The success in the representation of a solid model lies in the achievement of un-ambiguity in representation. This could be achieved by concentrating in the method of model representation, which gives greater efficiency in visualization. Greater care and proper choice of modeling representation and techniques is very vital in solid modeling. This is because solid modeling the most complicated of the CAD technologies as it represents and simulates an object internally and externally.Methods Used for Model Representation : There are three methods, which are popularly used for model representation. They are CSG, which is otherwise called as features tree, boundary representation and cell enumeration. By making use of these method representations in a proper way, a good solid representation which is accurate, concise, affined invariant, easy acquisition, guaranteed validity, efficient diagram and Boolean operations can be achieved.
CSG or features tree : CSG is otherwise called as constructive-solid-geometry which is a very elegant and efficient combination for representing solid objects. In the CSG or features tree has nodes to denote solids and junctions depicting operations. The starting node is used for depicting the initial stage and the final node depicts the model finally to be outputted. The model has various benefits embedded in it.
Some to name are the path between shows the way in which the final output is to be derived, modification of parameters is easier in this model there by easier to get updated output. However it has to be noted that CSG or features tree is not an independent model, which can be used as such independently. The CSG or features tree has to be derived as boundary representation for achieving the above benefits.
Boundary Representation : This as the name depicts, represents faces of a model by using the bounding edges to depict each face and bounding vertices to define each edge. That is from the initial face one can traverse through any other intermediate faces in the model. The model is otherwise called as facetted model and has many geometric information data of model stored in it.
Some of the geometric information that would get stored normally in this representation is coefficients of the plane in each face, coordinates of each vertex, sine and cosine values and so on. This representation could also be named as surfacing because in this representation solid object is represented by boundary surfaces and then filled to make solid.
Cell Enumeration : In this representation the whole sold is broken down into cubic cells or voxels and the location of each cell is stored. By using this model it is not possible to depict surfaces, which are inclined or curved. If one increases the number of voxels used in this model it gives the benefit of getting more accuracy but with an associated drawback of more storage space requirement. A more upgraded approach of this model, which removed this storage space drawback, was called as octree enumeration representation.
In this model also the solid is broken down into number of smaller pieces but taking into account the other factors like shape, accuracy, storage and this representation proved itself much efficient in terms of storage space.