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

So.... going back to his original question about the sweep, is there maybe an alternate method to achieve the desired result without using another program?

I think you need to create profile in each corner

Hi niko yeah currently without using any other program you need to get angled and scaled profiles into the corner junctures, then build sweeps between each of those.

A shortcut for getting the angled and scaled profiles is to make a polyline for the rail - if the rail is only made up of line segments then you can get a mitered corner sweep for it in MoI even if the whole rail is not on one plane.

So for example try sweeping the attached 3DM file in MoI - here I've drawn in a polyline for the rail instead of the original one that had slightly curved segments.

That produces a result like this directly in MoI:




If straight sections are ok then you are done there actually.

But if you want curvy sections, you will then want to extract the edges at the polyline miters by selecting them and doing Copy + Paste, and then do a sweep on each curved segment individually, between those profiles.

- Michael

Hi niko, here's an example of how to use that technique with a curved rail, this is how to build the second example I posted entirely in MoI.

I started by drawing a polyline snapping its points on to the rail like this:



Now sweep along the polyline, it will build a mitered result like this:



Select just the edges around the original juncture point, do a Ctrl+C and then Ctrl+V to duplicate the edges as regular curve objects, and then delete the segmented sweep, giving you this:




Now use the Transform > Orient command to copy the starting rectangle to the very end, or actually you could do it by duplicating those edges from the sweep as well:




Now it is ready to sweep, use Edit > Separate to break the rail into individual pieces, and do the sweep in sections, first one sweep here:



Then a second one here:




That's how I produced the attached 3DM file created only in MoI.

- Michael

Hi Michael,

>>That's how I produced the attached 3DM file created only in MoI.<<

I presume that result is just for fun, as it is a very bad output.
You will not produce a good result attempting a single angular bisector/trim at the 3d intersection

Hi Steve, sorry I don't have any idea what you are referring to - that's not a bad output at all, it's a full solid and seems to check out fine, no self intersections, etc...

Also I don't understand why you are talking about an angular trim - the sweeps in this case touch each other exactly because they come to a common angled profile.

That's the whole point of this method - to make a joined touching piece without using any trimming.

You have to use some method like this to make pieces join in this kind of situation because 2 regular shaped tubes will not really come together in a simple miter like that when the paths are all curving around in 3D space, that's what I've been describing in several previous posts in this thread with several examples.


Using an angled profile shape that is common to both sweeps, does make a result that touches, at the expense of it being a slightly slanted tube and not completely even thickness throughout.

If you think it is a bad result, you will need to explain what your complaint about it is - as far as I can tell it's all fine, for example here I have done a boolean in that area with a sphere and as you can see it gives a clean result:





- Michael

Hi Michael, just because a solid is produced does not make it correct lol.

Take a section of the solid to show profile.(which is far from correct)

Hi steve, actually that is totally correct for this case - the whole point of that result there is to generate pieces that touch each other at the sharp corner in the rail.

The purpose of that particular model is not to make a tube that has a uniform cross section.

Read back over some of the posts in this thread, I have some explanations in there.

Geometrically, you can either have a totally regular shaped tubes with even cross sections in them that do not come to a simple miter-like joint, _OR_ you can have a non-uniform tube that does come to a common simple joint which it does by making a somewhat slanted shift to the sweep.

Just because something has non-uniform thickness does not mean that it is not "correct" if it is solving some other problem that someone has put a higher priority on, like in this case coming to a common angled profile.


If you think it is possible to have both a regular shaped cross-section, _and_ at the same time have the pieces meet in a simple common miter-like joint, then please show an example.


- Michael

Also you could probably reduce (but not eliminate) the distortion by putting in a non-slanted profile like the starting one at some middle point or something like 3/4 point along the sweep so that it would hold more of a regular cross-section through more of its length and only start to shift closer towards the end.

But I think you've missed the point which is to make something that looks like a miter joint at the sharp juncture in the sweep path.

- Michael

I thought the point was to get the PROFILE swept around the curve with a mitered corner. There does need to be compromise but at what expense? Having such distortions in the profile IMHO is not good and I would follow more of a path of what NX(and other CAD) do by averaging the intersections.

This is a very(very) quick example that is more to what I would expect, although of course there is still compromise.

