Also the profile too big for the path

@Danny,

Can you please try this case in NX ?

Hi Michael,

Many thanks for your help ; I really appreciate you took the time to answer my question . I have understood you explanation. I think I will blend the Extrude/Bloolean/Scale functions. I am really statisfied by the boolean function. I will let you know if I get any results.


Thanks,

Philippe

Hi Anis,

> Can you please try this case in NX ?

NX handles this OK but we're talking about two different geometry engines here, NX is using the more mature, robust and expensive parasolid kernel.
I think Michaels comparison there with 'like' programs is a better comparison, apples with apples, if your trying to compare with NX it's like comparing apples with an apple juicer.

Cheers

Hi Danny, actually although the NX generated one looks great at a first glance it actually has some problems in it.

It seems to be constructed with a different technique of kind of sliding out the control points for the ends of sweep segments.

But that technique has produced some areas where the control points have been slid backwards so that the created surface is a badly formed self-intersecting one.


Here's a zoom in to one problem area:









Note that the surface in that spot has a sudden abrupt 180 degree hook in it:




If you turn on surface control points you can see what has happened, there were several straight sections coming up to the miter, and then it produced the miter by shifting control points around, but that caused the end of the surface to come partly back over one of the previous straight sections:




The other short segment has the same kind of problem.

That particular technique that is being used there works pretty good if the sweep path is not very tightly bent in that zone near the miter (because tightly bent ones will have numerous control points all over it), and if the miter angles are smaller so that they don't shift the points back over a previous section so much.


There is another possible technique which is to kind of place in slanted profile curves at the corners of each miter spot and use those as profiles for the sweep. Rhino actually seems to have a somewhat new option for that called "untrimmed miters" which works pretty good for this case but does not work well for more bendy paths.

That would probably be a good option to have in Sweep in MoI too though. But that kind of produces a different kind of problem where creating a surface between angled profiles makes for some variation in the "tube thickness" because the sweep profile has a kind of angular turn to it as it moves along the path, similar to the example in this previous post:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3546.6


So anyway as you can see it is not really an easy problem to solve, even NX / Parasolid did not get it right... and I think that may be due to it actually being a geometric impossibility to have exact constant tube thickness and also exactly meeting miters on non-planar curved segments like this.

- Michael

Thank you very much, very impressive NX. I thought exactly this :-)

Philippe.

Well done Michael.

Export is deformed following the default. Clearly.

Hi ppj, for rendering purposes that will probably be ok though since the messy area is small in size and also kind of internal to the overall shape.

But that kind of self-intersecting surface will cause problems in many other kinds of operations, things like booleans will have problems operating in those areas because the intersection calculation between something like that is not very well defined. So from a kind of "NURBS solid model integrity" standpoint it is not good to have results like that.


Probably in v3 I will be able to experiment with an alternate mitering technique of basically taking the profile curve and rotating and stretching it and placing it at the corner areas, which should give a non-intersecting result usually but will probably not be 100% even tube thickness since it will make a kind of slanting effect.


- Michael

Hi Danny, it would be interesting if you could try the attached sweep example in NX and see what it does to it.

This one has a higher degree of non-planarity and bendy-ness to it, it should show how swoopy things are not really guaranteed to actually meet at a common normal miter.

I wonder if they will do something like twist the surfaces at the very end to force them to align or what...





- Michael

Hi Michael,

I knew you'd jump on this as soon as I posted it :) I was on my way out and was waiting for the wife to put on her finishing touches and didn't have time to analyse the sweep, I was going to try the tuber_miter as well but the wife had finished and we had to go :(

So I'm back now and posted the NX version of tuber_miter, and again no time to analyse it, but I'm sure you'll tear it apart Michael ;)

Cheers

Hi Danny, thanks for giving that one a try!

It's an interesting result - it looks like it is forcing the miter join by warping the ends of the sweep, I guess maybe in the same kind of tweaking of the control points at the end, although maybe it is a bit different than the other one.

That produces a kind of miter-join result but at the expense of not having fully regular thickness tube, just by eyeballing it you can see the thickness is different in these areas for example:





Here you can see why there is not a constant thickness - here I've set up a bunch of isoparm curves on one of the other surfaces and as you can see the warping at the end causes a kind of slanting to the cross-sections in the generated surface, they are not perpendicular to the central rail anymore:




However, that does not seem to really be a particularly bad result, because I'm pretty sure that it is a physical impossibility to maintain constant thickness in this situation and also have a nice matching miter, you can have either one or the other. And if you have bothered to have a single joined rail curve with a kink in it, I guess that probably means you are actually more interested in the miter.


- Michael

One thing I'm not quite sure what to make of with that NX result is that the shape at the miter here:



Has actually had a kind of shearing happen on it, if you lay that flat down on a plane it looks like this:




I guess it's actually a stretch of the profile which is something that goes along with a miter corner, but I'm not sure why it stretched in that particular direction.

- Michael

Hi Danny,

I am aware about the geometry kernel.
I want to know the result in NX, is NX capable or not ?

Thanks Danny :)

Hi Michael and Danny.....

I tried this case in SWX ( use the same kernel as NX ).
For case #1 = SWX cant produce any result. I dont know, it is the software or I dont understand the correct technique to get the result.
For case #2 = see attached

Hope this will give you more data to examine.

Thanks

Hi Anis,

> I want to know the result in NX, is NX capable or not ?

I've attached the results in the above posts, Michael explains his findings when examining the results from NX.

-

Seen your model on the Gallery, astonished result!
http://moi3d.com/gallery/viewitem.php?id=298
and seen you use the French UI ;)
Have you some remarks about it?

Hi Anis, well there's certainly no doubt that NX is a very capable program!

Of course with geometry there is such an infinite variety of cases that there will always be cases where some different kind of an approach is better suited for a particular situation.

That's why it is can be nice to have several programs in your toolbox when possible, because there just does not exist a single program that is always without question the absolute best in every single possible kind of geometric circumstance.


One nice thing about NX's result even in the one that it had a problem, is that it actually generated a result that can then be fixed up without much extra work by just deleting the short sections that have the problem and putting in something like Lofts in those areas.

It's not really that great when something just totally fails to generate any result like what you mentioned SolidWorks did for this particular case. That might be due to something in SolidWorks that detects that "bad geometry" was created and so therefore fails the whole operation. That kind of thing has sort of been a problem in parametric solid modelers since very early on in their existence.

- Michael

Hi Anis, also you wrote:

> I tried this case in SWX ( use the same kernel as NX ).
> <....>
> For case #2 = see attached

It's interesting that it is such a different result - it must be using some other variation of sweep or different settings or something like despite having the same kernel.

This result is really pretty bad with such bad wiggles and twisting in the shape, and it actually also has a kind of severe folding back on itself type problem right at the miter location as well.

- Michael

So the key is not only engine of the software.
But also who develop the software use the engine, right ?

Thanks Michael for your valuable info....

Hi Anis,

> So the key is not only engine of the software.
> But also who develop the software use the engine, right ?

Yup, that's definitely true.

MoI is an example of that as well, I re-wrote a large amount (like maybe 60% or so of the total or maybe even more) of the sweep code for MoI's sweep function from the stock one in the geometry library because it had various restrictions that I didn't want to have (stuff like profiles must touch the rail curve, etc...).

But the custom code that I wrote still uses a lot of functions from the geometry library for various low level calculations as well, so the custom code still depends on the library in a lot of ways.

You may find that same kind of situation in other programs as well, where some programs may have developed some functions differently from one another despite having the same base geometry library.

- Michael