Tessellated Modellers:

This explains a class of simplified boundary-representation modellers that approximate to curved faces by a number of plane faces. As these modellers are limited to plane faces and this implies that all of the edges are linear and all of the loops are closed polygons. This restriction considerably decrease the amount of calculation needed to display the output and so speeds things up. This also simplifies the calculation of intersections and the hidden- line or hidden-surface removal.

Though there are penalties connected with this type of modeller. Some of the objects are very hard to represent, a simple instance of such an object is a ball or sphere. For this kind of curved surface, the user has a choice among accepting a very poor approximation or enhancing the number of plane facets to the point where all of the earlier advantages are lost in the sheer volume of data produced.

For applications where mostly objects are composed of flat faces, this kind of modeller is extremely efficient and provides a perfectly sufficient representation of the data. One such instance is architecture where most of the surfaces produced are made up of plane facets. The major lesson to be learnt from this discussion is that modellers must be chosen to fit the required application.

While attempting to economise on storage, this is possible to store objects expressed in terms of their faces alone, the edges can then be calculated from the intersections of the faces if they are needed.

This is less satisfactary to store the object defined by its edges alone. The object illustrated in Figure shows the problems with this approach. It is clear that this example is a cube with a slit in it. Though without additional information, this is impossible to tell whether the slit runs from top to bottom, from front to back or from left to right.