topic Control Point Spline end point in Fusion Support Forum

Control Point Spline end point

krauken — Thu, 02 Jul 2020 15:11:17 GMT

I'm not sure if I'm not doing this right or it's just not possible in Fusion, but I can't seem to figure out how to make control point splines to be "tangent" when the end point is also the start point (closed loop). Is this not a supported feature?

Re: Control Point Spline end point

jhackney1972 — Thu, 02 Jul 2020 16:22:33 GMT

In this sketch, add a construction line between the first and last control points, then add a coincident between the beginning (ending) point and the construction line. That should do it for you. You would probably have better control using a Fit Point Spline.

Re: Control Point Spline end point

krauken — Thu, 02 Jul 2020 16:36:52 GMT

Okay. If I were to reposition that end point though, it would break the curvature, right? I've managed to make my spline using the fit point spline. Is this shape basically not possible with control point because its 100% curved at all points?

Re: Control Point Spline end point

jhackney1972 — Thu, 02 Jul 2020 16:48:24 GMT

Why do you not try it for yourself? Because of the Coincident constrain, the beginning ending points cannot leave the construction line. You also could simply add a Parallel constrain between the first and last control point construction lines and not even sketch an extra one. The same is true for a fit point spline. The beginning and ending points automatically have an instantaneous tangent.

Re: Control Point Spline end point

krauken — Thu, 02 Jul 2020 17:30:18 GMT

I have indeed tried this myself, and it's not behaving as you described, which is why I'm asking on here 🙂

So when I use the control point spline, and connect my end point to my beginning point, it does not create a "automatic instantaneous tangent." It does with the Fit Point Spline which is nice, but not with the Control Point Spline which is the type I'd really prefer to use if possible.

I do not want to create a construction line because this is an organic spline shape that has no straight edges and points need to be able to be modified freely in all axes.

I am able to add a parallel constraint to the first and last construction point lines as you said, which of course makes the spline tangent in this area, but now I lose the control ability to artistically modify the shape of the curve in that area.

See attached image for what I would need Fusion to do to allow me full control of the spline edits. If this isn't possible, I'll just stick with Fit Point for now 😕

Thanks for your help btw!

Re: Control Point Spline end point

jhackney1972 — Thu, 02 Jul 2020 17:33:45 GMT

Unless you get lucky, when you sketch a Control Point Spline, you will not get the same "instantaneous tangency" you get at the beginning, ending points of a Fit Point Spline without adding some sketch constraints to the beginning and ending control points. So if you have to have this condition, you will have to use the Fit Point Spline. The handles of a Fit Point Spline give you good control if you use them correctly. They will accept sketch constraints and dimensions to influence the spline.

Re: Control Point Spline end point

jhackney1972 — Thu, 02 Jul 2020 17:39:48 GMT

You do have an option of right clicking on the Control Point Spline and adding a control point very close to the beginning, ending point to achieve a close "instantaneous tangency" that will still allow you to move the other control points as needed.

Re: Control Point Spline end point

krauken — Thu, 02 Jul 2020 17:56:59 GMT

Okay, sounds like it's just not how the tool can work in Fusion. I'll stick with fit point for this shape.

I really think it would be very easy to implement this feature since computing control point splines is very similar math to how subdivided mesh assets are controlled with a 3d low poly cage, essentially what the T-splines are. Do you know if there is a proper place to suggest this where it will actually get seen by devs? My 3d modeling background is in sub-d modeling in Maya for highpoly assets for video games, and working with a control point style manipulation is fantastic compared to fit, imho.

Thanks for the help John! 🙂

Re: Control Point Spline end point

jeff_strater — Fri, 03 Jul 2020 00:41:24 GMT

can't you just make the start and end control construction lines colinear? Doesn't that do the trick?

Re: Control Point Spline end point

krauken — Fri, 03 Jul 2020 01:08:33 GMT

Technically, yes, but as stated above locking those two lines together (be it parallel or co-linear) now takes away the ability to manually move each point individually to control the shape which is the entire point of using a spline to create an organic shape, which in my case, is something I would like to have complete control over. The point is to keep free-form control of the spline, not lock aspects of it down and attempt to work around that constraint.

This is what I would expect when ending the spline on the start point, just like the other spline tool does.