SubDiv -> NURBS

[AAbel]

For me there are certrain shading networks, such as surface tangency based shading, that are much easier to implement on nurbs rather than subd's or poly's. With subd's to nurbs I can make my model with poly's convert it to nurbs, apply shader to nurbs, bake the results to a file, and apply that file to my poly/subd model. Also with this functionality we might see poly's get implemented into more pipelines at the bigger studios that are heavily dependant on nurbs. This functionality is going to really let us Maya users get the best of both worlds.

[GrafOrlok]

If it's an advantage or not I don't know, but when texturing NURBS you don't use UV's, or to be correct, your NURBS surface has got one U and one V direction. So a NURBS surface is essentially ALWAYS a square, whatever shape it has. And by using a square texture you always know where it will go. You can move it around on the surface but you can't go outside the surface boundaries.

But you can off course project it onto the surface and then these rules don't apply.

I feel NURBS are good for certain things, poly's for other and as long as you don't have to consider performance, SubD's for most stuff. Just wish the UV tools worked better on SubD's.

[Nonproductive]

What exactly is the difference between Subdivs and Nurbs from a modeling standpoint?

I am a novice at all of this but always thought that subdivs and nurbs were the same thing - controlling a large number of polys with a small number of edges/vertices.

I've toyed with Universe's UberNurbs and find them awesome to manipulate - are Maya's nurbs similar? Are Cinema 4D's similar?


thanks in advance!

[GrafOrlok]

Well, SubD's are much like working with Poly's. The best way (IMO) is to do a low poly model, maybe by using Connect Poly shape, and then, when you don't need to do anymore splits or extrudings, converting it to SubD's.

NURBS is a completely different way of modeling. It is more like shaping a square surface into the shape you want. You can also draw curves and loft between them to acheive the surface. You can also trim surfaces to get more flexibility, much like StudioTools works, but keep in mind: it is still always a square.

A hand is a typical object to model with polygons, while the sleeve is more a NURBS-job. You don't want to model a lot of protruding details such as fingers in a single NURBS mesh. When NURBS are used for objects such as hands and heads you often use patches stiching them together. But you always have the risk of the seams tearing when animated.

[Nonproductive]

thank you, Graf! Your explanation combined with a message from a thread in another forum here helped tremendously in my understanding the differences. :)

[alexx]

i see the differnce the follwing way:

subds are basically a way of modelling that combine the advantages of polies and nurbs in one way of modelling:
you have the flexibility of polies (resolution only where you need it - compared to isoparms in nurbs that stretch through your whole object; needed or not), the lightness of modelling with nurbs (your scene stays smaller than having a huge poly object since the base mesh of subds is or should be light). also you have the posibility to increase resolution of the object on render-time like with nurbs.

and honestly: if subds get faster and are more integrated (fur, painting, paint-sculpting...) i really think that nurbs is going to die since most models will be easier to be created in subds.
i see only very few reasons to use nurbs then anymore.
but that is only my oppinion. ;)

cheers

alexx

[Per-Anders]

I've not used SubD's in maya (and i've heard they're awful slow) but i do know that if you use Shave & Haircut it matches to SubD's, so that's hair/fur integration.

As far as texture/painting SubD's is concerned, well other packages manage it (deep Paint, BodyPaint), so we will have to wait and see with the new version of Maya. UV maps are still a pain though even with paint integration.

SubD paint sculpting... you can of course paint sculpt the lattice, but in order to paintsculpt the subd's themselves... hmm... not sure how possible that would be whilst retaining the editability/low res mesh... perhaps the old hack in maya of linking a smoothing node into a duplicate mesh might allow you to do this albeit without all of subd's features. Mebbe something for the future. Of course you can always paint a displacement map onto the poly's... interesting... might have to go and try and figure out if there's some way.

[-wT-]

That hack is also known as Connect PolyShape ;)

[dmcgrath]

Ive heard that the only renderer that supports Sub-d is Maya's native renderer. No one in the industry uses them yet. But you are right, there are LOTS of advantages to using them and someday Renderman will support them, then everyone will likely take advantage of what they offer.

[alexx]

Originally posted by dmcgrath
Ive heard that the only renderer that supports Sub-d is Maya's native renderer.

huh.. ?
did you just say that mayas renderer does something that no other renderer does? (besides crashing)

i need to sit down..
need to ..

I.. MUST.. KILL...

ohh.. :)
hehe

who am i and if yes how many?

[Per-Anders]

I'm not so sure of that claim... after all... lightwave, xsi, c4d, max etc all render subd's pretty well, and i'm reasonably certain that mental ray supports subd's according to it's feature list... prman also according to their page... but maybe this isn't true subd handling... i don't know... maybe it's maya's internal render engine is the only one to not handle subd's (well that is). lol

[alexx]

lightwave has subDs??

