Curves and surfaces in the AcGe library are parametric. A curve is the result of mapping an interval of the real line into 2D or 3D modeling space using an evaluator function with one argument, such as f(u). Similarly, a surface is a mapping from a 2D domain into 3D modeling space using an evaluator function based on two arguments for example, f(u, v). Each 2D and 3D curve class has a getInterval() function that returns the parametric interval. This function has two forms: the first returns the interval; the second returns the interval as well as the start point and endpoint of the curve.
If the interval is unbounded in either direction, the start points and endpoints do not have meaning.