One thing that I've noticed is that people coming from a poly modeling background have difficulty with thinking of trimming and cutting operations as a "first class" primary way to do modeling.

I'm sure that's because booleans just don't work very well in poly modeling and they're usually something that people have learned to completely avoid, and instead to construct all pieces of the model by edgeflow lines.

That's probably the biggest difference between poly modeling and NURBS modeling - in NURBS modeling trimming/cutting/boolean operations are usually actually the best way to get things done, so it actually is better to try to figure out if you are able to use them as the first plan of action rather than trying to avoid it.

You can use the freeform surface creation tools as well, but you generally want to use them to form large extended surface sheets and you usually should not try to directly surface all the final edges of your end model - instead many of those final edges should come from intersections and cutting operations, particularly things that have a 2D profile to them.

Once you get the hang of this, things can go very quickly though, because it is actually much quicker to build things in this way since drawing and managing 2D curves is easier than managing full 3D swooping stuff.

Not every kind of model is applicable to this kind of workflow - if your shape does not have any kind of 2D profiles to it then you'll need to use a more full 3D workflow, but even then you'll still want to try to build simple extended surfaces and you can cut those surfaces with other 3D surfaces rather than curves, it's just easier when you are able to use curves directly.

If your model does not really contain any kind of shape in it that you can identify as the full underlying form that is then cut, then that's the kind of model that's better done with poly modeling tools instead - think of stuff like an ear or a nose or something like that - those work better with poly modeling tools.


But for mechanical or man-made shapes that often manufactured by having pieces cut out of some larger initial stock, the NURBS workflow can produce that stuff really quickly (and also more accurately) than poly modeling, but you basically need to approach it in almost the same kind of way that it's actually built - try to think about making "pieces of stock" like a big sheet or a block that will then have some areas removed to make the final shape.


- Michael

Also a couple more previous discussions on why you usually want to make the top and bottom surfaces like that as extrusions and not with a pinched-together surface:

These have some more illustrations and explanation:

http://moi3d.com/forum/index.php?webtag=MOI&msg=4344.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=3956.1


You can make a pinched-together self-intersecting "bad" surface if the only thing you want to do with it after that is just look at it or export it to a rendering program.

But if you want to do more modeling operations on it, particularly ones that involve surface/surface intersection like booleans or filleting, then you'll run into a lot of problems.


Just being pinched together itself is not really the problem - it's how things are shaped in the neighborhood of the pinching. It can be possible to create an ok surface that way as long as you're very careful about how the curves are shaped in the area where they touch, they should be exactly symmetrical and have a shared tangent and especially don't have any inward curving shape like this:




Even the slightest bit of something with that kind of shape will make a bad surface that folds over itself in that tip region. It's so easy for that to happen that it's really best to plan to make such things as trimmed extrusions from the beginning though.

- Michael

"... for mechanical or man-made shapes that often manufactured by having pieces cut out of some larger initial stock, the NURBS workflow can produce that stuff really quickly"

Yep - that's how I got my head wrapped around the NURBs method (fortunately MoI was my first & only modeling tool, so I didn't have to un-learn anything.

My background is as a machinist. So I look at modeling exactly as Michael describes. If I want to make something in the shop, I pick a solid chunk of metal that is closest to my final result: Round bar stock for something made on the lathe, a solid block for something made on the mill. CNC tool paths on the machine correspond to trimming with curves in MoI for getting to the basic shape. From that basic foundation you have many other tools available.

Kind of like when I used to carve a bar of soap as a kid (before video games were invented :) Want to carve a rocket ship? Just cut away everything that doesn't look like a rocket ship :)

Ed

Hello There,

first, thanks a lott!!! amazing what amound of help and good advice I get here in so short time. so, thanks a lot for that.

As you guys expected I come from poly and simple nurbs modeling. that kind of stuff that you find in most major 3D animation packages. never the less I thought I realised the main differences and the advantages of nurbsmodelling (good boolean for example). but there are quite some things that I miss interpreted. I for example thought that if you use one and the same spline for 2 surfaces that they would match together.

But as I understand your advice. never handle with something different than closed shapes. and use trims and booleans with it. doublecheck if the result is a closed shape again.

