spline handles

[anita.neilson]

can you move just one spline handle on the side of a point?  When i try to both handles always move. I only want one to move. 

[jeff_strater]

Yes, you are correct - today, Fusion spline handles are symmetric - you cannot drag just one side of a spline handle.

Jeff

[anita.neilson]

****! Will it change anytime soon?

[Anonymous]

I agree that this is a frequent problem for me also and seems to prevent me from doing some things that I want to do.

[PaulMunford]

Why do you only want one side to move? What would you like to happen?

[laughingcreek]

The OP probably means they would like the influence of the curvature to be different on each side of the point, like in the pic.  (the pic shows a work around where 2 different splines are used instead of one.  The advent of the smooth constraint makes this better than the old workaround using collinear on the spline handles)

[clint]

Completely agree about asymmetric spline handle control.  Use any other software (2d or 3d) with bezier curves and you can do this.

Right now I'm trying to trace a part and finding it impossible because the curve coming out of a point is not the same as that going into the point.

[TrippyLighting]

Here is a link to an article explaining how Splines are implemented in Fusion 360. It might also explain why the 2 sides of Spline handles cannot be manipulated independently.

After all B-Splines and Bezier Splines are related, but not the same. Most implementations I've seen where handles can be manipulated independently are Bezier Splines.

Most CAD software including Autodesk Inventor and Fusion 360 work with 3 degree surfaces NURBS or Non Uniform Rational B-Splines.

[TrippyLighting]

@laughingcreek the smooth constraint provides G2 surface continuity. Making the spline handles collinear is only G1.

[chrisplyler]

If you use separate splines with a common endpoint location... You can get the same results as you can in other software using Bezier curves (such as Adobe Illustrator) by converting a point such that its control handle can have either side manipulated independently. That result is a corner, or a G0 continuity.

If you then make the two control handles Tangent or Collinear to each other, that result is instead a curve that is smooth at least AT the common point, or a G1 continuity.

If then, in addition to the Tangent of Collinear constraint, you add an Equal constraint or otherwise force both handles to be the same length, that result will now be smooth AT the common point AND have the same rate of curvature change moving away from the common point, or a G2 continuity.

IF IF IF you want that G2 condition, then there is no reason to use two splines in the first place, or, in the case of Adobe Illustrator or the like, no reason to have converted the point.

[chrisplyler]

Oh...

If you take any two sequential points along a spline, and make their control handles Equal or otherwise force them to be the same length, I pretty sure that makes the curve between them G3.

[Inspections_JCH]

Remember that the Smooth Constraint is now named the Curvature Constraint.

[TrippyLighting]

Thanks, I had not even noticed that. Once you are used to pick and click on a symbol often you don't look at the text anymore. I wish they would put the common nomenclature G1 and G2 there, but ...

[Anonymous]

I would also like to see single-handle adjustment. Adobe Illustrator and Affinity Designer, just to name a few drawing programs allows that. I have struggled to trace lines in embedded drawings (canvas) and having the opposite handle fight me when a curve is needed on one side of a control point and a straight line is needed on the other side. I suppose there are other ways to draw this but I find single-handle adjustment very useful!

[chrisplyler]

In Illustrator, for that functionality, you have to convert the point into a corner. The equivalent functionality in Fusion just ending one spline and beginning another on the same point, which isn't as useful because you can't go back and decide to convert it after the fact. You have to know where you want your corners in advance, or you will be stuck redoing it all from scratch.

[TrippyLighting]

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@chrisplyler wrote:

Oh...

If you take any two sequential points along a spline, and make their control handles Equal or otherwise force them to be the same length, I pretty sure that makes the curve between them G3.

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Interesting. Never seen this comment. It's incorrect though and can be easily tested.

The spline handles here are of equal length and colinear and this isn't G3.

However, you can make splines with G3 curvature continuity using 5-degree control point splines. The usefulness of that is limited.

 

 

[chrisplyler]

Ah. I can't think of why I would have said that now. Thanks for the correction.

[raymondcat0125]

Ugh I was hoping the spline tool had the same functionality as the photoshop pen tool. Where you have the option to move handles independently to easily manipulate paths (shown in photo). Its whatever though, there are ways around it.

[matthewrjacobs]

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@raymondcat0125 wrote:

Ugh I was hoping the spline tool had the same functionality as the photoshop pen tool. Where you have the option to move handles independently to easily manipulate paths (shown in photo). Its whatever though, there are ways around it.

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They do,  if you click on the spline you should see green handles for a fit point  spline, and orange construction line handles for CV splines.   if you want a control handle in the middle of the spline you can right click on the spline and select add control point.

The second picture will require two separate splines to produce.