Correctness Of Free Form Surface FittingAlgorithms

In this paper we consider the problem of fitting a fixed, free form surface to coordinate data. We describe an algorithm using a separation of variables approach that allows probe radius compensation to be implemented in an accurate and simple way. We also show how to generate test data with which to validate surface,fitting algorithms. By comparison with the surface3itting problem, the data generation is extremely straightforward and requires onlra capability to generate points lying exactly on a surface along with their corresponding normal vectors. The data generation also caters for probe radius compensation in a simple way. The main advantage of the data"generation scheme is that it allows the behaviour of approximate solution algorithms to be assessed without the need to implement a comprehensive algorith~n that addresses the true computational aim. We illustrate this approach on aspheric surfaces.