Importing Maya Nurbs

I'm learning Maya, and I'm convinced by comments in this Forum and elsewhere that I should concentrate on Nurbs for purposes of SL sculpties. But I'm still not sure whether some special script or software is required to upload a Maya Nurb and apply it as a texture to a prim in SL. Sometimes I read that a script or something is needed, and sometimes just that I should save the Nurb in Maya in the right format and then upload to SL and apply as a sculpty texture.

If I had the expertise of most people in this Forum, I wouldn't need to ask. Thank you!

Hello Flieger. Welcome to Maya land.

Before I answer your direct question, let me address a small terminology issue. There's no such thing as "a Nurb". NURBS is an acronym, which stands for "non-uniform rational Bezier spline". The S on the end does not make the word plural, nor does removing it make it singular. The S actually stands for the only noun in the whole phrase, "spline". All the other words are there simply to describe what kind of spline we're talking about. To omit the S is to omit the subject, leaving just a bunch of adjectives with nothing to describe, rendering the phrase nonsensical.

The correct terminology would be "a NURBS surface", or "a NURBS primitive", etc., not "a nurb".

Now that that's out of the way, on to your question. Take a look at this thread:, /8/06/257778/1.html. In it you'll find some basic tips for creating sculpty-compatible geometry with NURBS, and detailed instructions for how to export sculpt maps from Maya.




Oh and by the way, if you happen to be using the Personal Learning Edition of Maya, you'll need to purchase a licensed copy for sculpt map generation to work properly. PLE puts a watermark in all renderings, effectively makeing it useless for sculpt maps. You can still use PLE to learn how to use the program itself, but when it comes time to export your sculpties for SL, you'll need to upgrade to the real thing.

ur such a nurb, chosen

I very much appreciate your help and explanation. I have the licensed version of Maya, and so the only thing standing in the way of my exporting to SL is my brain. There's a lot to learn.

Thanks!

The "B" stands for Basis, which is usually shortened to B-spline.

That depends whom you ask. Both terms are correct. Some people call it a "Bezier spline" since Bezier invented it. Others call it a "basis spline", which is a more general term. See http://en.wikipedia.org/wiki/Nurbs for more information.

And yes, it's often abbreviate simply as B-spline. But since I was unfolding a larger abbreviation to begin with, I thought it would be rather incomplete to keep the B abbreviated while unabbreviating (if that's a word) all the other letters.

Ahh, ok. Here's the part from that article I'm guessing is confusing you: "non-uniform, rational B-splines are a generalization of Bézier splines". Which is not the same as saying Basic Splines is a general term for Bézier splines or that they are interchangeable. All this means is that NURBS are based on Bézier and other's, (just think we could be talking about Casteljau splines) work.

I'm also guessing you have not seen Bézier spline based surfaces. 3ds Max and some other apps have Bézier derived surfaces (patches), and although they share some similar characteristics, they are absolutely not NURBS.

So start telling those people you asked that no, Basic and Bézier are not interchangeable. Sorry.

All I know is I've seen it written both ways countless times. I didn't invent the acronym, nor was I present when whoever did invent it came up with it, and as far as I know, neither were you. So neither of us has any direct way of knowing what was or wasn't the intention. Here's what I'd like to see, if at all possible. If you have some source at your disposal that can definitively prove that the name Bezier absolutely does not belong in the acronym NURBS, please cite it. Otherwise, all I can go on is what I've always been taught, which I'll explain in the next paragraph.

My (somewhat fuzzy) understanding of how it all works is that a basis spline is simply a Bezier spline which has had some extra mathematical bells and whistles added to it to allow for spans and knots instead of just control points. Underneath that add-on, the core of the thing is still a Bezier spline (hence the B in NURBS can stand for either "basis" or "Bezier", although "basis" would be more the more pointed term). Further, what makes it "non-uniform" is the fact that the points don't have to be evenly spaced, and what makes it "rational" is that the ratio of polynomials in the mathematics is relevant (although I don't pretend to understand any of the math at all). If you can demonstrate that my knowledge here is in any way incorrect, please do so. As I said, I do not understand the mathematics.

I think I just corrected myself on my previous mis-statement that "basis spline" is a more general term than "Bezier spline". (Your guess was correct that that wording did get into my head after reading that Wikipedia article.) It would be better described, I think, not as a more general term, but as a more specific one, since every basis spline is a Bezier spline (under the hood) but not every Bezier spline is a basis spline. Would you agree with that assessment?

