Hi Steve,

> I have made some more closed 2 rail sweeps and they are
> producing edges with gaps as with the first model and
> causing the same problem.

Could you show me one? I displayed the objects with Style = "sweep" from your example above, and did the sweep and I get closed edge curves on the sweep result.

As far as I can tell in your example, the edge that you are offsetting did not come directly from the sweep, it seems to be the result of a fillet or something like that.

- Michael

Hi Michael,

Offsetting the surface (from 2 rail closed sweep) edge.

Hi Steve,

> Offsetting the surface (from 2 rail closed sweep) edge.

Yup, that's definitely another instance of that same offset problem.

I don't see any gaps in the edges there though, in a message above you wrote that you were seeing edge gaps in some closed sweeps? This does not seem to be an example of that, the edges are closed with no gaps.

Sorry if I confused things with mentioning the gaps - the gaps are not actually what causes the offset problem, I mentioned the gap only because it was what created the difference in behavior between v1 and v2.

This particular offset problem will actually _not_ be present if there is a gap, that's why you don't see it in your original example with v1, because v1 does not automatically seal the gap into a closed curve during the offset. It's actually with a closed curve where the offset bug is kicking in. In v2 it is automatically sealing that little gap up to make a closed curve, that's why there is a difference between v1 and v2.

V1 actually still has the same offset bug in it, just different behavior with sealing the little gap up.

- Michael

Hi Michael,

On my first model, yes, sorry, my error is description of construction and what I used.

I made 2 rail sweep, then used planer to create solid. I attempted to add a small rad on that top edge but could only get a rad as small as 0.5(or 0.4). so I separated the surfaces then used the 2 top surfaces to produce the rad. I then tried to used the top of the rad produced to offset.


- Steve

Also since your new example actually does not have any gap, you can repeat the offset problem in v1 with it as well.

The only reason your original one did not repeat the problem in v1 was because it had that little gap in it.

- Michael

Hi Steve,



Right, so that edge with the little gap in it was not produced by sweep, it came from fillet.

It looks like the filleter wasn't able to make a completely great fillet surface there, if you separate it out and untrim it you can see the fillet surface itself actually has that gap in it.

So as far as I can tell there is nothing wrong with the sweep command there, it was a problem with fillet.

I think in v3 I may add some processing to automatically seal up curves for edges that are topologically closed like this.

- Michael

Hi Steve, also with your new example the same technique I described earlier of splitting the curve up at some other point will make it offset properly.

I've attached an example here, with the edge split up at one other point. Now you can select the 2 edges and use offset on them and get an expected result in the particular zone where it was previously going crazy.

- Michael

Hi Michael,

>>So as far as I can tell there is nothing wrong with the sweep command there, it was a problem with fillet.<<


I find it strange that after I make the 2 rail sweep in Rhino, the fillet can be made in MOI. There is something not right here.




- Steve

Hi Steve, probably it's some difference in the tangent directions at the ends of the sweep between the Rhino one and the MoI one.

It is possible that Rhino does a better job ensuring that the end tangents on a single closed surface sweep like that are exactly in line with one another.

- Michael

Hi Michael,

I will have to be cautious or avoid these types of closed sweeps in MOI.


- Steve