PDA

View Full Version : Nurbs? Nurbs! Nurbs??



matd
12-11-2003, 06:21 AM
I've noticed this come up a couple of times in discussions here, where people have posted feature requests for "real NURBS".

My question is, all this while I thought I'd been using NURBS, but apparently I wasn't! (my only 3D experience is with LW which I've been using since 5.6) Could anyone tell me the difference between "real NURBS" and what LW has?

Cheers!:)

Dodgy
12-11-2003, 06:56 AM
Nurbs are Non Uniform Rational B-splines, a totally mathematical concept which used to be the main method of building organic objects. The way they did this was to apply other completely mathematical methods to splines (like we have in LW) such as lofting (like skin in LW, but you use multiple splines and the program interpolates between them) which don't change them into polys, but keep them as mathematically generated surfaces. This means they are completely smooth at render time, no sharp edges, no matter how close you get to them. However, most organic modelling is done now with subdivision surfaces like LW's 'nurbs'. Nurbs in LW are short hand for metanurbs, a subdivision method used in previous versions of lw.

Nurbs are used a lot in the architectural/product design world as they are resolution independent (no matter how small you go, you still have a definite curve) and so production lines can be generated from them.

matd
12-11-2003, 07:26 AM
what advantages do nurbs have over SubDs then? Or rather, why would people be requesting real NURBS as a feature in LW?

[edit: it's ok, re-read the last line of your post again!]

batzilla
12-11-2003, 12:44 PM
I think the tools used with nurbs modeling is faster than working with LW's tools.Maybe not faster but to me it has a better work flow.If you use the spline method in LW it tends to bog down with the rules of cross sections and such but with nurbs,being able to select them,then group them,then later lofting them keeps the screen from getting to complicated with polys and such.

I've been using Mayas nurbs modeling for about a month now and I love it.I do a lot of product modeling for 3 different companys and have always used LW but after the past month of learning how to model in Maya using nurbs,i'm totally sold on them(nurbs).

LW is a fantastic program and has the best poly modeling in the biz I think but for the work I do i'm going to be buying Maya in early January.Plus,learning another app is always a good thing.And I plan on spending next year learning character animation and I think Maya's pretty well equipt to handle that as well.

SplineGod
12-12-2003, 03:41 AM
In general NURBS modeling is a huge pain compared to modeling with SubDs which is why pretty much every 3D application has gone to them.
NURBS came into fashion when Alias was trying unsuccessfully to get its software into the movie making business years ago. The automakers in were interested in NURBS modeling because of its accurate surfaces which are great in manufacturing or print work but not that useful when creating images for movies or TV. To keep sales going Alias implemented NURBS for the engineering guys. Also in those days memory was very expensive and NURBS or splines in general use a lot less memory then polys.
Nowadays thats not a big deal.

I find LWs splines infinitely easier to use then NURBS. If you try and model with LW splines so that they autopatch its a pain and it feels more like NURBS modeling. I prefer to manually patch in LW which makes it MUCH easier and faster. In LW its very easy to mix splines and polys which is not something you can do with NURBS very easily. I can delete geometry, pick points, make splines and patch new polys where the old ones were.

And LW is great for character animation. Been doing it for years and LW8 has really pumped up the character tools. If you want to see some good discussion about LW splines check out this thread.
http://www.cgtalk.com/showthread.php?s=&threadid=104046

I think if I had to buy a modeling package for product design I would probably go with Rhino just because of cost. It supports NURBS.

sfriedberg
12-15-2003, 05:42 PM
NURBS are great, even indispensible, for some applications, but
They really aren't necessary for the sort of work that is usually done in Lightwave, and
They have some strong constraints on topology that limit how adjacent NURBS might be joined together, and
Control over meshes (for import into polygon-based programs) is somewhat haphazard.
I use an outstanding pure-NURBS modeler (Rhinoceros) when appropriate, but I wouldn't bother with Rhino for a lot of things. E.g., modeling a window frame with NURBS is sort of pointless.

