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Boundary Representation

An obvious extension to the wireframe method was to represent the polygons composing an object surface, rather than the edges only. This type of method is known as ``boundary representation'', because it describes the boundaries of the solid (in terms of an enclosing surface). Extensions to polyhedral object representations include the use of surfaces specified from b-spline curves. B-spline boundary representation techniques are used heavily in current computer graphics technology for visual effects involving three dimensional objects, and are also sufficient for some machine tool control applications, where the computer system must know the goal shape of the workpiece surface after cutting.

Boundary representation methods are more powerful than wireframes, because they represent an object in terms of its surfaces, rather than its edges. A wireframe can thus be created from any boundary representation, but not necessarily vice-versa (because of possible ambiguity). The use of surfaces prevents the ``missing edge'' problem, and can also prevent ambiguity. Some checking is still necessary, however, to ensure that a given collection of surfaces describes a valid three dimensional object.

Alan Blackwell