blimey,

thanks Steve

Hi Steve, so the big step that you're kind of missing here is that when you project a curve onto a surface, you often don't want to get rid of the surface and try to recreate it from scratch, instead you want to actually make use of the surface itself too, like for instance by trimming the surface by that curve.

Trying to recreate the surface that goes through a non-planar projected curve is going to be really difficult - but you don't need to recreate it, because you've already got it there since it was what you projected on to in the first place. You just need to cut it using the Trim command.

But also another thing is that several commands like both booleans and trim already have curve projection built into them so you don't need to do them as a separate manual step like it looks like you've done here.

It looks like the final result that you want is an extrusion with rounded ends.

A good way to create that is actually by a totally different process than projecting curves and then trying to create surfaces to fill them in, you can instead build an extrusion and then cut the extrusion to produce the rounded ends.

So in your case here, you'd start with 2 planar curves like this:



Extrude those out to make your base shape:



Now position some spheres to use for cutting it up:




Select all 3 objects, and then use the Construct > Boolean > Merge command, that will slice up all the objects and leave all the results behind, then you just delete the parts that you don't want to keep. After you delete the pieces of the sphere you'll see your extrusion was sliced up like this:



So then delete the outer pieces and only keep this inside one which has the shape you want:




Usually this kind of process of building an extended solid base shape and then cutting it up is the best way to approach things rather than trying to build individual projected curves and then trying to fill those in.


You want to kind of take a look at your object and try to think if it has some kind of central underlying element to it which is then cut off at a certain spot. In your case it's exactly that - you want to have a base shape that is an extrusion but that then has cut off rounded ends. So usually with NURBS modeling you want to actually build in that exact method, build the extrusion and then cut it as shown above.

- Michael

So like you guys are mentioning above you can also build this shape by building just a starting surface and then extruding it - if you extrude a surface you will always get caps on it since it can be capped just by copying the potentially non-planar surface to the other side.

But I would encourage you to think more along the lines of slicing a base solid like I showed above, because it's a lot more general purpose and you will generally use that same process to take other kinds of cuts out of the object as well like slicing it by side profiles.

If you did want to do it by extruding a surface you don't need to use curve projection as a separate step because Trim already has projection built into it, so just trim the sphere directly with your 2D profiles, then extrude the trimmed sphere surface piece.

- Michael

Hi Stever - also see some of these previous threads for some other discussion about modeling with solids and cutting up extended shapes.

This is basically a key difference between the NURBS modeling process and the polygon modeling process - with NURBS modeling booleans and cutting operations are a primary way of doing things and often times that will mean making an initial simple extended piece and then cutting it up rather than trying to sort of draw a net of 3D curves and then trying to fill them in, which is also possible but better reserved for more special situations.

Anyway, some other discussion on this here:

http://moi3d.com/forum/index.php?webtag=MOI&msg=4640.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=3795.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=4298.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=4163.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=2282.2

Some of those threads may help to give you more of the idea of the different modeling mindset (as compared to polygon modeling) that you generally want to approach things with in MoI.

- Michael

Hi michael,

Much appreciate the explanation, learning a lot.

Can give me a scenario when you would best use curves/isect

Hi Steve, since Trim and booleans actually have curve projection or extrusion built in, you usually would use curve projection only for intermediate construction steps, like for instance see here for an example where curves are projected on to a sphere and then used as the paths for building sweeps:
http://moi3d.com/forum/index.php?webtag=MOI&msg=817.8

Working with individual surfaces where you would trim individual surfaces instead of solids tends to be a somewhat more advanced kind of toolset, it can sometimes be helpful to work at a surface level if you want to kind of disassemble and rework some particular area of an existing solid though. There is an object repair tutorial here that shows that kind of use in a lot more detail:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

But as far as building basic models goes, I would encourage you to focus more on using solids for doing basic shapes since for general stuff it tends to be more convenient and quick to use the solid toolset.

- Michael

Hi Steve, also one other note:

> Can give me a scenario when you would best use curves/isect

You still do use curves when working with solids as well, like for example in the solids workflow that I showed above there are still curves involved as the first step in creating the base extrusion shape.

