Curve offset fails from just a small change

Why would it have trouble after such a small change in the input surface? (19.2 KB)

The offsetter has no surface to offset on, the surface ends at the border curves and does not cover the offset distance. Even with the surface that you say works, the result is not good, goes to very large values.

I’m sorry, I don’t understand what you mean. If you swap the used surface input node with the unused one, the offset works seemingly good. I can even do this:

I don’t see what you see, so let’s start at the beginning: what version of Rhino are you using, and which service release?

V7 SR37. We do have V8 SR7 but we don’t use it because of bugs and UI issues, and I guess this is another example which confirms how bad of a release V8 is because it doesn’t produce anything:

(Note how I duplicated the graph for the unused node in the example just to see it working and not working side by side…)

The input surface trims have quite high edge tolerances, and may benefit from a re-trim.
The offset distance should be negative to offset into the surface. The curve offset component will then give a result for both surfaces, but one goes way outside the surface still (both on v7 and v8), so a region trim works around that shortcoming.

I would like to encourage you to look at the latest v8 service releases now and then to see if you find that the bugs and UI issues you saw earlier are resolved. If not, point us in the right direction with our efforts to solve them by making topics here on Discourse.

The shortcoming I mentioned above has been reported in a YouTrack item. (15.9 KB)

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One additional question with the example you sent back… I’m not able to use the manual index slider to select the curve that lines on the y-axis… do you know why?

(Also, in my real file, I’m not seeing the need to flip to negative distance… the offset on surface node actually fails then…)

It looks like when one curve goes way outside the surface, the grashopper preview becomes unreliable, I’m not seeing curves where there are curves and when you bake them they appear.
Maybe that is the reason you’re not seeing what you expect to see?

Yeah, I do see a lot of weird previews on that offset (and again, I’ve never gotten the negative distance offset to work)…

I’m still getting my pattern that I want in this case, but if I was after those offset lines, I probably would say that this is a bug or at least undesired behavior. The next time I use this Grashopper solution for a different product, I suspect I’ll reopen this thread because it doesn’t seem very robust.