[Per-Anders]

has had for a long time at least since v 6 probably since v5... maya is pretty much the last of the packages to have subd's in their base package. full weighted subd's. handles them beautifully without significant slowdown either (lightwave that is).

[dmcgrath]

I set off a debate here, but really, I dont know everything, and dont claim to. But Maya's SubDs can only be rendered by Maya's renderer. This is what I have heard, and believe it will change in short time. I know other modeling programs have SubD but this is a Maya forum and was only speaking of Maya. I dont know L/W at all. Sorry for the confusion. :bounce:

[-wT-]

Yes, to my knowledge all other programs use more or less the same technique as CPS. Maya is the only one with hierarchial subds (So you can make smaller and smaller tweaks, go down the levels) which were first invented by Pixar... to my knowledge that is...

[Per-Anders]

having never used maya subd's i can't say for sure... but do you mean you can up the subd mesh resolution as and when?... cos you can do that in all the other packages... not entirely clear on the heirarchial subd's or what that means... is this something to do with maya's node history system?

[GrafOrlok]

Maya handles Subdivs very diferently than other packages. It's almost like working with poly's but it's like each polygon is a NURBS surface where you can add up to 13 detail levels. This means you can do a very low-poly model, convert it to subdivs and then detail it further by adding a finer level of detail on this particular "polygon". In theory you can build a head from a box and still it remains a box.

I have attached a pic from a project I've been working on and off on for a while and this is a perfect example of the advantage of using subdivs in Maya. The downside is that it takes forever for the surface to update when you animate;). I did a low-poly T-rex and then converted it to subdivs. Then I detailed the areas that needed more bumps, folds and wrinkles. I never needed to go further than level 3. On the left you see the low poly version and on the right the finished subdivision version.

[playmesumch00ns]

Other packages SubD's tend to be "Subdivided surfaces" which is just a polysmooth, or metaNURBS or whatever (tho MAX has a SubD surface type too?).

As Orlock said Maya has true (well, fairly true) Subdivision Surfaces based on its own SubD scheme whereas I think Pixar's ones are Catmull-Rom. Not sure if Edwin Catmull invented them, tho I assume so (genius!).

Subdivision surfaces are parametric surfaces, like NURBS, but you can add extra detail locally, like polys (using a knife tool or whatever). This is not the same as doing a smooth-subdivide operation on the polygons which adds more detail all over the mesh. In SubDs you start with your base mesh at level 0 and then "refine" a vertex, edge or face. This adds more vertices around it at the next level up in the heirachy with which you can add more detail, which you can then also refine and so on ad infinitum, or until your machine chugs to a halt.

Anyway these extra vertices are only visible at their respective detail levels, so in theory you could start off with a box-man, then model him up into a superhero using extra detail levels, then animate the box so you have like 20 vertices to worry about when skinning, but a beautifully detailed model appears on screen when rendered.

Also, since SubDs are parametric you will never, ever see a poly edge!

Since in Maya 4.5 we've now got a poly->NURBS function, going via SubD's, does that mean you could convert your poly model to subd's, then to NURBS, texture your NURBS model, taking advantage of the 0-1 parameter space, then convert back to SubD's for rendering? How would maya handle very complex shapes? would she split them into patches?

[S. J. Tubbrit]

Any chance we could see some more shots of that T_rex?

[GrafOrlok]

Sure, I'll see if I can post some in the WIP section when I get time off.

[-wT-]

Originally posted by playmesumch00ns
...How would maya handle very complex shapes? would she split them into patches?

Well what I've understood, that's exactly what she's doing, a NURBS-patch model.

Edit: Now when I think about it... doesn't Houdini use subdivs somewhat similiar to Maya's? Like, hierarchial that is?

[Per-Anders]

So am I correct in thinking that Maya SubD is basically (node or history we're looking at here) Your poly object, followed by a SubD node (visible) followed by some selection node into another subD node... etc etc... so you're basically building SubD's on top of SubD's using the history to go back and forth between different complexity levels? And each SubD object is in fact treated as a Poly object in it's own right once you move up a level?

Ok so that sounds cool if i've got that basic premise of it right... but what happens at the edges of your selection if you knife it? wont you get ngons and hence gaps? or do maya subd's handle ngons ok (or do you just have to be careful to not knife all the way to the edge of your selection)?

I think I kinda understand what you're saying, but it's just understanding what's going on in the background for this to happen.

[playmesumch00ns]

Yeah, that's sorta what happens, but there's only one node. The heirachical properties are intrinsic to SubD's nature. If you knife it or whatever, it works fine, but it's generally a better idea to keep it all quads where possible

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