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# tuning the shape of a spline

Genius
Sometimes tuning a simple spline might turn out to be a big challenge.

Below, I want to create a concave in a small region of a spline. But simply moving a pole affects the whole shape. Maybe the degree of the spline need to be increased to keep the change in a small region. Anyway it seems to be a little complicated.

7 REPLIES 7

# Re: tuning the shape of a spline

Gears Phenom
@surfactant,

That is typical behavior - you've got 5 poles, it's single segment and you're moving one pole near the center of the spline and the end poles aren't constrained for G1 or G2.

Also, if you don't move the other 2 adjacent poles in somewhat the opposite direction to compensate, then you're going to see a shape change like this. The other alternative is to increase the degree, move the pole(s) then decrease the degree before you exit the edit mode.
Tim
NX 11.0.2.7 MP11 Rev. A
GM TcE v11.2.3.1
GM GPDL v11-A.3.6

# Re: tuning the shape of a spline

Genius

@TimF wrote:

The other alternative is to increase the degree, move the pole(s) then decrease the degree before you exit the edit mode.

It's unbelievable that the spline almost maintains its adjusted shape when its degree is decreased again to the original value.

Awesome technique! Perfect! Thank you!

Hi @Yamada, you might be interested in why the technique works in mathematics.

# Re: tuning the shape of a spline

Gears Phenom

@surfactant,

Please double check that the spline is maintaining what you expect, mainly number of segments. I always check that box (if it's what I desire, which is most of the time) just to be safe.  Studio Spline is a really cool command - you can switch many things around - see the attached movie below for an example of what I like to do from time to time - start with the end points then add poles and come back to shape the curve.

The main point is that you're going to have to adjust the adjacent poles, regardless - increasing the degree just means you may have to move them a bit less.

Splines can be tricky, but I try to make it simple by thinking that I can either increase degree or segmentation to control the general shape - continuity constraints will also restrain pole/point movement. The more control you desire, the more difficult it can become the achieve a specific shape.

Tim
NX 11.0.2.7 MP11 Rev. A
GM TcE v11.2.3.1
GM GPDL v11-A.3.6

# Re: tuning the shape of a spline

Genius

@TimF wrote:
Splines can be tricky, ...

Absolutely correct! You are tremendously helpful. Thank you for you comments and workflow illustrated in your video!

# Re: tuning the shape of a spline

Honored Contributor

@TimF wrote:

The more control you desire, the more difficult it can become the achieve a specific shape.

That should be on a t-shirt or something.  A very hard concept to instill.

-Dave
NX1867(if it had versions) | Teamcenter 11.6 | Windows 10
Highlighted

# Re: tuning the shape of a spline

Gears Phenom
@DaveK,

What made the light bulb come on for me was when I compared the behavior of a spline created with Through Points vs. a spline created By Poles. I find the spline By Poles to be much easier to shape for me, I've rarely ever had a specific need to have a spline pass through a set of specific points - I've normally had the freedom to drag the spline somewhere close to the shape I've needed. If the spline HAD to go through points, I typically (visually) fit lines and arcs close to the spline and used those instead.
Tim
NX 11.0.2.7 MP11 Rev. A
GM TcE v11.2.3.1
GM GPDL v11-A.3.6

# Re: tuning the shape of a spline

Honored Contributor

Exactly how I do it, but the engineering mind is usually focused on exact specifics, and not really really close visually.

-Dave
NX1867(if it had versions) | Teamcenter 11.6 | Windows 10