ABSTRACT
It is convenient to consider two aspects of the conversion process: exact conversion and approximate conversion. Exact conversion simply means to change representation, for example, increasing the degree, using more polyno mial patches, or just use a different representation. In approximate conversion we would like to compute a piecewise polynomial approximation to a given piecewise polynomial surface. The approximation is normally required to have a certain degree (which could be either higher, equal, or lower), and then the number and location of the patches for the approximation should be adjusted so that the error is within a given tolerance. In degree reduction we would normally have to increase the number of patches, while in degree raising the number of patches can sometimes be reduced.
