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perplexing "Advanced Curve Fit"

Valued Contributor
Valued Contributor

I have a Combined Projection curve in the early stage of my model. To improve its quality, I enabled Advanced Curve Fit function.

 

When I zoomed the model big in the later stage, I sadly found that Advanced Curve Fit introduced a disastrous inflextion point to the curve. This makes me greatly concerned about use of "Advanced Curve Fit".

Your comments would be appreciated. Thanks!


Advanced Curve Fit disabled (partical curve)

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Advanced Curve Fit enabled (partical curve)

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4 REPLIES

Re: perplexing "Advanced Curve Fit"

Siemens Legend Siemens Legend
Siemens Legend

Hi @surfactant!

 

Sounds like you are making the assumption that use of Advanced Fit = Better Quality.

 

Maybe, maybe not.

 

Advanced Fit really just gives you finer control over some of the low-level Math that defines the curves.

 

So some general rules of thumb I use with customers:

 

1) If you don't understand all the Math, you probably don't want to be messing around with this, unless you are just playing around and/or not too concerned about the details (like the detail you found). You are better off allowing the software to make those decisions for you.

 

2) In general "complexity" and "smoothness" are at odds with each other, and "simple" usually gives the best result. The Advanced Fit allows you to really drive up the complexity and therefore can be at cost of Smoothness.

 

Not knowing the exact settings you have, your geometry, or end goals, hard to give further specifics.

 

But I would not put the blame on the Advanced Fit; it's likely doing exactly what you asked it to do; you probably just don't want to be asking it to do that :-)

 

Pat

Re: perplexing "Advanced Curve Fit"

Valued Contributor
Valued Contributor

Hi @PatMcManus   Thanks for your explanation! I'm not blaming Advanced Curve Fit. It simply refits the curve with parameters specified by users and is not responsible for any kind of misuse. I just come to know that refining curves during the modeling process need to be very very careful.

Re: perplexing "Advanced Curve Fit"

Siemens Legend Siemens Legend
Siemens Legend

Yep. It's a tricky thing.

 

I saw after I posted that you had a couple of related discussions earlier on Surface fitting and such, and input from Steve and others. That advice applies here as well.

 

I helped give some training classes years back to Auto Class A Surface users, and the trainer was an expert who had worked in the industry for years. Part of the training was learning to fit very smooth, lower order surfaces, with a minimum number of patches, through millions of scanned points, and still get great highlight lines.

 

As he explained things, it all seemed "obvious" as he showed and explained, but doing it in reality, without all his experience, or trying to explain to someone else, since I've never really done real work in industry with those tools, is a different thing!

 

One general concept that did stick with me: as an engineer, it reminded of learning to fit curves through data points when in the Lab.

 

You could certainly create an "advanced fit" curves with many degrees, segments, etc... (high math!) that could go exactly through every data point (forget if that makes it "accurate" or "precise"? :-). But the curve was then very "bumpy".

 

Or you can use low-order math, and get a very smooth curve (even a line for very-low order!) that shows your data trend, but may not even pass through any of the actual points.

 

Probably does not help you in practice, but at least you are not alone if this stuff is not "obvious" :-)

 

Pat

Re: perplexing "Advanced Curve Fit"

Valued Contributor
Valued Contributor

Hi @PatMcManus. Very helpful suggestions in practice. Thank you!