorithm and cut algorithm,we study the establishment of basic element,Boolean operation between basic element and the processing of generators from Boolean operation.The main work is as follows:1)Analyze the geometric information and topological information of basic voxels,and transform the prisms and cylinders in any orientation in space by translation and rotation transformation of the positive and negative entities,increasing the diversity of voxel modeling..2)When the intersection of the rectangular plane and the inner ring plane is performed,the intersection line is faulty.This paper proposes a method to determine the phase based on the inner and outer ring information of the surface and the midpoint of the two intersections.Compared with the previous algorithm,this method can correctly obtain the intersection line and has more universal applicability.Then,the coplanar and collinearities in the generator obtained by the Boolean operation are combined to complete the regularization of the entity.3)In order to improve the function of solid modeling,the local modeling technology based on Euler operation,including chamfering,rounding and shelling,has the advantages of simple operation and high calculation efficiency.Among them,chamfering and rounding propose a method of modeling the entity modification using the construction plane.First,the construction plane is formed by the pick-up edge and the size of chamfer or smoothing.Then the intersection of the construction plane and the relevant surface of pick-up edge are obtained,and the information of the relevant surface of pick-up edge is modified.For chamfer,the chamfer surface is formed by connecting the intersection line;for smoothing,by determining the position of pick-up edge relative to the entity,the change of coordinates of points on the arc is determined,and then the smoothing surface is formed.Shell operation is completed by surface-line-point-line-surface process.First,the face of entity is translated the distance of shell thickness in the internal direction of the entity except pick-up surface,and the translation surface is obtained.Then the translation surface is intersected with pick-up surface or translation surface to obtain the intersection line.Then the intersection point is obtained from the intersection line.Finally,the intersection points are connected into lines,and then form the adding surface or the inner ring of pick-up face.4)According to the cutting theory,firstly the cutting plane and the selected reference points are determined,then the section is obtained by intersecting the cutting plane and the entity,finally judge the point of the entity and the selected reference points on the same side of cutting plane to reconstruct the geometric information and obtain the required cutting body.The algorithms designed in this paper are all carried out in the development environment of VC++ 6.0.A large number of test examples are given to verify the stability and completeness of the algorithms. |
