> > 3: re-parametrize surface or curve: any way for this MOI. Here I'm considering the method
> > in Softimage or Maya, where, "uniform re parametrization" acts similar to morphing of
> > uniformly distributed grid, with same UV point count, to another, curved surface.

> I think you mean a "rebuild" command that samples points on an existing surface and constructs a new one > through those sampled points? There is a rebuild command but it currently only works for curves, not for > surfaces:
> http://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

Well I meant something like in image. Selected one is exported as IGES from MOI, uniformly re - parametrized in Softimage, imported back into MOI. Points are on the same position, but shape is different, after Softimage re - parametrization. But it doesn't matter - exchange via IGES seems to works perfectly on MOI - Softimage route, so I can do this in Softimage.
I had to do some structure, where is really hard to define the volumes and blends between them, but also a lot of small details, impossible to do with Softimage's ancient NURBS tools- and it will take ages to with polygons. So it seems everything I want is available.

Please forget mu beginner's impression about 're- sampling everything'. Long time ago I've played a lot with Rhino beta, but everything I learned later belongs to DCC world, where keeping the point IDs seems to be more important than keeping the accurate shape.

Thank You kindly for your time, again.

Hi Anto,

> Well I meant something like in image. Selected one is exported as IGES from MOI,
> uniformly re - parametrized in Softimage, imported back into MOI. Points are on
> the same position, but shape is different, after Softimage re - parametrization. <...>

I see, so I guess what Softimage is doing in that case is throwing out what is called the "knot vector" part of the NURBS structure and instead creating what is called a "uniform knot vector" which basically means every control point has the same amount of influence on the spline shape.

But that's a sort of unusual thing to do with NURBS surfaces really, because as you mentioned it can cause the surface shape to mutate, sometimes in fairly odd lumpy bunched up ways if the original surface had a lot of non-uniform knot distribution...

Most of the time with NURBS surface modeling there is much more of an emphasis on preserving the shape of the curve or surface itself to some tolerance level rather than trying to preserve the particular position of the control points.

Maybe I could help you some more if I understood the particular reason _why_ you want to use this Softimage function on your surfaces to begin with... What is it that you're looking to gain by doing that?


The main focus for MoI for control point editing is to do that on curves, not really on surfaces. Once you have got some curves drawn and edited, then when you create surfaces from those curves it tries to make those generated surfaces be accurate to follow the overall shape of the curves. Some operations like intersections and sweeps work by an iterative refinement method where they add as many control points as needed to the generated curve in order to achieve a certain level of accuracy to the desired "ideal" shape. With that overall workflow, the specific arrangement of surface control points isn't really all that important, it's more about viewing the surface as a sheet of geometry that you know follows your profile curve shapes to a high level of accuracy.

And yes, this whole workflow is indeed quite different from the 3D point control-cage-focused type process that you'll be focused on with a polygon mesh modeler.

In a sub-d modeler, the process is kind of more like sculpting in a way, where you're doing a lot of squishing of points around on the 3D shape. MoI is designed with a pretty different workflow in mind from that, in MoI it's sort of more like illustration rather than sculpting, where you focus more on drawing 2D curves to define key profiles of the shapes, and then surfaces are generated directly from those profiles and not really squished around themselves directly in 3D.

The MoI workflow tends to work very well for man made objects that are often times well defined by 2D profile curves. By being able to do most of the work in 2D these kinds of shapes can be constructed very rapidly with MoI's main intended approach.

For shapes that are more lumpy organic type things, those are usually not very well defined by 2D profile curves and those type of shapes are usually better to do in a sub-d modeler instead of in MoI.

There is some limited amount of 3D surface control point squishing in MoI as well, but it's not really primarily designed to do things that way.

- Michael

Anto,

Point 1 and 2 would be my number 1 and 2 feature requests for MoI also, they would both be extremely useful features to have.

>Maybe I could help you some more if I understood the particular reason _why_ you want to use this Softimage function on your surfaces to begin with... What is it that you're looking to gain by doing that?

It's not only that. Actually I already have a small set of tools for attaching the NURBS grids to portions of mesh subd hull, mainly used for "unusual" purposes, like rigging, hair styling, emitting particles, so on. Something like "poor man T-Spline". From my understanding, if NURBS grid is attached to arbitrarily shaped, quad like mesh structure, it acts like "uniform". By the way, Maya has exactly the same function, with same name.
This time, as I have to stop with experiments. It's much easier to me, to attach these NURBS grids in Softimage, to existing mesh, then to export IGES to MOI for adding details - instead of finding curves on it. It's space ship model for use only in DCC app, accuracy doesn't matter. It's not what we consider as "organic".
Next time I hope I'll be able to do everything in MOI.

Hi Anto,

> From my understanding, if NURBS grid is attached to arbitrarily shaped, quad like mesh structure, it acts like "uniform".

I'm not sure if this is what you mean, but yes a totally regular quad mesh structure using sub-d modeling will behave the same as a uniform NURBS surface.

But I don't really understand why you wouldn't just use sub-d objects for these various things that you mention, like hair styling for example.

The main area where NURBS surfaces have benefits compared to sub-d meshes are when it comes to booleans and cutting operations. But you're probably not using stuff related to booleans when doing hair styling... ?

Just in general MoI itself is not focused on generating things for squiggly jiggly type stuff, it's more about building mechanical man-made objects (where booleans and 2D curve driven modeling is very useful) which are usually just animated with movement and rotation, not arbitrary squashing around.

- Michael

>But I don't really understand why you wouldn't just use sub-d objects for these various things that you mention, like hair styling for example.

NURBS surface provides always present UV space, perfect interpolation as well. Generally it's much easier, and faster, to use NURBS for any kind of defining the custom, deformable, 3d cord system.UV as XY, normal as Z, or like. Usually there's built - in constraint to NURBS surface, deforming operator that works in similar way to MOI flow, so on. Getting the same form SUBDs, takes more effort, means much slower computation time. For example, Softimage applies SUBD interpolation, always as last operator, after computation of collisions or distance queries - so it's more a display/ rendering feature, not something to use for interaction. But NURBS is taken fully interpolated, all the time.
There's traditional "Maya ribbon spine" rigging setup which utilizes NURBS surface: http://www.creativecrash.com/maya/tutorials/character/c/ribbon-spine-rig
Here is one small hair styling system created by me: http://area.autodesk.com/tutorials/mars_police_hair_and_render_breakdown. Here, polygons were used only as hulls for tweaking, only because Softimage has much better tool set for polygon tweaking.

Yes, almost all setups of this kind, utilizes single, open NURBS surface, or bunch of them. So built in tool set is more than enough.

Anyway, I bought MOI for modeling, as I noticed that with polygons, about half of modeling time (or much more) goes onto preparing the geometry for adding the details.

There is also individual approach, how someone visualizes the forms. Having a zero experience with CAD modeling, I'd visualize, for example, bottle as modified cylinder, house as bunch of boxes. Not as revolution along axis or extruded plan. But that's just me :).