Author Topic: closing a bezier curve?  (Read 308 times)

davidorth

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closing a bezier curve?
« on: April 25, 2017, 07:08:40 AM »
I'm drawing a classic modern style coffee table with a boomerang shape top.  The bezier curve is working great, but I get a bump where the first and last point meet. On the other hand the simpler "curve" function will automatically create a fair curve through the first and last point of a line if they are on top of each other.  Can I do the same with the "bezier curve" function?

I can try to visually fair out the curve through this first and last point, but just wondering if there is a way to join and close the loop so it is automatically fair.  Perhaps even a work around idea would be helpful.  The guide points for the bezier define tangent lines.  If my guidelines for first and last point were on the same line through these points seems like I could get something approaching a fair curve through these points.  Not very user friendly though.

Anyone figured this out?

Rob S

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Re: closing a bezier curve?
« Reply #1 on: April 25, 2017, 07:51:08 AM »
You could try placing the last two points on top of the first two points.   The curve seems to close smoothly for me then.

In other words, for the second to last guide point of your curve, snap to the first point you set, and for the last point snap to the second point, and then press enter to finish.

Once you have completed your curve you can fins tune it by adjusting position of any of the points using "point select mode"
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davidorth

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Re: closing a bezier curve?
« Reply #2 on: April 25, 2017, 08:33:53 AM »
Good idea.  Thanks.  That puts the first and last tangent control points on top of each other guaranteeing the fairness.  However, I think I would usually want to edit the distance of each of these tangent control points  separately to achieve the shape I want - keeping them on that tangent line but adjusting the distances separately to separately control the character of the line coming in and out of that node.  It appears however, that point select mode grabs both these points and you can't adjust them separately.  My boomerang is assymmetrical and I need this.

You can draw a temporary tangent line through this beginning/ending point.  Then edit the control points so that they lay anywhere along that one tangent.  The line will be fair then no matter how you drag that beginning/ending point around.  And you can control the curvature of the line coming in and out of that node separately.

If the two tangent control points are not on that same tangent, then editing the shape by grabbing the beginning ending point maintains a "bump" or lack of fairness relative to the original control points.  Makes sense, you don't always want a fair line at this point.

I like initial speed of your approach.  If I weren't needing to control the exact character of the line coming in and out of that point, then the work would be done.

Thanks much.

Rob S

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Re: closing a bezier curve?
« Reply #3 on: April 25, 2017, 08:53:48 AM »
It seems to me the line coming out in both directions is also controlled by the distance between adjacent tangent points, so you should be able to adjust that by adjusting the spacing of those tangent points.

You could also place the beginning/ending point in a smooth section of the curve.
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davidorth

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Re: closing a bezier curve?
« Reply #4 on: April 26, 2017, 08:34:44 AM »
Thanks, Rob, this discussion has clarified my problem and given me a satisfying, general solution. 

Restated, I would say that if you want a completely fair enclosure with the bezier curve, then just make sure the first and last tangent control lines are lined up through the beginning/ending point.  Easiest for me to set these as best I can visually, then draw a temporary tangent line through that beginning/ending point and edit the two adjacent tangent controls so that they are on that line at whatever distances give you the curvatures you want on either side of the point.

Something like this should be added to the manual.  I have no idea how hard it would be to create a fair and closed version of the bezier curve function that would solve this problem and give us easy ways to edit the location of the beginning/ending point without undoing the fairness.  Such a command must force these two adjacent tangent controls to rotate together about the beginning/ending point keeping them on the same line.  And if the beginning/ending point is moved the adjacent tangent controls would have to move with it.

I think.  Best regards.