Margus Ramst wrote in message <3722715b.0@news.povray.org>...
>Hey all you math-enabled people!
>I need a macro to give me the rotation vector to rotate vector A to have
the
>same direction as vector B. I suspect I could do it myself, but could
>somebody spare me the head-ache?


Interrupt me if I am wrong ;-) but do I understand you correctly?

You want to rotate a vector such, that it points in the same direction as
some other vector?

If so, I don't see the need for any rotational math. I would do it like
this:

Compute the length of vector A.
    lengthA = sqrt(Ax*Ax + Ay*Ay + Az*Az)

Normalize B to length 1. (B')
    lengthB = sqrt(Bx*Bx + Ay*Ay + Az*Az)
    B' = [ Bx/lengthB  By/lengthB  Bz/lengthB ]

Multiply it with the length of A (B'')
    B''= [ B'x*lengthA B'y*lengthA Bz*lengthA ]

B'' is now the same direction as B and with the length of A.

All in one formula:

            [ Bx / lengthB * lengthA ]
            [                        ]
   B'' =    [ By / lengthB * lengthA ]
            [                        ]
            [ Bz / lengthB * lengthA ]

(where lengthA and lengthB as given above)


Is that what you want?


Johannes.

P.S. So, I'm showing my math in public? I *really* hope I got it right ;-)

Post a reply to this message