Surfaces refuse to extend

They do change (very little), but you have to “nudge” them about half a dozen times in order to get them where you want:


(They were all created by extracting iso curves and then doing a fin.)

extend.3dm (54.9 KB)
extendstubborn.3dm (55.4 KB) (this one takes more than a dozen commands to extend inwards…)

After rebuilding the surfaces, they extend without problems

or FitSrf command

Thanks for the workaround, but you realize that I’m extending in the V direction which is degree 1, and that doesn’t really need rebuilding?

Also, as I mentioned, with a little patience (and a lot of clicks), the surfaces do extend even without re-building, so Rhino is clearly capable of it. I’m crossing my fingers for them to fix this (since it does crop up quite a lot of times for me).

I mean, if they fix this… maybe there’s a glimmer of hope for extending open polysurfaces in the future (with chainedge)…

This is the complete thing I’m extending, and right now, it’s quite a number of operations for something that should be really simple:


1 Like

this problem is because the surface is rational
it’s a bug in rhino


Great, so it’s the same bug as this one that I already reported then.

What the heck, that’s why I specifically wrote that the surface was created by the Fin command.

Has Rhino really been unable to extend surfaces created by its own commands for the last 20 years?

Yes exactly
it’s the same problem.
I encounter this kind of problem often
… however I have noticed that this problem often occurs when the objects are too small
I don’t know if this has a relation to tolerance or not

it’s a serious problem !!!

Since it seems a problem in the weight of control point , tolerance - may be a problem not necessarily Rhino mathematics, can be a problem of the computer itself, the mathematical coprocessor.

Can you post a file with just the original isocurve and maybe a second curve for the direction?

Reengineering is a positive result.

So what’s the source of this rational surface?

“Tolerance” problems in Rhino have nothing to do with hardware.

Why don’t you fix these problems then?
And why is there never such a problem with the command Fin on my equipment?

Added these files to this bug RH-60330 ExtendSrf: Inaccurate on rational surface

1 Like