Tessellated Modellers  

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

However there are penalties associated with this type of modeller. Some  objects are very difficult to represent, a simple example of such an object is  a ball or sphere. For this type of curved surface, the user has a choice  between accepting a very poor approximation or increasing the number of  plane facets to the point where all the earlier advantages are lost in the sheer  volume of data generated.