Curve continuity, in a sense, defines the smoothness of intersections between the ends of the foreign curve and other geometry in the model. It also defines the continuity of three-dimensional geometry created from the curve, such as a swept surface. First-order continuity implies that the first derivatives of two adjoining curve segments are equal at the point at which the curves join. Second-order continuity is similarly defined. Depending on the curve continuity you want, the evaluator function needs to contain first and second derivatives of the parameterized curve equations.

You specify the curve continuity using the PRO_E_CURVE_CONTINUITY element in the element tree. The valid values, contained in the enumerated type ProForeignCrvCont, are as follows:

These values correspond to zeroth-, first-, and second-order continuity, respectively. If you use the value PRO_FOREIGN_CURVE_CALC_XYZ, passes NULL for deriv1 and deriv2 to the evaluation function. Similarly, if you use the value PRO_FOREIGN_CURVE_CALC_XYZ_1_DER, passes NULL for deriv2 to the evaluation function. Therefore, you should check for NULL values of deriv1 and deriv2 in your evaluation function before trying to assign derivative values to them.

calls your evaluation function multiple times for a series of values of the curve parameter, ranging from 0 to 1. The function outputs the following information:

These values are then used by to construct the curve.