The best method for the three-dimensional model constructions is the solid modeling technique. It provides the user with complete information about the method. When color is added to the solid model, the resulting picture becomes very realistic. All solid modeling systems provide facilities for creating, modifying and inspecting models of three dimensional solid objects. The following representation schemes are available for creating solid models. 1. Constructive solid geometry (CSG) (or) C-rep 2. Boundary representation (B-rep) 3. Pure primitive instancing 5. Cellular decomposition
1. Constructive solid geometry
· It is also called a building block approach. · A Combination of simpler solid objects makes the CSG model. · Boolean operators are used for combining the primitives form the complete solid object. · Simplest solid objects are termed as primitives. Some of the primitives are cubes, spheres, cylinders, cones, rectangular blocks, etc. · The available Boolean operators are union (U or +), Intersection (n) and the difference (-)
CSG Using Boolean Operators
When two or more solids are combined with the Boolean operator union, the result is the single solid incorporating all the space occupied by any of the individual components. Simply, this is like adding components together. When two (or) more solids are combined with the Boolean operator difference, the result is the single solid incorporating the space, which is occupied by the first component but is outside all of the remaining components. This is like subtracting the second and subsequent components from the first components. When two or more solids combined with the intersection, the result is a single object incorporating the by space, which is occupied in common by each of the components
2. Boundary representation (B-rep) method
In the boundary representation scheme, a solid is represented by the data containing the elements, which describes its boundary. These elements are divided into topological elements and geometric elements. The topological elements, which are vertex, edge, and face. The geometric elements are point, curve, and surface.
These geometric elements are linked to the appropriated to topological elements are follows:
These are two types provided to create a 3D model by the B-rep method. · Topological elements (Vertex, Edge and Face) · Geometrical elements ( Point, Curve, and Surface) · The following is the example for B-rep. the various faces ad formed by vertices and edges. The faces are linked to create the 3D solid model.
It is the combination of both constructive solid geometry and boundary representation approach. It uses the advantages of both approaches. This system is used to increase productivity and to avoid complications in work.
Applications of solid modeling
Solid modeling can be used for the following applications. 1. Creating hidden line drawings, sections, and shaded images. 2. Calculating mass properties such as mass, volume, Centre of gravity, moments of Inertia, Radius of gyration, etc. 3. Self-adaptive finite element mesh generation 4. Kinematics analysis of solid assemblies 5. Process planning for manufacture 6. CNC program generation 7. CNC Tool path simulation and program verification
Advantages of solid modeling
1. Solid models can be created easily. 2. The solid model is complete and more understandable. 3. It provides information about interior details. 4. It is suitable for mass property calculation. 5. It stores more information about geometry.6. Simulation is easy.
Disadvantages of solid modeling
1. The solid model occupies more memory space. 2. It requires more manipulation time.