I just knocked together a very quick and dirty tutorial for getting a face from a poly modeling or polysculpting software to MOI NURBS model. Sorry that it turned out a bit ugly. Only have GIMP installed on this machine so it was a monumental struggle to lay this out. =P

This is more or less how my head started, even though I completely resurfaced it a couple of times with new curves.

This could actually be semi-automated in the obj23dmwireframe tool if it automatically deleted any edge more vertical than say 45 degrees to the horizontal and just left the horizontal edges useful for curve creation. A choice of horizontal or vertical lines wouldn't be bad either.

Hope some of you find this useful, even though it is annoyingly manual.

>> Another method that I see sometimes used is a kind of hybrid NURBS / Polygon approach where different individual pieces are modeled using NURBS tools like a sweep for a top cheekbone, or most of a nose, but you keep all the pieces separated with some space between them and then in the poly modeler add polygons to connect the pieces together.<<

Dassault Systemes seem to be using a subD/NURBs hybrid modeler in their Imagine and Shape product

http://www.youtube.com/watch?v=RwOuaNvpPLI

It looks like a subD control cage being used to a drive a NURBS engine.


I would personally love to see a voxel based freeform foam/gel modeler driving a NURBS surface engine or some kind of metaballs -> NURBS modeler for organic stuff. One can dream, heh heh. =]

Hi curveman,

> It looks like a subD control cage being used to a drive a NURBS engine.

Yup, it's pretty interesting! And only something like $10,000 to buy...

From what I can tell, the modeler itself is all sub-d and then the interesting part is that it has the ability to convert the Subd surface into a set of stitched together NURBS surfaces that can then be imported into their regular NURBS CAD tools.

There is actually a pretty close relationship between the Catmull-clark type subdivision surfaces and NURBS - in fact when you have a very regular quad layout (with each mesh vertex having 4 edges coming out from it), there is a really easy direct conversion possible between Catmull-clark subd and NURBS.

It gets much trickier where there is a non-quad layout. In those areas there isn't an exact conversion and instead something has to be done that calculates a kind of fitted NURBS approximation in there.

Maya actually has some similar conversion tools built in, although they don't seem to have gotten much development for quite a while, and T-splines on Rhino is the other recent thing that is pursuing this kind of Subd + NURBS hybrid approach.

In the future I think this kind of combination will get to be more common.


> I would personally love to see a voxel based freeform foam/gel modeler driving
> a NURBS surface engine or some kind of metaballs -> NURBS modeler for
> organic stuff. One can dream, heh heh. =]

That's a lot more difficult because at least with Sub-d there are a lot of areas that have the exact conversion.

With these other types, there is no exact conversion anywhere, so the entire thing has to go through a kind of fitting / optimization type process.

There are some types of "reverse engineering" type tools that are set up to do this kind of processing, for example check out geomagic.

- Michael

Hi Curveman - It's very interesting and thanks for the quick guide.

I'm a rhino user so I think I can approach to MoI a bit easier than other tools. Even the functions in MoI are not so many as Rhino but I think that some of functions in MoI are stronger than the Rhino or other tools.

I couldn't withstand temtation of MoI and I'm enjoying it. :-)


Thanks,
momso

Hi Momso, I'm glad you're enjoying MoI!

One quick note - it is easy to use MoI and Rhino in combination with one another, you can share data back and forth using Copy and Paste between them, you don't even need to save to a file.

- Michael

Michael,

Thanks for the tip. I didn't know about it, so I was save as .3dm file and open it in Rhino again. It's cool for using copy and paste in between MoI and Rhino.
As you said, even official release is not so different from the current beta version, but I'm waiting for coming it out .

/momso

>> That's a lot more difficult because at least with Sub-d there are a lot of areas that have the exact conversion.

>> With these other types, there is no exact conversion anywhere, so the entire thing has to go through a kind of fitting / optimization type process.

There's all sorts of clever ways to go from unstructured stuff like voxels to NURBS without necessarily getting into super complex fitting algorithms. Here's one "cheap and dirty" =) way I can think of doing it.
This method would run into problems when a model has a hole or cavity that goes from one side all the way through to the other, or with something like a tree where things branch off from the main trunk and need to be handled separately. But even that could be fixed with a bit of clever coding I think and the user himself could be tasked with segmenting or color coding the voxel volume so that it can be parsed easily by the NURBS conversion algorithm.

I think this is one potential method for creating a bridge between truly 3D freeform sculpting that feels like shaping things with a soft modeling foam or gel, and more structured NURBs modeling. It would be enough if you could rough out a 3D organic shape quickly with a voxel brush/nozzle and get an "OK" quality NURBs model or set of curves out of it that can serve as a guide for the construction of a cleaner, better defined NURBS model.

I suppose another way to go about fast organic modeling is to subD model the object, export the subD control cage to OBJ, 3DM it and the retrace the cage with spline loops in MOI.

Here's a somewhat sloppy first attempt at working off a subD cage. It actually seems like a decent way to block out an organic shape and could definitely be done better than I've done did here.