Cancel
Showing results for 
Search instead for 
Did you mean: 

surfacing issue-II

Valued Contributor
Valued Contributor
This is a successor to the previsou thread surfacing issues. Hope to have more of your comments to get better understanding of G2 surfacing.
 
I refined the input splines and rebuit the input faces in the original prt example. Now the issue should be clear and straightforward.
 
Thanks!
 
Image.png
11 REPLIES

Re: surfacing issue-II

Phenom
Phenom

Rather than spoonfeed you steps, why don't we see what you've learned so far?

Here are 2 images from your attachment.  Do you see anything that might be an issue?, particularly with the green and yellow surfaces?

 

snip1.pngPole Structure

snip2.pngKnot / Patch Structure

Some things to consider and/or hints:

  • G2 requires degree 5 minimum yet are there degree 3 splines being used.
  • Why was degree 3 used in the sections but degree 9 used along the guides/rails?
  • Why does the middle surface continue to be created as one large surface?
  • Using a "more user friendly command" like Studio Surface doesn't always equate to lighter surfaces (low degree and low patch count).

 

-Tim

Re: surfacing issue-II

Valued Contributor
Valued Contributor
Hi @TimF   Thanks a lot for your stimulation of thinking!
 
I am sorry to say that I did not understand posts in the previous thread very well. That's why I initiated this thread. Your latest reply, especially your 4 hints, unlock some key issues haunting me since long. Yes. I read @StevenVickers' excellent summary on Continuity vs. Spline degree carefully, but I never considered it seriously enough.
 
Back to the current issue. I adjusted the two Studio Surfaces (green and yellow): "Alignment" from "Arc Length" to "Parameter". All the problems are gone! The "Alignment-Parameter" seems to be the key thing that Studio Surface can do, but Thru Curve Mesh can't do.
 
 
Image.png
 
I would definitely read posts from you and other people in previous threads on this issue again and again in the coming days. It's definitely  another milestone for me in understanding NX surfacing.
 
Thanks to you, @StevenVickers, @Sandman, and @kapilsharma for all your teachings in the threads surfacing issues and refining curve: degree vs. segments!  And my thanks also go to many other people in other related threads!

Re: surfacing issue-II

Phenom
Phenom
@surfactant,

From where I sit, not paying attention to the preferred practices is what has been causing most of your quality issues in this example. These practices aren't etched in stone - you have to finesse these surfaces. It's not easy, either. It's a bit of give and a bit of take. Create, analyze, refine, determine a course of action, recreate. It's usually done in small steps. One practice that won't ever fail you is if you're going for G2, then use degree 5 splines. G1, you can relax a bit and use degree 3 splines.

If your curves are poor, expect poor surfaces.

Ask yourself, is this a surface that looks like it flows well from one direction to another (in regards to the pole and patch structure). If it doesn't flow well, can breaking it into smaller surface patches (pieces) make it flow together better?

Are you happy with the pole structure in the image above? If you are, you need to rethink things a bit, IMO. Getting very close though.
-Tim

Re: surfacing issue-II

Valued Contributor
Valued Contributor
Hi @TimF   Thanks!
 
you have to finesse these surfaces. It's not easy, either. It's a bit of give and a bit of take.
I did make some efforts in refining curves. Those curves might be curves from previous models built by others, edges left by Trim Sheet, or hand sketches. But very often the job seemed to be beyond my capability to handle.
 
Are you happy with the pole structure in the image above? If you are, you need to rethink things a bit
I not not happy with the odd pole structure. Below is one work I did several days ago.
 
  • Refining by Auto Fit (green) is fast and precise, but the resulting poles look odd.
  • Refining by manual adjustment (blue) is painful and rough, but the resulting poles look much better.
 
Maybe the choice is covered by what you meant by "a bit of give and a bit of take".
 
Thanks again!
 
Image.png

Re: surfacing issue-II

Valued Contributor
Valued Contributor

@TimF wrote:

Ask yourself, is this a surface that looks like it flows well from one direction to another (in regards to the pole and patch structure). If it doesn't flow well, can breaking it into smaller surface patches (pieces) make it flow together better?

I'm not sure whether below is the right way of "breaking it into smaller surface patches" or not. The pole structure does look much better.

 

One practice that won't ever fail you is if you're going for G2, then use degree 5 splines. G1, you can relax a bit and use degree 3 splines.

In my understanding, for the current example, "degree 5 splines" are for the guides/rails. I'm not sure whether the sections should also be "degree 5 splines". I 'm not sure whether I understand this correctly or not.

 

Your brief comments would be appreciated!

 

Image.png

Re: surfacing issue-II

Phenom
Phenom

@surfactant,

 

For this instance, I would just use degree 5 all over if it were me. I don't believe I'd ever mix degree 3 with degree 5 in the same areas if I could help it.  The scope of the desired end results should be your guide.  If the desire is Class A, degree 5 is pretty much the preferred choice.

 

The more poles you have, the more the surface should relax as continuity locks down the poles near the ends but the con for high degree splines is the math gets more complicated and "heavier".  We don't want to over do it - degree 7 or 9 at the highest but to be honest, I don't recall what the preferred maximum degree might be.

-Tim

Re: surfacing issue-II

Valued Contributor
Valued Contributor

Hi @TimF  Thanks for the commens on the choice of spline degree! Absolutely helpful!

 

I do want to ask another question. I think I'm a little greedy.  If you think you spent too much time on this thread, please simply pass on it.

 

Very often, one or more input curves are edges left by Trim Sheet, or curves from Combined Projection. Generally they are of bad quality for surfacing. To refine them by Advanced Curve Fit without damaging the model continuity seems to be a big challenge for me. I wonder whether there is a better method to do the job.

 

Thanks again!

Re: surfacing issue-II

Phenom
Phenom

@surfactant,

IMO, the surfaces should be developed such that whether trimmed or not, the result is as needed. This is more than likely why I and others kept stating the root of your original issues were in the adjacent surfaces - they needed to be rebuilt such that they were usable rather than causing more issues.

I feel that if you continue to refine edges with secondary curves, you're potentially going to run into issues sewing the surfaces at some point....just depends on the tolerances and how much your refined curves deviate from the trimmed edges. The more stuff you put between the edges and the end surface, the more tolerance you might be adding into the mix.

Again, you're asking advice based on 3 surfaces - and we all know that's not the entire job, only part of it. To go further, I think we'd need to see the big picture at some point.

-Tim

Re: surfacing issue-II

Gears Honored Contributor Gears Honored Contributor
Gears Honored Contributor

I think the old adage "garbage in = garbage out" was written by someone who did surfacing work for a living. Smiley Happy