Nurbs?

[Per-Anders]

to be honest with the ammount of work involved it would be of most use for those importing from other apps, as in cinema would need a good solid Nurbs library. nurbs tools would require a massive ammount of work on top of that, and i don't think maxon woudl want to do that unless they could be the best possible, which just isn't really feasible with competitoni from the likes of rhino and studio tools. but i think it's feasible to have the nurbs functionality itself (even though that would be a lot of work in itself) without much in way of tools, for instance in the way that xsi has it. this allows you to use a dedicated Nurbs modeler specific for the job and at least import the model into cinema without ending up with a mess.

[R1PPER]

I read over at the modeling forum that Nurbs are not as used now as everyone uses Sub-d. As im fairly new to this game...what do they mean. Am i wasting my time learning to nurbs model? What is a basic definition of Sub-d???

[Byla]

if you are using hypernurbs, that means, you are using Sub Ds actually. So, dont worry.

[malc0lm]

So, what exactly is NURBS modeling? And how does it differ from SubD?

Cheers

[mnu]

Hi malc0lm,

I try to explain it in english but please don't blame me for typos, as this stuff is kind of complicated:-)

Seen form the renderers point of view theres no difference between SDS and Nurbs. Both have to be converted to polygons to be renderd. The difference between Nurbs (Non uniform rational B-Splines) and Subdivision Surfaces is a mathematical one. Both define a surface in 3D space through math. This mathematically defined surface is then converted to polygons in a process called "tesselating". These tesselated polygonal models are a kind of approximation of the mathematically defined surface, and they are the ones that actually will be rendered. The subdivision surface uses an algorithm to refine a rough polygonal surface. This algorithm works similar to the smoothing algorithm found in standard C4D BSplines. It computes intermediate points, between "real" points, and smoothes these out. If one iterates this smoothing process over and over again, until infinity, a smooth surface (maybe you can call it boundary surface) is the result. Nurbs on the other hand take another aproach. Here you first use Nurbs Curves to define two dimensional patches. These patches, that are exactly defined through math are parametrized (is this spelled correctly?) in local uv space. By attaching, stiching and merging those patches you can build a complex model that is exactly parametrically defined, too.

Because of these differences in the underlying math SDS and Nurbs both have advantages and disadvantages. With SDS you can build a model of arbitary topology as one single surface. This is well suited for animation as you never risk to destroy the model by deforming it. Unfortunately SDS aren't that exact. For example you cannot describe a perfect circle with SDS. Here lies the strength of Nurbs. Because of their parametrical nature you are able to model very exactly. You have control over every aspect of the surface. This is very good for product design, where you need exact models but seldomly animate them. Because of Nurbs consisting of several aligned surfaces animation can become tricky as you have to maintain the topology while deforming the mesh.

So the lack of so called "real" Nurbs is not a vital problem to C4D as you can build nearly everything with SDS, too. Nevertheless, importing and rendering Nurbs directly in C4D would be a very nice thing, as mdme_sadie mentioned, as this ability would make product visualization and architectual stuff much easier.

cheers mnu

[malc0lm]

Thank you very much for clearing that up and taking time to do so!

Cheers!

[mikeh64]

thanks for the description - it does seem like real nurbs aren't that important to C4D.

If a model is created in a real nurbs modeler - what is the best way currently to get it into C4D? Can real nurbs be converted into polygons for export?

I'm assuming most nurbs modelers have some sort of "convert" function, or a exportable format that is more successful to move to C4D:

- what should I tell a person sending me a "nurbs created" model as far as export and file format?
- are there "little things" in their export or convert function dialog boxes that help a model move to Cinema successfully?

[mnu]

Hi mikeh64,

Yes, you can export the tesselated version of a Nurbs model to C4D. This involves tesselating it by hand first, because automatic tesselation doesn't produce satisfying results in most of the cases. This is because every Nurbs patch is tesselated individually. So, polys won't mach where the individual Nurbs patches met previously. While this is no problem for a program that supports real Nurbs it is a big one for programs like cinema. The idea of Nurbs is, to tesselate them very fine. So that a polygon of the tesselated version is as small a a pixel in the rendered image. Than, polys that don't align aren't a problem anymore. If tesselating for export it is a totally different story as we cannot tesselate that fine. So a lot of cleaning up and hand work is involved to produce a polygon model that is usable.

cheers mnu

[AdamT]

If possible it's best to get an .obj file since (other than FBX) this is the only format that will come in woth normals data. You can get some hard-to-remove artifacts without the normals info.

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