Bezier Curves / Splines In Maya

[almakos]

Hi to all.
Afraid I am a bit offtopic, but have no idea where else to ask this questions:

1) Does Maya understand splines? or just Nurbs. If there is a way to make just usual spline, then how to do so?

2) Does anybody know how Maya makes Bezier curves?

I am interested in quadratic and cubic case.
Here on wiki are main formulas for Bezier curves, but what I need is to find out what coefficient Maya is using. In other words, how would that formulas look inside Maya.

I need that to recreate curve made in Maya outside program using info in exported dae file.

Hope I managed to explain clearly

Thanks.

[joojaa]

QUOTE
1) Does Maya understand splines? or just Nurbs. If there is a way to make just usual spline, then how to do so?

A NURBS curve IS a spline. So yes you can. Nurbs stands for Non uniform B spline, so while NURBS can describe all possible other spline types exactly beziers cant explain all nurbs curves, without a lot of extra points.

QUOTE
2) Does anybody know how Maya makes Bezier curves?

If split up a curve at each span you get a bezierspline, also if you adjust the parametrisation of a existing curve so that the multiplicity is varying so that each span is independent of next you get a bezierspline

QUOTE
but what I need is to find out what coefficient Maya is using

That is exactly the point of Nurbs to be able to set the coefficient yourself, for each point.

You trying to export into ai eps or something? Ive done that you know. Anyway care to tell us what you want to achieve theres most likely a very much faster way to do so.

[almakos]

Hi Joojaa.
Thank you for detailed answer.
Sorry, my questions were wrong. I will try to make it more clear.

Can I somehow get knots coordinates thorugh which curve is built instead of CV's when export?

[joojaa]

QUOTE(Almakos @ 03/23/09, 11:59 AM) [snapback]303686[/snapback]
Can I somehow get knots coordinates thorugh which curve is built instead of CV's when export?

Yes sure, just ask for them

[almakos]

It is not ai eps export, but yes quite similar situation. There are two possible ways for me to provide info.

First (ideal one) is to find dependency between CV's and knots.
When I check collada's dae file I see:

QUOTE
0 0 0 0.33333 0.33333 0 0.569114 1.3252 0.03299 1.56911 2.3252 0.03299 2.66667 2.66667 0 3 3 0
for control vertex
and this
QUOTE
0 0 0 0 1 2 3 3 3 3
for knots (edit points I believe)

or in .ma file
QUOTE
setAttr ".cc" -type "nurbsCurve"
3 3 0 no 3
8 0 0 0 1 2 3 3 3
6
0 0 0
0.33333000540733337 0.33333000540733337 0
0.5691144128333363 1.325196061602665 0.032990464412606002
1.5691144128333363 2.3251960616026635 0.032990464412606002
2.6666700839996338 2.6666700839996338 0
3 3 0
;

What I am trying to find out is how CV's vectors are linked (dependent) with knots in Maya.

Or another way. Not as good as first one.
To export knots coordinates vectors directly (that's is what I called splines in first post). I have no idea how to call them,...possibly write a MEL script which will put them in extra attributes which collada can export...

[joojaa]

QUOTE
for knots (edit points I believe)

Yes they are the each knot points parametrisation. The replication states that the end ponts are quaruplicated. They arent exactly edit points but they will lead to edit points. So they tell you at what wieghtings you will find a edit point.

But thing is if you read form files then this is not a api question, if you intend to use api then all you need to do is ask for its coordinates. Thing is tough for a nurbs surface at data is all you need to build the curcve as the edit point is derived form those. Not the other way around, offcourse you can make a feedback loop in most software to drive t the oppsote way around.

How to build the splines out fo the nurbs is not in teh scope of this forum

[almakos]

due to some strange error post arrived not complete, I have added missing lines, not so important now.

Thank you for explanation.