Hi PaQ, yeah for NURBS a tube is a pretty complex object, mostly because of the focus on accuracy. The polygon tube will have some pretty substantial (as far as tolerances go) deviations in parts of its "surface" (facets) from the pure tube... With the NURBS sweep that surface is repeatedly subdivided until it has accuracy of 0.001 units from the "perfect" tube. The bulk of the time is in that refinement process and repeated tolerance checking. Poly modeling just pretty much skips all that tolerance testing.

Anyway - re: offset -

You don't have to do sweep with the rails only running directly through the center point of a profile.

If you place the circle so that it touches the rail only on one side like this:



Then when you sweep it, it will not be moved to the center, it will take the profile from where it stands and drag it along the rail:




Does that produce the kind of offset tube that you are looking for?

If so then you just kind of carefully position 1 circle to that orientation at the end of a curve and you're done... Don't use the auto-place mode for this, because auto-place will put it with the profile centered right on the rail.


re: Offset from surface while drawing - one way you can possibly do that now is to drag out a construction line on the surface normal before you place the point. You may need to do a little slight of hand to type in the distance before you finish the construction line to place the end at the distance you want. A kind of "running offset distance" is an interesting idea but may be somewhat difficult to set up, a surface normal has 2 directions on it and it may be difficult for you to predict which is the "positive" side on any given free-standing surface. So just setting a single value and then doing single pick, pick, pick after that probably would not do it properly, you would need to do something like 2 picks with the second pick indicating which side... Might be rather awkward to set up.


Anyway, does positioning the profile circle at the offset location work ok for what you need?

- Michael