[NURBS] Why don't we talk about tools? : )

The interface, modeling, 3d editing tools, import/export, feature requests, etc

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Joined: Mon Oct 14, 2002 8:43 am

Postby Noiprox » Thu Nov 14, 2002 4:50 am

The models in the Final Fantasy movie and Pixar's movies are NURBS. Yeah.

In general, Blender's modelling capabilities are rudimentary and in dire need of programmer attention. Both subdivision surfaces and NURBS are absolutely essential tools in any modern high-end 3D package, such as Blender aspires to be.

Dani, the problems you claim subsurfs have are problems with Blender's crude implementation. Research on subdivision surfaces has been going on for decades. Blender implements the algorithm described in the classic paper by Catmull and Clark years ago. It has since been proven that it is quite possible to evaluate subsurfs at arbitrary points directly. For those who don't understand, that means it is possible to raytrace (or render with some other algorithm such as scanline or REYES) subsurfs directly without subdividing the control mesh, so it does not necessarily require excessive amounts of memory.
The CatClark algorithm does not handle triangles the way you might expect them to because a triangle does not provide enough information to build proper quadrilaterals with. Just learn how to use the tool, instead of complaining about a property you don't understand.
Subdivision surfaces can also be subdivided adaptively, which is another important point to consider since that can dramatically reduce memory requirements while still providing an excellent final mesh. The adaptive tesselating algorithms are so efficient, they might even be useful in realtime. That is, for visualizing the surface for you while you are modelling.
There are many approaches to texturing subdivision surfaces. It's not awfully difficult to unwrap a subsurf mesh for UV texturing. If you are too lazy and would prefer it to be served on a silver platter as it (sometimes) is with NURBS, I have even seen algorithms that try to unwrap complex meshes automatically. Blender's shaders ("materials") and texturing are another part of Blender that need a lot of work.
CSG and SubSurfs are certainly not designed to work together, and if you absolutely must do CSG with a SubSurf model, it is best to convert it to a high-poly mesh first.

Now on to NURBS. NURBS is a mathematically stable and mature system, which makes it suitable for CAD and any modelling task where precision is important. Modelling a computer mouse is an excellent example of where NURBS would be better suited to the task than SubSurfs. Modelling a car is another (typical) example. NURBS is also readily paramterized since they are parametric curves (a truism..), making them comparatively easy to apply textures to. There are also robust algorithms for adaptive tesselation of NURBS, and direct evaluation is possible (simply by using the equations that formally define NURBS curves or surfaces), so that they can also be rendered pixel-perfect with relatively little complication (actually, numerical instability can play a role in some cases...a complication..).

So, in summary and conclusion, my thesis is that both tools are essential and that Blender is sorely lacking in both. Therefore, I think both should be high on the priority list for Blender's future developments.

Dieter Buys

Posts: 251
Joined: Fri Oct 18, 2002 8:35 pm

Postby Dani » Fri Nov 15, 2002 9:11 pm

Yeah, yeah, I'm a lazy guy, and i'm never happy with what I have...

I mean, I think i've been doing enough caracter modelling to understand how blender's subsurfaces work. I've tried to texture enough of them to find out that UV mapping is, while the the most precise, a rather contraining technique, though i use it for other models (architecture for example), I'm having trouble with organic ones. but i still don't give up.

At least you caught the only point I was trying to show: nurbs and subsurfaces need further developement.



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Joined: Fri Dec 06, 2002 9:47 am


Postby pa_furijaz » Wed Apr 02, 2003 10:51 am

I use Rhinoceros 3,0 for job and Blender for hobby every day. I have made various studies with Blender. The NURBS are better

NURBS Model Work in progress

Sub-Surf Model

My home Page Download car model


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