difference birail sweep (loft) and revolve with rail

[Bas Vellekoop]

What is the difference in use between these two?

And why does een birail sweep create 2 separate nurbs surfaces?

Is it possible to combine these 2 nurbs surfaces so its possible make it part of a surface array? (because its not possible two add 2 base surfaces in a array)

Edited April 4, 2014 by Buzz Lightyear

[PVA - Admin]

In that example, no difference. They are both two completely valid methods you could use to create that shape.

Revolve with Rail is designed to have an axis and swing two profile curves around it. Useful for creating circus tents and oddly shaped roof elements and other cap-like objects.

Birail sweep can do a lot of what revolve with rail can do, but its a little more free in what kinds of profile curves can be selected and can create long flowing tunnel-like shapes that revolve with rail could not accomplish:

To Combine the two NURBS surfaces with matching edges you can normally select both, then use Modify > Compose. Sometimes if the edges aren't exact you can use Add Solids to get a Solid Addition instead.

Edited April 4, 2014 by JimW

[Kevin McAllister]

Jim, I tried building a similar shape to the original poster. I couldn't get Compose to join the surfaces. In fact, I don't think I've ever gotten Compose to join two surfaces. Is it looking at more than the shape of the curves (ie. does it look at the shape of the surface as it approaches the join)? I suspect the same reason why they won't compose is why it generates two surfaces to begin with.

Another reason for the seams may be because VW can't generate closed NURBS curves as far as I know. If you convert a circle to NURBS and then click to edit the points there's always two overlapping points. This means the source curves have seams. Revolve with Rail may have a way to reconcile a "closed" curve much like sweep understands a 360 sweep as a closed object.

Kevin

[PVA - Admin]

Forgot another possibility, with both surfaces selected, you can also use Model > 3D Powerpack > Stitch and Trim surfaces, it is a little more lenient as to what it will allow before performing the operation.

[PVA - Admin]

Another way you can try to get solids out of surfaces, you can use Model > 3D Power Pack > Create Planar Caps. It will attempt to create surfaces to cover over any holes between edges of the selected NURBS surface.

It will often make way too many surfaces as a result, but then this group of surfaces can usually be ungrouped and then Stitch and Trim will make them a generic solid, which can be Add Solids-ed to the original surface to create your solid object.

(However I am sure there are less messy ways most likely, I am shown up regularly by some of the 3D modelling experts here on the boards.)

[Bas Vellekoop]

I want it to stay 1 nurbs Surface so i can use it in a surface array. (Its a shame you cant use several nurbs sarfaces in a array.)

[Benson Shaw]

Buzz - If you know the top, bottom and at least one intermediate curve, a simple Loft Surface, clicking each curve eg bot to mid to top, can create a continuous NURBS Surface. Shape and Z value of the middle curve control curvature of the surface.

-B

[Bas Vellekoop]

Thanks for the tip!

Would love to see everthing out of this topic in Vectoroworks.

http://techboard.vectorworks.net/ubbthreads.php?ubb=showflat&Number=195969&Searchpage=2&Main=38106&Words=nurbs&Search=true#Post195969

I would be great if the loft tools worked like in C4D

Edited April 9, 2014 by Buzz Lightyear