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View Full Version : problem Frenet frame?

HaVyThoai
12-28-2007, 11:15 AM
I just searched for Frenet frame and I got a Norway website. I don't understand its language but I can know its code.

http://www.ia.hiof.no/~borres/gb/ma-frames/p-frames.html

But there's a point I don't undestand,

that if use the fomula below

T=C'
B=T x C''
N=T x B
then Frenet frame look like this picture:
http://www.ia.hiof.no/~borres/gb/ma-frames/bcurve2.jpg

but If use the fomula

T=C'
B=T x V
N=T x B
with V=(0.0 , 0.0 , 1.0 , 0.0) then frenet frame would change like this picture
http://www.ia.hiof.no/~borres/gb/ma-frames/bcurve3.jpg

I don't understand. Please explain to me :)

datsua
12-29-2007, 02:20 PM
Hi,..
The problem with the first formula is that the 2nd derivative (i.e. C'') for the Bezier curve changes direction.

The second formula just takes a wild/educated guess at what C'' might be :)

You might also have a look at http://en.wikipedia.org/wiki/Derivative if you're not to familiar with derivatives.