Is there a way to check whether something is a closed shape?

and the secons thing I learned: If you ever have a batch of single surfaces that you want to connect. try it in different scales. by the way to be able to define a treshhold and get a realtime feetback (color) which shapes conected would be great i think.

so... thanks a lot for your advice.. I now go on and will try to adopt it.

best regards
Jops

There is a script you can assign to a hot key that shows open edges on a joined surface. I use this but I can't remember where I got it from.

Hi Steve,

> There is a script you can assign to a hot key that shows open
> edges on a joined surface. I use this but I can't remember
> where I got it from.

Yeah, that's particularly useful - you probably got it from Petr's page here:
http://kyticka.webzdarma.cz/3d/moi/#SelectNaked

The script is:

script: /* Show naked edges */ var gd = moi.geometryDatabase; gd.deselectAll(); var breps = gd.getObjects().getBreps(); for ( var i = 0; i < breps.length; ++i ) breps.item(i).getNakedEdges().setProperty( 'selected', true );


You paste that in to the "Command" part of a new shortcut key - I've got it hooked up to my N key so I can push N to show the naked edges.

- Michael

Hi Jops,

> but there are quite some things that I miss interpreted.
> I for example thought that if you use one and the same
> spline for 2 surfaces that they would match together.

Well, that actually should be the case - or at least the stuff generated from the same curves is supposed to be close enough to be joinable.

But some kinds of surface creation methods involve some kind of refinement of the generated surface until it hits a certain level of accuracy - in MoI v1 and v2 the Network command uses a somewhat looser tolerance than the other commands (because in some situations with a lot of generator curves it can make a really pretty dense surface), so it was possible for things built by Network off of the same curves to be just slightly out of Join tolerance.

That's fixed in the current v3 betas, but for v2 a workaround is to scale the objects down by 1/10 in size and then do the join.

So it is basically a bug in Network that's been fixed in v3.

You were not wrong with that idea really - and pretty much any other command other than Network should behave the way that you were expecting.

Right now I have not really focused so much on the workflow of building your entire model out of a whole lot of side-by-side networks, because that's kind of more advanced workflow and doesn't really leverage the greatest convenience factor of leveraging 2D curves and solids which is really where NURBS modeling has its greatest strengths.

If you want to build a shape entirely through a whole ton of Network surfaces, it can be kind of a sign that the model may have been better off build in polygons anyway - it can be difficult to get something built in a patchwork way like that to be all smooth, while polygon sub-d modeling has a nice way of smoothing and melting down a patchwork of connected polygons.


> But as I understand your advice. never handle with something
> different than closed shapes. and use trims and booleans with it.
> doublecheck if the result is a closed shape again.

Yup, that's the idea - you certainly can temporarily break things into individual surfaces for particular situations, but if you're only drawing 100% 3D swoopy curves and never doing any trims or booleans on solids, it's probably a sign that you're not really using the boolean and 2D curve toolset to its best advantage.


> Is there a way to check whether something is a closed shape?

When you select the shape, look at the object type indicator inside the object properties panel in the upper-right area of the main window. It's to the right of the object name. If that reads "solid" then it means you have a closed shape. If that says just "surface" or "joined surface" that means you have a non-solid (either just one surface or several surfaces joined together but not fully closed off).

If you do not have a solid then you can use the script in the message above in this thread to highlight the edges which are not joined between 2 surfaces, that will show you where the openings are.


> and the secons thing I learned: If you ever have a batch of
> single surfaces that you want to connect. try it in different scales.

Yup, although that's basically a workaround, but it will work. That's because when you scale objects down the gaps between the surfaces also shrink along with the whole object scale, and once 2 surface edges are within 0.005 units of one another that will allow them to be joined.

- Michael

Many thanks for all that help guys!
I´ll dig into that on the weekend since right now I´m at work...

thanks for that... nice comunity here :)

I think I get there...

getting better all the time.

i guess i will purchase MOI

is there a hint when V3 will come, and will there be a grace periot?

Thanks a lott
Jops

Hi Jops,

> is there a hint when V3 will come, and will there be a grace periot?

The V3 final release is a ways out, maybe something like a year away from now. I'm not sure about the grace period, I guess there will probably be one.

- Michael