While I wouldn't characterize NURBS modeling as a "huge pain", it probably is more time-consuming because you have to plan ahead to model complex surfaces successfully. It does not lend itself to just hacking out a face, and there is no equivalent to spin-quads to clean up topology if you get to a point where things don't match.

glassefx
12-17-2003, 08:18 AM
Originally posted by SplineGod
In general NURBS modeling is a huge pain compared to modeling with SubDs which is why pretty much every 3D application has gone to them.
NURBS came into fashion when Alias was trying unsuccessfully to get its software into the movie making business years ago. The automakers in were interested in NURBS modeling because of its accurate surfaces which are great in manufacturing or print work but not that useful when creating images for movies or TV. To keep sales going Alias implemented NURBS for the engineering guys. Also in those days memory was very expensive and NURBS or splines in general use a lot less memory then polys.
Nowadays thats not a big deal.

I find LWs splines infinitely easier to use then NURBS. If you try and model with LW splines so that they autopatch its a pain and it feels more like NURBS modeling. I prefer to manually patch in LW which makes it MUCH easier and faster. In LW its very easy to mix splines and polys which is not something you can do with NURBS very easily. I can delete geometry, pick points, make splines and patch new polys where the old ones were.

And LW is great for character animation. Been doing it for years and LW8 has really pumped up the character tools. If you want to see some good discussion about LW splines check out this thread.
http://www.cgtalk.com/showthread.php?s=&threadid=104046

I think if I had to buy a modeling package for product design I would probably go with Rhino just because of cost. It supports NURBS.

I totally agree but I always thought Nurb's held a big portion of the "movie-market" until sub-d's came into total evolultion in the past say 3 or 4 years? I say this because I see wires of movie shots on DVD's and such and a lot look like nurbs splines.

Also were'nt the dino's in JP modeled in Wavefront and animated with SI? Or the other way around?

My 2cw, Nurbs stink in comparisson to sub-d poly's unless your designing a car and people have to "extract" dimensions from your model. Also I'd like to say that nurbs are surface oriented vs. poly's free form exsistance which arent oriented in any specific manner.

Lightwolf
12-17-2003, 08:40 AM
Hi there...
Hm, but we already have spline patches...
Why not make them permanent and sticky in respect to the splines they wer created from. That would at least help those of us that need to create exact geometry (which can be a pain using SubDs).
Not all of us make our money with organic modelling, there is an industrial market out there as well, and LW is used in that segment too.
Cheers,
Mike

Exper
12-17-2003, 10:26 AM
Originally posted by Lightwolf
Hm, but we already have spline patches...
Why not make them permanent....Paraphrasing a very famous Dylan's song:

How many times we must ask for real splines /
Before NT will implement them /
The answer, my friend, is blowin' in the wind /
The answer is blowin' in the wind.

:D

Bye.

jin choung
12-17-2003, 11:18 PM
NURBS are significantly different and more robust than just as a real time version of lw's spline patches.

they are bloody fantastic if you need to SLICE AND DICE on your smooth surface!

one of the great advantages of nurbs that sds does NOT have is the ability to cut out any shape on your smooth surface... or even boolean two or more smooth surfaces.

sure, you could cut arbitrary patterns on sds... IF YOU TURN THEM INTO POLYS FIRST.

but with nurbs surfaces, you can keep the patches as higher order surfaces with a light geometry and YET still have cut out shapes on the smooth, generated surface.
------------------------------------------------------------------------------------

car chassis (and other industrial design forms) are perfect targets of nurbs modeling and will provide you the most flexibility all the way through from initial stages to end.

sure, many excellent EXCELLENT cars have been made with sds in lw but not without doing things in ways that i would argue are 'unnatural' and certainly inflexible.

think about the join of a modern car chassis to its protruding wheel well:

in sds, you either have to build them together and have the structure of the wheel well integrated into and interfere with the lines that the chassis is trying to follow.

OR

you can create the chassis in sds, freeze to polys, then boolean the polys. but then, you're stuck with your choice and if you need to modify later, you're SOL.

with nurbs, you can create the chassis. create the wheel well separately. no interference. then when you're ready, you simply slice out the form of the wheel well where it meets the car body, create a separation and BLEND (create a smooth join between two nurbs edges... another extremely nice feature).

you can undo the slice or the blend at any time, modify either the body or wheel well independently and remerge again without any fuss or muss.

IDEAL SOLUTION for car modeling.
------------------------------------------------------------------------------------

these advantages stem from the fact that nurbs are a PARAMETRIC surface... no other current geometry primitive, not even SDS is parametric -

that is, the surface is generated in such a way so that the computer 'KNOWS' where every point on the surface is.... that is why you can slice and dice... it knows exactly where on the surface you are cutting - at all times.

on a poly or sds, the software only knows where the surface is at the verts.
------------------------------------------------------------------------------------

NURBS are a standardized format and can go from app to app with not to much fuss.

