Blend Issue


(Joaquin Laborda) #1

Hi All,

I want to create a blend between 2 surfaces, and I’m working with bezier surfaces. The new enhanced blend now respects the structure of the edge if the edges have the same structure, but with the surfaces I’m working now the blend result is not what I expected, even if I extract the edges or create a loft between the edges the result is more complex than expected.
If I rebuild the surfaces with the same degree and points then everything works fine, the form changes… but it works.
So, what I want to know is why should I rebuild the surface to get a surfaces that respect the original structure of the edges. Or what is wrong with this edges or surfaces?

Then I tried rebuilding the edges of the original surfaces and again the result was fine.
So my second question is: if a surface is untrimmed, why is the structure of the edge different to the edge?

Attached is the V6 file, I’ll appreciate any help.


V6 Blend Issue.3dm (219.9 KB)

(Rob McPherson) #2

Joaquín, check your original surfaces, they seem to be ‘trimmed’. So those edges aren’t single span. If you do an ‘untrim’ operation on both surfaces then run the blend again it works as expected.

(Rob McPherson) #3

If you need to trim bezier surfaces and still want clean blends then you’ll have to trim them by an extracted iso-curve only.

(Joaquin Laborda) #4

but, why _SelTrimmedSrf and _What say that they are not trimmed?

(Rob McPherson) #5

What command/process did you use to create the surfaces originally?

(Joaquin Laborda) #6

It seems you found the cause, I used ADSurfaceSplit from VSR, the command in case you don’t know, works like a trim but preserving the original shape and rearranging the points to create an untrimmed surface. This is the first time I have this problem. Apparently in this case that I used a double curvature surface to trim the command rebuilt the edge.

(Rob McPherson) #7

Great, glad you found the cause of it!

This is one of the reasons I think we should have a ‘Bezier Only’ mode in Rhino (wishful thinking…).

(Joaquin Laborda) #8

Yes I agree we should have better tools for surface modeling with Bezier. Fortunately some are improving.
I must confess that some years ago I didn’t know how good was to work with the minimum degree and simple structure of the surfaces, but once I knew it I can’t go back.

(Pascal Golay) #9

Hi Joaquin - Untrim or UntrimBorder sorts out the surface edges and makes them untrimmed - you saw that, right?


(Joaquin Laborda) #10

Hi Pascal, I used Untrim but not UntrimBorder to solve it, thanks.