The difference though is that you can make stuff happen working more with 2D curves only rather than trying to work with curves that are warping around all over the place in 3D.

Of course, it also all depends on what kind of work you're doing and what particular kinds of models you're creating - if your models are made up of more stylized swoopy surfaces that don't resemble extrusions or revolutions very much then you'll proably be working more with 3D swoopy curves to construct such stuff.

If your models look more like they incorporate some more 2D profile elements in them like they have the base shape of an extrusion, then those are the kinds of things that tend to happen more quickly and easily by working with 2D curves and solids rather than working with 3D swoopy curves.

This is all just kind of general advice though - which particular tools will work best can depend on what particular kind of shape you're trying to build.

The kinds of shapes that are well suited for using 2D curves though tend to be the ones that you can really get built very quickly using more solids + booleans methods though.

- Michael

Great stuff, thanks Michael

Yeah cool solution indeed yhanks for that Michael.
I need to change the way how I think something must/can be modeled. I still think to much in a polygon way. :-)

Peace,
Rich_Art. ;-)

"...I still think to much in a polygon way. :-)"

I think that's half my problem as well :-)

Steve

LoL.. Nice to hear I'm not the only die hard polygon modeler. :-)

Peace,
Rich_Art. ;-)

Hi Stever & Rich_Art - that's a pretty common thing to have some difficulty thinking differently than a polygon modeling strategy. I mean it's really to be expected if you've spent a long time thinking about modeling things in that particular way.

For NURBS modeling the basic idea is to think more about cutting parts with booleans as a primary way of making the shape.

It can be easier to recognize to use a boolean when you are cutting a hole out of the interior of an object, that just kind of registers in the mind more easily as a "cut".

The part that seems to be harder for polygon modelers (and just maybe in general too) to often see is applying booleans that cut some of the outside part of the object away instead of only cutting away interior holes.

Anyway, that seems to come up fairly often so that general idea of building some extended shape and then cutting off some pieces of it is just something to try and keep in mind when you're deciding how to approach a particular shape. If it looks like there is some kind of underlying broad shape that then comes to some sudden end or has some kind of irregularity in its borders, you'll usually want to model that big underlying shape first and then apply cuts to that.


Once you get the knack of this method though it becomes very quick to construct mechanical shapes which often fit in really well with that technique.

- Michael

Thanks Michael. I just need to use Moi3D more for modeling and when I do this, modeling with Moi3D will become a 2nd nature like C4D polygon modeling is for me now.

Peace,
Rich_Art. ;-)

Cheers

For me learning poly modelling in going to be a very long process (learning curve) for me. I'm competent in C4D and at simple poly models but get frustrated when wanting do something more complex.

But I tend to want to model mechanical hard surface objects anyway, so Moi seems to be more logical way of modelling now and faster.

I have to be honest for me I enjoy modelling more with my trial version of MoI than I do modelling in C4D, but yes I know each has their own purpose.

I just wondering if its poly modelling in general I don't get on with or if its C4D. Wonder if the poly modelling experience in Modo is different?

Steve

Hi Steve,

> I just wondering if its poly modelling in general I
> don't get on with or if its C4D. Wonder if the poly
> modelling experience in Modo is different?

It's hard to say for sure but I wouldn't be too surprised if it's poly modeling in general that you don't like - just in general polygon modeling tends to be not well suited for mechanical type shape modeling. Poly modeling is much more about manipulating a cage of points, basically working in 3D all the time and not really focused on using 2D profile curves.

The poly modeling toolset is really effective for doing sculpted organic shapes, characters, faces, animals, stuff like that. But it's also kind of a generally higher learning curve, it needs more experience and sort of needs developing higher level of 3d spatial awareness. It can take quite a bit of time to develop the skills it requires.


Modo though is a lot more primarily focused on modeling than C4D, and it's not unusual for people using C4D to also use Modo as a modeling tool, so if you do want to do polygon modeling it can be worth checking out. Also if you want to pursue poly modeling there is a streamlined modeler called Silo that is also worth looking into: http://www.nevercenter.com/silo/


For mechanical shapes though you'll usually find those are really well suited for MoI's NURBS toolset.


- Michael