Definition of a Ruled Surface

[VitaminM]

What is the exact definition of a "ruled surface"?
I am writing procedures for my company and I need to inlcude this.

I know what it is as far as equally spaced points along two splines and direct lines between them and so on, but it would help if I could get the exact verbage.

I couldn't find a good definition anywhere. Not even in the NX4 documentation.

(and for my own curiosity, how is this different from a Through Curve Mesh, which sounds like the same thing)?

 

[cowski]

A ruled surface will only have curvature in 1 direction ("direct lines between them" as in your description); through curves and through curve mesh allow you to have curvature in 2 directions (u and v).

 

[JohnRBaker]

Well there's a Wikipedia entry for Ruled Surface at...

http://en.wikipedia.org/wiki/Ruled_surface

...with several good examples.

As far as how does a Ruled Surface differ from a Surface Through Curves, it actually doesn't, as long as you only select 2 curves and use the same Parameterization options and tolerances. In fact, there was a proposal a year or so back, which has been temporarily deferred, that we obsolete Ruled Surfaces and just recommend that our customers use Surface Through Curves for all of their surface creation needs when there are only primary and no cross curves (of which a Ruled Surface is a special case of this situation).

Anyway, I personally have simply hidden Ruled Surface and have now only use Surface Through Curves for this type of surface.

John R. Baker, P.E.
Product 'Evangelist'
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Siemens PLM Software Inc.
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To an Engineer, the glass is twice as big as it needs to be.

 

[hudson888]

There's a lot of it about. That is knowing how the tools more or less work without knowing too much about what it is that they actually do. I have met people who on encountering these concepts rushed straight out to purchase books about Bezier mathematics.

I guess that there are a couple of ways of coming up with a definition of a ruled surface. You could work your way back from a more complex definition to say that it is a mesh surface with only two primary sections and no defined cross curves so that the sections are presumed spanned by a degree one shape.

Unless you really want to delve into the mathematics of curves which are the gateway to understanding all B-Surfaces as matrices defining the mesh of the surface then you're safe enough knowing that most freeform surfaces are mathematically similar the only difference being the amount of complexity. That would be expressed in surfaces as degree and number of patches much as in curves it is expressed in degree and number of segments.

As John says the through curves surface when defined similarly is a ruled surface for all intents and purposes. You won't create two surfaces in the same way using either tool and find any differences. However I'd also add that by using through curves surfaces you can spin off in a different direction when selecting two curves and by imposing continuity make some different assumptions about the nature of the cross curves, and when you do that you're not making a ruled surface any more.

Anyway I hope that helped!

Best Regards

Hudson

www.jamb.com.au

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