topic Re: T-Splines Tangent Handles in Fusion Design, Validate & Document Forum

T-Splines Tangent Handles

felix_star — Thu, 18 Sep 2025 20:28:14 GMT

Hello everyone!
T-Splines are potentially a truly amazing technology! You can create shapes that are difficult to achieve with other CAD systems, even with just tangent handles! 😉 Unfortunately, they're very very difficult to manipulate: you can't enter numerical values for precise point placement, and snapping doesn't work very well either... 😕 I suggest to the development team pay more attention to these tangent handles because they're very very useful to design perfect shapes! 😉
Bye,

Felix 😉

Re: T-Splines Tangent Handles

adam.helps — Fri, 19 Sep 2025 17:11:09 GMT

Thank you for the suggestion. I understand how numeric input would work for tangent handles. I also understand how snapping would be useful for control points. I am wondering in what situation you'd expect tangent handle snapping to be useful--could you go into a little more detail on what you expect that workflow to look like? I want to make sure I've understood what you are trying to achieve.

Re: T-Splines Tangent Handles

felix_star — Sat, 20 Sep 2025 10:36:13 GMT

Hi Adam and thanks for your reply!
I've prepared an example with one of the most difficult shapes to create with CAD systems (without using trimmed surfaces, thus accepting tollerances...): the famous "Y branch" shape. T-Splines technology can solve this problem without having to trim the surfaces. Many CAD systems have introduced Sub-D, but none have the same capabilities as T-Splines, first for the T-junctions and then for manipulating the tangent handles (in other CAD systems, the curvature at the edges always goes to zero, even when you don't want it!). I've attached the workflow sequence using some files. Finally, when I want to achieve G2 continuity also towards the straight part of the Y-branch (joined and patched T-Splines), I can't manage the snapping (edge surface points and tangent handles) to any line or point... 😕
Kinds,

Felix 😉

Re: T-Splines Tangent Handles

felix_star — Sat, 20 Sep 2025 11:41:03 GMT

I'm attaching the file "T-Spline Y branch 10.f3d" because I suceeded to achive what I wanted, following another way: T-Splines are great! But I still think that is necessary to improve the capabilitues to manipulation of the the tangent handles. I challenge any other CAD system to do the same with their Sub-D. If you look well, the top and bottom are perfectly planar! This is not possible with the Sub-Ds of other systems... 😉

Felix 😉

Re: T-Splines Tangent Handles

TrippyLighting — Sat, 20 Sep 2025 22:50:18 GMT

I believe the capabilities you are seeking (proper curvature and better control) are already present in Autodesk Alias, where the T-Spline technology was used to achieve such things. Don't get sidetracked by the "Subdivision" terminology.

Unfortunately, the insane price point puts this out of reach of mere mortals.

Re: T-Splines Tangent Handles

felix_star — Sun, 21 Sep 2025 08:06:20 GMT

Hi Trippy, thanks for your message!

I tried the educational version of Alias, but I don't remember these features. I think T-Splines were only used for SpeedForm for Alias.

Felix 😉

Re: T-Splines Tangent Handles

adam.helps — Tue, 23 Sep 2025 17:37:31 GMT

@TrippyLighting Alias is doing something interesting. They are using T-splines, but they don't allow T-points, tangency handles, or non-uniformity (effectively using the T-spline as a subd model). To manage tangency, they instead have a more complex crease system that allows for various sliders to control the crease's behavior. I believe that lets them do more than a typical subd crease, though I don't know enough detail to say exactly what the capabilities are. So it's technically T-splines minus some capabilities but then with some other capabilities layered on top.

Re: T-Splines Tangent Handles

TrippyLighting — Tue, 23 Sep 2025 17:51:12 GMT

@adam.helps wrote:

@TrippyLighting Alias is doing something interesting. They are using T-splines, but they don't allow T-points, tangency handles, or non-uniformity (effectively using the T-spline as a subd model). To manage tangency, they instead have a more complex crease system that allows for various sliders to control the crease's behavior.

The way I interpret that is they have a weighted crease!
Can you confirm that?

I would love to have a weighted crease in Fusion T-Splines!

Re: T-Splines Tangent Handles

felix_star — Wed, 24 Sep 2025 19:58:16 GMT

Hello @TrippyLighting, but do think is so important to have weighted creases when you can obtain, more or less, the same thing adding edges to the polygon cage? 😉

Re: T-Splines Tangent Handles

TrippyLighting — Thu, 25 Sep 2025 01:18:47 GMT

I like options!

I very often model with weighted creases in Blender, as it allows me to judge the final form while still modeling.

Adding edge (support) loops adds geometry, which makes modeling very cumbersome.

Changing the weight of a crease is much quicker than sliding edge loops.

When I am happy with the overall shape, sometimes I replace the weighted creases with edge loops.