Читать книгу Computer Aided Design and Manufacturing - Zhuming Bi - Страница 62

A wireframe model represents the boundary edges of an object; these edges can be of lines, arcs, and curves. A wireframe model does not include the upper‐level information such as boundary surfaces or volumes. In addition, the results from wireframe modelling have the following limitations:

 All of the edges are displayed as elements in an image and the visibility caused by overlapping is not identifiable.

 No high‐level information related to solids and masses such as surface areas or masses is available.

 The primary data from wireframe modelling is the coordinates of vertices; therefore, the preparation, importing, and processing of modelling data are very time‐consuming and error‐prone.

 The wireframe modelling method is incapable of designing shapes and specifying more complex forms due to the need for a large number of data points.

In addition, due to incompleteness of solid information, a wireframe model may cause the ambiguity of a represented geometry. Figure 2.23 shows two examples whose wireframe models in the left column are not able to distinguish the actual geometrics of objects since their corresponding wireframe models are the same.

Figure 2.23 Ambiguity examples of wireframe models. (a) Wireframe model. (b) Possible solid geometries.

On the other hand, a wireframe model is very concise and fundamental. It can be used as the supporting technique for other modelling methods.