Q. Explain about wire-frame model?

A wire-frame model of an object is the simplest, but more verbose, geometric model that can be used to represent it mathematically in the computer. It is sometimes referred to as a stick figure or an edge representation of the object. The word "wire-frame" is related to the fact that one may image a wire that is bent to follow the object edges to generate the model. Typically, a wire-frame model consists entirely of points, lines, arcs and circles, conics, and curves. For example, a user may, with three dimensional (3-D) wire-frame models, enter 3-D vertices, say (x, y, z), and then join the vertices to form a 3-D object. An example of 3-D object. Wire-frame modeling is the most commonly used technique and is available in all commercial CAD/CAM systems. Wire-frame modeling is considered a natural extension of traditional methods of drafting. Consequently, it does not require extensive training of users; nor does it demand the use of unusual terminology as surfaces and solids.

Early wire-frame modeling techniques, developed in the 1960s, were strictly two dimensional and were designed to automate drafting and simple NC program verification. In those days, users had to construct the geometry of an object in the desired views independently due to the lack of centralized database systems. Later, in the early 1970s, the centralized database concept enabled modeling of three-dimensional objects as wire-frame models that can be subject to three-dimensional transformations. Creating geometry in one view is automatically projected and displayed in other views. This enhances user utilization by saving time and flexibility over manual design and drafting. The major advantage of wire-frame modeling is its simplicity in construction of a model. Therefore, it does not require as much computer time and memory as does surface or solid modeling. However, the user time needed to prepare and/or input data is substantial and increases rapidly with the complexity of the object being modeled. Wire-frame models form the basis for surface models. Most existing surface algorithms require wire-frame entities to generate surfaces. Lastly, the CPU time required to retrieve, edit, or update a wire-frame model is usually small compared to surface or solid models.