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# skew a spline

Genius

Is there any easy way to skew a spline? Currenly I build sophisticated constraints in sketch to do this job. It's really a painful process.

Thanks!

4 REPLIES

# Re: skew a spline

Siemens Phenom

You could do this using the Global Shaping function, maybe, with the By Surface option. Basically, skewing is an operation that turns a rectangle into a parallelogram, so these are what you use for your base surface and control surface respectively.

The problem is that Global Shaping doesn't seem to work on curves, so you'd have to build a little fake surface from your curve before applying Global Shaping.

This is really using a sledgehammer to crack walnuts, though. If I had to do this often, I'd just write a little Skew function using NX/Open or SNAP. You let the user specify a skew angle, theta, and a fixed point (x0,y0), and then you move the spline poles according to the formula:

```xnew = x0 + (y - y0)*tan(theta)
ynew = y```

This skews the spline to the right by an angle theta, and the point (x0,y0) remains fixed. About 10 lines of code if you use SNAP.

# Re: skew a spline

Genius

Hi @Yamada   Thanks for the solutions!

I'm deciding whether to spent time to learn something about SNAP. I have a fundamental question:

• If I write a piece of code in SNAP to do the skew job, does it work like a new feature that can be associative and listed under Model History?

# Re: skew a spline

Siemens Phenom

Unless you do some extra work, you get a "dumb" spline.

There is a "Custom Feature" capability that will let you create a new feature that behaves more-or-less like the built-in ones. If you used this technology, you'd get a "Skew" feature in the Part Navigator, and you could edit its angle parameter.

However ...

1. It's not supported in SNAP, yet, so you have to use NX/Open, too
2. It's a fairly advanced topic, and not a good project for a newbie. That will change if/when it's supported in SNAP
3. It's pretty new, so it has some rough edges
4. Very few people have experience with it, so expertise is scarce

But, if you like the bleeding edge, feel free to jump in. I'd be interested to know where you have problems, because I'd very much like to make it easier for people.

# Re: skew a spline

Genius

Hi @Yamada   Thanks for your information! If the SNAP code gives only a "dumb" object and "Custom Feature" is a big project, I think that I would simply use the Global Shaping, although a sledgehammer for a walnut. Thanks again!