Bad bug in BlendSrf

Check out blendSrf these two surfaces. the result looks like Donald Ducks beak:

POSITION gives a good result, but tangency and all the curvature continuities messes up.

And if I blend (curve) the edges and run Sweep2 with the result then I get good Tangency result, (And this might have a good reason: but curvature can only be selected for one of the edges, not both at the same time.)

BlendSrf bug.3dm (153.8 KB)

If I later choose to match surface then i can add curvature to both edges.

I now see the problem.

If you detach trim and then trim the surface again BlendSrf works as expected. That suggests there might be something wrtong with the trim boundary.

Sweep2 needs profile curves with 6 control points to curvature match both sides. You can use the rebuild option for that.

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If I remember correctly I trimmed a deformable revolve with a straight line, then shrunk it and then point edited it (then made a copy and 1D scaled it) ((Typical quick hack for sketching))
Why Match surf can handle the edge and blendsrf can’t is maybe the oddest thing.

Hi Jorgen - I do not see this in the current builds here - can you please try the next beta and see if it behaves any better with these surfaces?


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sure thang!

Can you try this file too?

Check if you can match surface them, when I do then I get no warning that Rhino doesn’t manage to do what I ask (in example if I use curvature as match, then I expect Rhino to warn me if it doesn’t manage to do it)
MatchSrf needs warning.3dm (279.9 KB)

Hi Jorgen Hm - yeah, I see that ‘plain’ the result is not so great but that is asking quite a bit - I mean the tool is really not designed for reshaping quite this radically - I’m sure @lowell will have better info about how the thing works, but starting with what you have here just does not seem like a good way to use MatchSrf - you’d want to be a least in the ballpark to start with.


That’s the fun part of teaching… nobody never listen to what they shouldn’t do… But that’s far from the point here, the point is that it should know if it manages to actually deliver what the user asks, because if it fails here and doesn’t tell, then we can not trust it in any other situations either, now can we?