B-spline control polygon and interpolated contour lines AutoLisp source

It creates the control polygon and interpolates a POLYLINE with cubic B-Spline. The interpolated curve passes through the initial points and you can control its curvature.
The initial polyline can be closed, the function ensuring the continuity of the tangent between the first and the last point.
Can be used in AutoCAD or programs based on IntelliCAD (such as BricsCAD, ProgeCAD, ActCAD, ZWCAD, etc.).
You also have 2 test functions. With the first you can repeatedly select and interpolate POLYLINE entities, and with the 2nd you can generate interpolated contour lines. The 2nd only works if you also bought "Intersect 2 3DFACE AutoLisp source".
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