Coons Surfaces:

Already we have encountered design tools that originated in car companies; Bezier curves and surfaces were produced by Citroen and Renault in Paris. Two other main concepts also emerged from the automotive field: Coons patches (Coons consulted for Detroit, Ford) and Gordon surfaces (W. Gordon worked for General Motors, Detroit). These methods contain a different flavor than Bezier or B-spline methods: rather than of being explained by control nets, they "fill in" curve networks in order to produced surfaces.

Let us review the part of the design procedure that appreciates this method of modeling. Even in the early days of CAD/CAM, the primary step in the design of a new car is the manual production of a clay or wooden model of that car. The CAD procedure begins with the task of communicating the form of this model to the CAD database.

This communication procedure starts with data acquisition; in this case, the model is digitized : a digitizing device records points (in a fixed coordinate system) where a sensor touches the model surface. This sensor is moved over the model along definite predefined lines, called as feature lines. Thus each line is broken down into a sequence of digitized points. Once these are stored, curves are fitted through them, for instance, by using interpolating splines. Now the resulting network of curves should be completed to generate a full surface description of the model. This procedure - generating a surface from a network of curves - is solved by using Coons and Gordon surfaces.