Degree 2 vs. 3 Curves and Hardness

[mikedin]

After experimenting with NURBS curves I've noticed that the create curves "text" in Maya only outputs degree 2 curves. The degree 2 curves also seem to have a common form; one CV is not "hard" then the next CV is "hard" and so on. I believe this is why they use the degree 2 curve for text shape generation, in that it allows any shape to be described Initially by using the soft then hard idea to control tangency. If one then convert this degree 2 curve to degree 3 it softens all the previous hard CV's and to make them hard again you need to place additional CV's at that location. Also if you manually "harden" CV's on a degree 2 it allows you to harden every CV but not a degree 3 which needs 2 CV's inbetween every hardenend CV. This is really hard to get a grasp on.

Lastly I can't find a section in the atribute editor or Maya GUI for that matter, that would show which CV's on a degree 3 or 2 etc. curve are "hardened."? It would make sense that hardening would add additional CV's to the existing ones location but that doesn't appear to be the case. Any help or tutorials on NURB shape construction and modification would be excellent indeed.

Thanks,

[jason-howey]

wow, you have definately opened my eyes to some of maya's limitations. I couldn't get an accurate rebuild either, so the only solution I was able to find was to hand draw a new cv curve with point snapping to the original text curves.
As for the hardness issue I do believe that it is possible to harden a CV without having to create additional CV's. I remember in Softimage 3.9 you were able to give custom weights to each CV in a nurbs curve or surface. if you gave it full weight it was like maya's "cv harden" but if you gave it no weight at all the CV didn't affect the curve what so ever.
I don't like maya's CV hardening at all, I can't find a way to un-harden it. also that every other cv harding thing you were talking about is another limitation. maya can't harden every point. it only hardens every other point on a 2 degree curve, but on a 3 degree curve it can only harden every third, and on a 7 degree curve it can only harden every seventh point!
So my advice on hardening is, just create multiple points in the same place. keep in mind that if you are using a 3 degree curve you'll need to put down 4 points in the same place to get that curve to be hard right there. if it's a 2 degree curve then you need 3 points, and a 5 degree curve needs 6 points.
So to sum it up, yes very annoying. (I don't have much more advice than that) I always thought that NURBS standing for Non-uniform Rational B-splines were non-uniform becuase you could non-uniformly weight the CV's but I guess not. Hopefully maya will change it's URBS, into NURBS in the next release.
best of luck!

[mikedin]

After more experimeting in "Maya 4.2." I found that you can unharden a CV but it's really not intuitive...

After you harden a CV on a degree 3(which has to have 2 adjacent non hard CV's next to it) you can then pick that CV again and apply a "CV Harden" to it with the "off" option. The bad thing is it doesn't appear to do a dang thing. Then if you go to the channel box and highlight "hardenPointX" it won't do anything still but...
If you then pick this node in the Atribute Editor you'll notice that the Harden point is set to "-1." if you set this to 1 it will be soft again and 2 a bit harder and 3 fully hard again. Appears only to be available in the AE...

BTW on a Degree 3 Curve; you only need 3 coincident CV's to harden this point.

Thanks for comfirming some of these issues.

[joojaa]

Well well you guys have noticed something but didnt realy understand what it is!

The reason why the import is such is that maya is making a nurbs surface that emulates bezier splines that are so common in 2d apps.

And a besier spline is just that each span seperated form the next span (open up illustrator an you oon realize that each inbetween is actualy 4 points). Se a nurbs surface can emulate beziers, and converted into one but the other way around is rather tricky tough, unles you make a besierized nurbs!!

Its noty a maya limitation but rather the limitation of beziers and rebuilding arbitraty curves. I realy dont understand why anyone would want to use beziers for anything its just carries so much more overhead!

Ok hope you understand better.

PS they are wighted. you can acces weighting trough mel.

[mikedin]

Well well you guys have noticed something but didnt realy understand what it is!

Funny you say that. Your explanation of beziers leads me to believe don't fully understand what they are!

Bezier curves are very simple low overhead descriptions of curves that have knots (like CV's but more close to EP points) that are allowed to have unique in and out tangents regardless of adjacent knots. The points you speak of are actually segments representing the curvature between knot tangents and you can have 1span tangents or as many as you deem necessary to create resolution of curviture. In max you can set a step setting between vertices of a bezier spline that will control your shape resolution e.g. with 4 bezier vertices and segements in between you can have a 1segment setting giving you a perfect square shapr or 6segement span giving you a circle. Illustrator doesn't use as an advanced bezier description as MAX and other apps.

Also NURBS are using a more advanced description of bezier curves so why you think they are high overhead alludes me... rational bezier splines.

Clearly the NURBS implementation in Maya is superior to MAX but FYI the MAX implementation is using true NURBS description and you are able to weight adjacent CV's of a NURBS curve and surface in MAX regardless of it's degree. Why not in Maya?

I have looked through the MEL script section and have done several searches for CV weighting but have only found 1 script which appears to be useless.

Would you mind pointing the "bezier" users to one these scripts.

This actually is in my opinion easier to edit complex shapes like text than Maya Nurbs.

[joojaa]

No im not realy rtaking about the overhead for solving the curve but rather the overhead for describing continioous surfaces. I know a bezier curve is pretty easy to solve. So is any nurbs! But some nurbs ops arent thet easy.

Maya can waight curves! Its not just implemented in the ui... go to the script section here and get a tool! Mel has tools for this and more!

Basicaly the difference is that each span in beziers is independent from the next! And may anurbs can decribe beziers if need be. But ass i said since maya uses nurbs algorithms to solve them then you just waste mem!

if you need beziers let maya rebuild your curve into one! The other way around isnt realy implementable!