ExtrudeCrvTapered produces inaccurate tapered extrusions when the starting curves are curved and have few control points. The inaccuracy increases with increasing length of extrusion and curvature. It occurs with extrusions which are not long enough for creases to occur.
Examples are in: TExtProb21.3dm (226.1 KB) These examples have a taper angle of 45 degrees and an extrusion length of 25mm. Example 1 has a start curve with 5 control points, was extruded down with the radius of curvature increasing. Example 2 has a start curve with 4 control points, was extruded up with the radius of curvature decreasing. The minimum radius of curvature of the start curve is 27.4mm and the offset distance was 25 mm so the offset curve does not have a kink.
The correct shapes of the ends of the extrusions opposite the start curves are shown by the moved offset curves. Clearly the extrusions have an incorrect shape. Rebuilding the start curves with a much greater number of control points, 100 rather than 4 and 5, produces much more accurate results. The cause of the problem appears to be that the algorithm does not divide the start curve sufficiently before calculating the shape of the opposite end of the extrusion. It is not clear what is used to determine how finely the start curve is divided for the calculations - the various accuracy settings do not appear to have any effect.
This problem was previously reported in the ExtrudeCrvTapered - bad result thread with a different example. That thread generated considerable discussion. This thread is an attempt to more concisely report the problem with a simpler example along with the apparent cause.