SDS is NOT AT ALL STANDARDIZED!!! and to take a complete, textured and skinned sds model from one app to another is COMPLETELY IMPOSSIBLE without doing a lot of redundant work after an initial conversion of the cage.

this is one of the big reasons why studios still use nurbs... in a multi app environment, they are portable. not as portable and straightforward as straight polys for sure but still portable.
------------------------------------------------------------------------------------

but nurbs have limitations too. a single nurbs object is essentially a rectangular sheet.

if you can't make your object from a single deformed sheet, you must use MULTIPLE NURBS PATCHES to make you model.

this is unlike polys or sds where you can have arbitrary topology and have branching structures all over the place and still make it just one object.

multiple patches is STILL a problem on deforming models because when they deforem, they STILL tend to pull apart and create tears.

that is why i have always always ALWAYS felt that modeling characters with nurbs is an absolute ASSININE excercise in masochism.

but sometimes necessary if you need to go from one 3d app to another... again, ya just can't do that with sds without lots of redundant work.

jin

p.s. this must be like the tenth time i've written about the pros and cons of nurbs in the newtek forums and they all end up being just about this freakin' long. if i wasn't so lazy, i'd just go back and find one of my older posts and copy/paste but alas, i am just so lazy that i'd rather just re-type the whole shebang again.

sigh.

batzilla
12-18-2003, 12:57 AM
you da man jin : )

I ALWAYS dig reading your posts.You are obviously really knowledable and i've learned alot from your post.My brain isnt as big as yours yet but i'm working on it. : )

You're dead on with nurbs vs polys.I'm getting Maya in a month or so so I can get into nurbs(along w/character animating)I have Maya PLE and i'm loving it.Cant wait to model my first serious nurbs car.Theres so much about nurbs that seems so logical to me when modeling.I really dont like LW's subd's as much as Maya's. I always get that weird seam or crease with LW's subd's.And i'm not too fond of spinning quads.Too confusing at times.BTW,are LW's subd's REALLY subd's??? Maya seems to never have the creasing or seams problem that LW does.

Still havent made up my mind about continuing with LW.I love it but I dont think I can keep up with 2 3d apps.I'm thinking about selling my license after I get Maya to put towards some more software(Adobe digital video collection maybe).

I really love LW but I cant stay away from Maya PLE.Just personal preferance I guess.Theres alot to love about LW thats for sure.


Keep up the good advice Jin.BTW,I really like your little pic of you(?) getting jiggy.Cracks me up everytime I see it : )

jin choung
12-18-2003, 05:04 PM
hey batzilla,

wow... thanks for the really kind words. but rest assured that in actuality, i'm really really stupid. i'm certain you will easily surpass me within moments.

as for maya, yah, it is really really nice - and the price does reflect that. if you can afford it, i envy you!

i work with maya at work for rigging, skinning and animating and really the only modeling i've done in it is emergency remodels and such but i'm sure it is very capable.

i guess the only caveat i would throw out about maya is that be aware of the total cost of ownership. the 'complete' is about $2500 but the cost of future upgrades may be steeper than $500....

as for 'real subd's', i actually don't think there is such a thing. i would guess that PIXAR's would be the 'standard' since their guys actually developed the technology but because they own a patent, EVERY app other than maya (and i hear xsi) has rolled their own implementation - that includes c4d, truespace, mirai, etc....

and this lack of standardization as a result of patents is what makes sds so difficult in transporting in a multi-app work environment and why nurbs - while really odious for characters - is still used in this day and age.

as for lw's sds, yah it is different... but check out METAFORM PLUS which is in the legacy folder... it's NOT real time but it ends up creating less problems than lw's real time sds... much more like maya's.

in fact, it's my theory that the algorithm that's used in metaform plus IS the pixar algorithm exactly.... just not real time.

as for selling lw to get the adobe pack.... that's sounds sound to me.

but still, for personal preference, i MUCH prefer modeling in lw. in every other app (max, maya, etc.) because they have notions of OBJECTS in the main app, you always have to leap back and forth between object and 'sub object' and it just seems tedious to me.

but lots of super-professionals don't mind it so whichever way you decide to go, you should be set.

much luck and thanks again for the kind words - esp about the picture. everyone that i know personally is unmitigatingly horrified by it. :)

happy holidays,

jin

batzilla
12-18-2003, 06:26 PM
once again sound advice.

