I wonder if I am not understanding Rhino Tween command, as I am able to get a more functional and understandable result from Adobe Illustrator Blending. See attached file:
- note how illustrator blending rounds the corners of the rectangle as it gets closer to the circular curve.
I think that’s really down to personal taste. Both results are valid IMHO.
When blending from a sharp corner to a round feature, you really need to decide what to preserve. Illustrator favors roundness, while Rhino preserves sharp features as long as possible. Illustrator actually blends CP position while Rhino sweeps a straight line between the curves and then extracts parallel isocurves. Both techniques are valid and functional but give different results.
Another difference is that Illustrator works with Bézier splines, while Rhino works with NURBS. An Illustrator circle is not really a circle, it’s a sort of round thing.
You can approximate the Illustrator behavior in Rhino by using a deformable circle and a rounded rectangle. I changed the degree of the rounded rectangle to 3 and made it deformable, and moved the seam to the logical point. The resulting control point structure is however much more complex in Rhino due to the NURBS.
Thank you both (Halo & Mitch) for your suggestions. I realize that the bezier curve construction is unique and different from the control point curve tool available in Rhino 5, and that this style of drawing tool lends itself to NURBS construction.
However, for me the word “tweening” suggests a metamorphosis from one shape to another (without limitation over a specified number of steps). And I think Illustrator demonstrates the ability to go from hard cornered rectangle to circle, in a very realistic transition.
It would be nice if Rhino could use the bezier tool available from its quiver of drawing tools to complete the Tween command, (much like Illustrator) then auto rebuild that Tween series of curves, to be a NURBS friendly control point structure.
Here is my best solution: By pushing 5 control points to each corner of the rectangle, and maintaining 20 points for each shape and Level 3 NURBS. I get more rounding from the corners of the near rectangle (corners are still slightly rounded).