Although NURBS curves and surfaces are analytically generated, to generate and display them requires curves to be approximated by line segments, and surfaces by faces.
Curve approximation controls appear in the creation parameters for curve objects, and in a Curve Approximation rollout for NURBS models (top-level NURBS surface objects). At the model level, the approximation controls affect all curve sub-objects in the model.
Curve approximation is done by segments. A segment of a curve is the portion of the curve between one point or CV point and the next. (For a CV, which doesn’t lie on the curve, the segment is determined by the CV’s parametric knot. The transition from one CV curve segment to another isn’t visible in viewports.) One or more line segments, or steps, are used to approximate each segment of the curve.
Curve approximation parameters aren’t animatable.
Steps: The maximum number of line segments used to approximate each curve segment. If 3DS MAX displays or renders the curve with angles, increase this value. This control is disabled unless you turn off Adaptive. The Steps value can range from 1 to 100.
Optimize: Turn on this check box to optimize the curve. When on, interpolation uses the specified Steps value unless two segments are collinear, in which case they are converted to a single segment.
Adaptive: (The default.) Segments the curve adaptively, based on its curvature. In other words, 3DS MAX assigns the curve more segments points or CVs where its curvature is greatest, fewer points or CVs where its curvature is less.