Rhino BlendSrf Should read edge degree/point instead of fitting to tolerance

I’ve been using VSR for a few years now, and frankly I’d be lost without it. However, now that VSR is an Autodesk property, and with what we’ve seen of how often T-Splines gets updated now…I’m starting to worry that there won’t be a Rhino V6 version of VSR. After using VSR, one thing I really start to notice is how many Rhino commands create surfaces with excess points, for no good reason at all. Here’s a perfect example:

The surfaces being blended are untrimmed mirrors of a very simple degree5/1 single span surface. The VSR blend creates a degree 5/5 single span surface. Rhino’s BlendSrf creates a surface that’s degree 5/6 points in the V direction, but instead of “reading” the opposite edges and realizing they are both degree 5/6 points, it builds a surface that is degree 3 to within file tolerance, which in this case is 28 points!!! So from VSR we have a surface that is easily editable, whereas from Rhino the surface is too dense to do any sculpting with, if it was so desired. Thoughts?


Hi Sky - BlendSrf uses Sweep2 and refits the rails (input edges) not knowing enough, I guess, to use the SimpleSweep part of Sweep2. In cases like your example, I use a loft followed by MatchSrf to keep things light but it would be nice if BlendSrf could recognize the ‘simple sweep’ situation as you point out.

@Lowell, is this possible ( pronounced ‘reasonable’) to add?


You dovetail so nicely into my other complaints @pascal :slight_smile: Sweep should default to “simple” whenever possible. It just feels like Rhino fights the user tooth and nail to get clean simple surfaces, when it should be just the opposite.

Also, if you use Loft and try to match start and end tangents, you get this:

Of course you could Loft a straight section, use ChangeDegree to set the U direction to degree 5, and then run MatchSrf, but that just underscores my point that what should be a super simple operation (and surface) is unnecessarily complex.

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Yeah, I seldom use that feature myself, unless I need the loft to pass through a specific middle curve. Straight loft, then MatchSrf. MatchSrf does the degree changing as needed, on its own, you only need to tell it what contunuity to keep at the other end.


I’d say its possible and reasonable to use simple sweep in blendsrf.

Both sweep1 and sweep2 do use simple sweeps when possible in Rhino6

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Thanks Lowell, that would be great!



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Yes!!! Thank you :smile:


That is so true. I have the exact same feeling now and then…