Definitively prove? Gosh, I wouldn't even know how to do that. Should we get a arbitration board or the International Standards Organization in on this or something? I'm only half joking when I wonder what it would take.

The wikipedia article you linked shows the B is for B-Spline which is short for Basis. All the boring computer graphics papers I read in school like this one http://web.cs.wpi.edu/~matt/courses/cs563/talks/nurbs.html had it as B-spline but I don't have them handy to cite. Hmm, the Maya help files indicate B-spline as well. The openNURBS website has a FAQ that lists them as B-Splines. Ok, seriously, what would it take?

How about this? Can you show me where it's been indicated that the B in NURBS is Bezier?

The mathematics for Bezier and B-Splines is similar in that one type can be converted to another, but I wouldn't say that it's technically accurate to portray a B-Spline as being a subset of Bezier splines. Here's a paper dealing with the differences if you are having trouble sleeping http://www.cs.umu.se/education/examina/Rapporter/461.pdf Regardless, this is nether here nor there as to what the NURBS B stands for, although note that it also has the NURBS "B" indicated as B-Spline

Man, this has totally burned up my pedant quota for the week.

Taken from the linked wiki article. Seems to more or less indicate a possible reference to B-Splines as Bezier Splines.
ETA:

Also, just farther in:

OK, the more I look, the more I'm finding references to "basis spline", and notably not finding references to "Bezier spline". I may have to concede defeat on this one. Perhaps my 3D teacher in college was smoking crack. It was, after all, he that claimed it stood for Bezier. Either that or my memory is faulty.

Thanks for the correction.

I know it's not a big deal, but this really has me curious now. I'll continue to dig, and I'll let you know what I find.

No problem Chosen, I know you would do the same for me



Le sigh.

Read the wiki again, follow the B-Spline link: "The term B-spline was coined by Isaac Jacob Schoenberg and is short for basis spline." Read the second link in my post above for the differences.

If I was making this up just to pull some sort of fast one here I would come up with a better name than that. Let me assure you it would be something along the lines of Bonedandyquadrodacious Spline and not the rather mundane name it has now.

They are not the same function. The results are similar, but it's like saying a .png is a .bmp (or a subset of .bmp) because they are both bitmap image formats.

Seriously guys, this is now going into my monthly pedant stock.

Sorry, meant to explain more but called away then forgot.

I didn't mean that that was any sort of thing declaring Chosen right, just that it seems to basically give the impression that Bezier Spline is at least accepted generally, if not completely and technically correct.

Personally, I'm content with just calling it a B-Spline, but that's just me =^B

No, it's ok I don't think there's anything to apologize about. You have me a bit confused. Do you think that I was trying to say that there is no such thing as a "Bezier spline?" Because, that's not what I was on about. All I am saying The B in NURBS is for Basis or B-Spline which is not the same as a Bezier Spline. B-Splines were developed because of deficiencies in Bezier splines.

This isn't about proving who's wrong and right with esoteric terms and theoretical math. I'm trying to tell folks there are real observable differences between how a Bezier surface or spline and NURBS surface or curve is implemented. I will admit if it was Joe Random SL User instead of Chosen I might not have corrected them, but Chosen is respected and listened to on these boards, so it pains me to see him give incorrect info.

This difference is provable to anyone who cares to do a bit of work. Maya doesn't have pure Bezier surfaces implemented so I guess you can't grok it if that's all you have ever used. Download the trial version of 3ds Max and model with the "patch" Bezier surfaces and then with the NURBS surfaces. Two different ways of doing kind of the same thing, but completely different in how they are done. Bezier surfaces are a poor man's NURBS surface.

I was trying to say that it seems that while it may be technically incorrect, Bezier Curve seems like it's being referenced as if it has become interchangeable with B-Spline and Basis-Spline to some extent, around the 3d community.

My internet has been borked lately, otherwise I'd be doing more thorough research myself to learn the differences, not necessarily mathematically, but practically, since I know that I don't understand the formulas used for NURBS at present.

Either way, whether you call it Basis or Bezier (And whether or not you are completely correct in either), I love NURBS. Just generally an awesome method in my mind. Polygons are nice, but.. I'll always prefer NURBS. Rhino ingrained that into my brain, even if I've moved on past Rhino

And now..to bed!

Me too. Thanks again for the correction, and thanks especially for the polite matter-of-fact way in which you presented it. By all means, if I'm incorrect on anything at any time, don't hesitate to speak up.