I'll try the metaforms +...never knew about it : /

Have a great holiday and keep pumping out the knowledge.

BTW,I think one way or another i'm gonna find a way to keep LW.Theres just too much I love about it.Wow,I remember the day I got Truespace and was on cloud nine.In a few months i'll have LW AND Maya! Never thought i'd have my head in two big dogs at once! : )

SplineGod
12-19-2003, 02:51 AM
I always get that weird seam or crease with LW's subd's.And i'm not too fond of spinning quads.Too confusing at times.BTW,are LW's subd's REALLY subd's??? Maya seems to never have the creasing or seams problem that LW does.


The weird seams are more likely opengl artifacts. I rarely ever have seams show up when rendering. Also the purpose of spin quads is to redirect the flow of the edges which is very important when organic modeling. Spin quads is not a good name for what it does. When I was at Siggraph demoing LW, I did some head modeling for several experienced character modelers who use Maya. The were extremely impressed with the speed and ease of LWs modeler for creating characters and EVERY single person I showed spin quads too was blown away with it. :)

batzilla
12-19-2003, 03:06 AM
My problem with spin quads is I have a hard time figuring out where to start.It seems that its something you just gottta get used to or something because it always takes me awhile to get it right.

As far as an opengl problem, its not because it shows up in the final render.As a matter of fact,even if I *freeze* the model it sometimes leaves the crease.Not often,but occasionally.If you look in the LW forums in the section where people post their WIPs you see this crease A LOT.I know that it takes more experience but to me its still something that should be fixed.I'm pretty experienced in LW's modeler(I have 3 pics in LW's Industrial section-perfume bottles) and the subd's still get on my nerves.

I love LW but I have to say that for me Maya is really awesome.I just like the way things *work*.I also think its modeling tools are fantastic.The only thing I miss in Maya is a bandsaw: ) I Didnt realise how often I used it until I started learning Maya.

jin choung
12-19-2003, 03:27 AM
well,

one of lw's greatest strengths with modeler right now seems to be its MASS OF TOOLS.

in maya, you have a few pull down menu worth of poly tools.

lw has an entire application filled with nothing but!

but having said that, you probably could replicate every lw tool in maya - speaking of which, you may be able to find bandsaw at highend3d or as a POLY BONUS PACK at alias proper.

as for the creases, they can be avoided but yah, there are algorithms out there that deal with problem areas more gracefully.... alas, metaform plus is better!

i for one end up using spin quads as well as spin tris (flay plugin) quite alot to great effect... and i don't even use sds for work (games....)!

jin

SplineGod
12-19-2003, 03:52 AM
Spin Quads (for me at least) are easy because I know where I want edges to go and this tool makes it simple to realign or change the flow. The edge common to both quads is the one thta is rotated.
As Jin pointed out theres lots of poly tools and while they can be replicated in Maya I still find LWs workflow to be fast and very very easy.
I also make it a point to not completely rely on one particular modeling tool. SubDs have their advantages but I tend to use splines, polys and subds in a sort of work triangle. Sometimes Ill rough out a form and flow with splines but then finish with SubDs. When I freeze the SubDs back to polys I may rework an area by deleteing the polys, creating splines from the exiting points and patch in a new section fo polys with either a modified form, flow or both.
Thats the great thing about LWs splines and SubDs is that they are really geared towards polys. Theres some huge advantages to that because there are no clear distinction between them.

glassefx
12-19-2003, 08:12 AM
Originally posted by jin choung
as for the creases, they can be avoided but yah, there are algorithms out there that deal with problem areas more gracefully.... alas, metaform plus is better!

jin

Yesh. I have always wondered why NT did'nt ever make it when you hit 'TAB' your not given the choice to use the two different smoothing algorithims instead of just the non-metaform method. Seems like no-biggie but I dont know of a way to load a lower density mesh into layout and have it do an 'automatic-metaform' on it like it does when you save a mesh thats been 'whatever it's called now.' With metaform a person has one more dimension to tweek to control tension. With the other way its the same tension over the whole model. Unless... and this is where I need to dwelve. Can one obtain metaform like results with a relativly simple mesh using weight-maps? For I am still learning the "new lightwave."
BTW - Yesh is not a typo. lol