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Cannot "close" curve

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Daniel Hybiak
Cannot "close" curve
on Mar 1, 2013 at 6:31:32 am

Hey guys,

Simple (hopefully) question:

I'm using a bezier curve to trace out a shape from an image plane. From there, I want to duplicate and mirror the curve (since, in the reference, I can only see half the shape anyway), combine the two, and close it off so the entire shape is one, connected curve.

I can't figure out how to fully close the curve off though, and still have a part where there are two CVs just directly on top of one another.

Here's the process I did to get to where I am now, if it helps:

1) trace half the shape using bezier curves
2) Snap the first and last points of the shape to a grid line, so they share the same X coordinate
3) duplicate the curve, and invert the duplicate by changing scale X to -1
4) apply "reverse curve" on the duplicate
5) select both curves, apply "attach curves"

This ends up joining the bottom two points, but not the top two.

Any advice would be greatly appreciated. I've attached an image of the situation. The top point is where the curve is not connected.

On a side note: am I even using the right term (close)? I've read about open, closed, and periodic curves...not sure which one I'm trying to make, lol. The idea is to have no gaps.

Thanks! =D



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Daniel Hybiak
Re: Cannot "close" curve
on Mar 1, 2013 at 8:47:26 am

Ok, did more reading on this topic, and a lightbulb went on. So here's the question more succinctly (I think):

How can I change a "closed" curve into a "periodic" curve?

;) yay for learning!


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Daniel Hybiak
Re: Cannot "close" curve
on Mar 1, 2013 at 10:26:34 am

Lol, alright, after a long bout of reading into the math behind curves, the definitions, etc., it appears as if there IS no way to make B├ęzier curves periodic. However, with conversion to a NURBS curve, there might be some method. Regardless...I'm not going to worry about it. If somebody has an answer though, please post it!


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Steve Sayer
Re: Cannot "close" curve
on Mar 1, 2013 at 7:58:57 pm

Hi Daniel.

I'm afraid I haven't done any work with Beziers in Maya... you're right that it seems the 'Periodic' option is only available for NURBS curves. However, doing a quick test, even converting a Bezier loop like yours into a periodic NURBS curve left me with two CVs overlapping at the seam... and deleting one of them makes the seam jump a step to the side. Odd behaviour; not quite what I was expecting.

What are your plans with the curve? Why do you need to create it with Bezier tools, but also need it to be periodic when you're done? Perhaps we can find you another workaround.


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Daniel Hybiak
Re: Cannot "close" curve
on Mar 2, 2013 at 12:47:43 am

Hi there,

Honestly, the more I've investigated this, the more I'm realizing its ok to have a standard "closed" curve for use when extruding. I was initially getting hung up on the idea that unless it was completely closed, i.e. no way to pull it apart at the points, then my extruded shapes would eventually be messed up or something because they wouldn't be connected. However, when testing this further, they seem to be ok.

It's just a strange concept to be I'm getting used to, the idea of a curve that can act as a "mold" per se for extruding or lofting, but is not itself truly closed and is easily pulled apart. I imagine it like a string, and if the string has a cut in it, anything I try and do with it, it will just fall apart. Apparently that's not necessarily true.

:) thanks for your help though in looking into this as well. I really appreciate it!

And I definitely have other maya questions I'll be posting about, lol.

-Dan


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Steve Sayer
Re: Cannot "close" curve
on Mar 4, 2013 at 3:05:23 pm

Yeah, it seems to be okay. Even with an 'Open' Bezier loop, an extruded polygon shell or NURBS surface will be correctly 'sealed' all the way around.

Glad it worked out.

Edit: Meant to add... some strategies for testing the 'watertightness' of extruded surfaces:

* Select the surface and hit '3' to smooth the display of it. If there are overlapping edges that aren't sealed, they will shrink away from each other, exposing a gap.

* Click to select an individual vertex or CV, and move it. Do NOT select by click-dragging a box, as that will select multiple vertices or CVs if they overlap each other. A single click will always pick up only one point. Once you have one selected, just move it around and see if that opens up a hole, or the surface stays continuous.


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Daniel Hybiak
Re: Cannot "close" curve
on Mar 7, 2013 at 6:30:31 am

Awesome, I'll do that from here out :)


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