Extrude along path - useless?

[Petri Sakkinen]

For the first time I thought I'd need to extrude along path, to get a handrail tube on top of posts that follow a bezier curve in plan and are all on different z-levels.

Well, I can't figure out what sort of objects I can use for this famous feature - everything I try fails because of invalid objects.

Can someone please explain the limitations of the feature?

[Matthew Giampapa]

Path objects can be any linear type object. This includes lines, arcs, circles, polygons, polylines, and nurbs curves.

Profile objects can be any of these except a nurbs curve. (Actualy a nurbs curve can be used as a Profile as well, but it must be flat on the plane.)

The most commong thing that causes a extrude along path to fail is a repeated point along the path, or points along the path in very rapid sucesion.

[P Retondo]

If your path has sharp bends in relation to the cross-sectional dimensions of your profile, the algorithm will not be able to process the calculation because the profile "turns in" on itself while going through your bend. Try using a small diameter circle, or change your path to have gentler curves, to test this answer.

This phenomenon is related to using the "Offset" tool with a complicated polyline. You can get an odd result that "crosses over" itself. AutoCAD, by the way, has programmed around this problem with their offset tool - you always get an offset polyline that has eliminated the cross-overs. Something for NNA to consider - unless the new versions have fixed this!

[ 10-02-2002, 03:34 PM: Message edited by: P Retondo ]

[Petri Sakkinen]

The required path was a 3D poly with six vertices - total length about 10 metres.No close or repeated points, no sharp bends.

The profile was a 50mm circle.

Tried even with a 3D poly with all vertices in the same y coordinates (to make it definitely 'planar.') Tried first converting to a NURBS. Tried a rectangle as the profile.

Nothing worked.

[Guest]

A 3d poly should work.

If you want to email the profile and path objects in one file to us, I can take a look at it.

[Guest]

Wait .. if you used a polyLINE to create the path, then converted that to a 3dpoly, that won't work.

I'll see if I can find out why.

[Petri Sakkinen]

The 3D poly was created with the 3D poly tool - tracing a bunch of 3D loci.

[Guest]

I don't know why it isn't working. If you send it in, I can find out why.

[Petri Sakkinen]

Katie - you are a legend!

(I sent the problem file to her and the solution she provided was to draw a nurbs curve. Conversion treats a 3D poly as a closed poly and there were thus indeed very sharp 'end' vertices.

Conclusion: the tool is useful - if you know how to use it.)

[Daniel Betteridge]

I am not sure if this is off topic but I am trying to extrude along a path a profile moulding that I have imported as a bitmap and then used the trace bitmap command. Vectorworks keeps telling me that I have illegal objects in my selection (A trifle harsh I thought.) Can anybody help me with this as the abilty to inport standard mouldings that I use in my work is a great boon to me

Many Thanks