Re: [Algorithms] Direction+Up vector to Axis/angle

[Jeff L. <je...@di...>]

You can convert a direction and up vector into a matrix very easily.  In fact they already are two thirds of the rotation matrix.  Recall that the columns of a rotation matrix define the local X,Y,and Z axes of the local frame.  With the up and direction you have Y and Z.  Take the cross product of those two to get X.  Then use Mr. Eberly's matrix->a&a code to get your result. (Of course I am assuming a Y-up world, but you get the idea)

Of course if you factor in the cross product into the matrix->a&a code you could probably optimize the whole thing a bit to give you an even more speedy routine, but that's up to you.

-Jeff

At 12:44 AM 11/22/2000 +0100, you wrote:
>Joe Ante wrote:
>
> > > Hello!
> > >
> > > Question: how to convert direction and up vectors to axis/angle
> > > rotation?
> > http://www.magic-software.com/Source/MgcCore3D/MgcMatrix3.cpp
>
>Excuse me maybe stupid question but what should I use from this class?
>It doesn't seem to deal with Axis/Angles except for set/get methods. My
>conversion method (matrix -> a&a) I have included seems to work OK.
>
>Today I spent another 5 hours trying to figure out how to convert
>this... damn direction/up vector to axis/angle. Help!! Maybe some code
>sample? I'm stuck.
>
>Thanks
>Max
>
>
>
>--
>-----------------------------------------------
>Max Gilead                     gi...@li...
>XMage library      http://xmage.sourceforge.net
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