Hi Steve, well that approach of shifting control points just at the end as NX does produces bad geometry errors in other situations, see this previous post in the thread where I describe it in detail:

http://moi3d.com/forum/index.php?webtag=MOI&msg=3575.11

Is that kind of self-intersecting geometry what you would consider a proper result?

Not only that, but taking a section through the result you posted also shows distortion as well:




Right now it seems like that is not the best way to go, it seems to be a more risky approach with it making bad results on shorter pieces, although it does help with making the distortion located more at the end on longer pieces.


- Michael

Hi Michael,

>>Is that kind of self-intersecting geometry what you would consider a proper result?<<

I put forward a possible way to work, not that intersecting geometry produced from that are correct. You will have problems with this type of construction, but I still say that attempting such miter based on one intersecting bisector will not work well.

Here is that model I posted(before) again, but with the accuracy upped a little to attempt to produce a more straight profile.

- Steve

Thanks Michael

hi Pilou,

This models is composed mainly of boolean. It is very easy to make a curve, an extruded, and remove what is too much. Moi3d has very strong boolean I think. I use a lot of intermediate lines to produce the volumes, but it's surely the principle of this type of modeler. I have other modelers, however, it is very flexible and allows more creativity I think.
I'm french, I usually keep the interface in English, I make an exception this time ;-)

Temporary Curves:

@ ppj: L'interface française fait gagner 11 pixels de large sur l'espace de travail par rapport à l'anglaise! :D

French interface saves 11 pixels wide workspace compared to the English! :D
:)

Hi Steve,

> but I still say that attempting such miter based on one
> intersecting bisector will not work well.

I don't quite follow - it seems to be pretty clear that sweeping between angled profile curves does work better on the situation that was originally posted.

That's the one that was attached to the first post of this thread here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3575.1

That's actually a more simple situation than the one with the long curves.

I'd say that it is more important to generate a tolerable result (without any badly mangled or self-intersecting geometry) for the original case than focusing on generating a more uniform thickness result for the 2nd case which is more of an exaggerated test case.


I've attached the result of using this technique on the original posted model, it creates a result that has no self-intersecting areas, so it can be used for things like a boolean with the main hull.

The technique that you are saying is better makes for badly formed self-intersecting geometry here, which would likely cause boolean calculations to fail. I would have a hard time convincing people that is a better result than the attached version.

- Michael

Hi Michael,

>>I don't quite follow<<

That is obvious.

You are still working from a single bisector, although you can get a result of a solid, that does not make it correct. It may be OK for hobby stuff, but the model you posted, it would be rejected in my work, as there is error of between 0.025/0.05 in the position of the angled profile (I only bothered to check the first.)

As you now have it in your head, due to the bad geometry posted from the output of NX by another member, and you appear to believe that calculations can only be made from a single bisector, I will not waste my/your time further.


- Steve

Hi Steve, I'm sorry but you're not making very much sense here...


> It may be OK for hobby stuff,

Wow, you mean anybody else other than what you work on must be doing "hobby stuff" ? That's a quite patronizing attitude.

There are all kinds of people producing professional work that would like to simply get a good looking result for that case. Just because they want something quickly that looks good does not mean that they are doing "hobby stuff".


> but the model you posted, it would be rejected in my
> work, as there is error of between 0.025/0.05 in the
> position of the angled profile (I only bothered to check
> the first.)

So would the result posted from NX with the self intersecting geometry be accepted as a proper result for your work instead?

Or is there no CAD program that can automatically generate a result for that which you would consider acceptable? If so then MoI is no worse off than any other CAD program since none of them can do what you seem to want there.

You will probably need to do some custom modeling instead of using an automated tool to get what you consider to be correct.


> As you now have it in your head, due to the bad geometry
> posted from the output of NX by another member, and you
> appear to believe that calculations can only be made from a
> single bisector, I will not waste my/your time further.

Well, it's not just NX in particular, but rather that whole technique of morphing just the end control points of the sweep to the miter that is prone to that kind of self-overlapping error.

It's something that would be quite difficult to avoid with an automated algorithm without spending a really long time with heurstics or almost artificial intelligence type of analysis of the spacing and shaping, etc...


It's really curious that you say the method I used is not good, yet here is a simple case where it produces a result that the original poster would have most likely considered to be a great result...


- Michael