Thread: Question about Confuted and Silvercord's 3D rotation tutorial.

  1. #1
    Registered User
    Join Date
    May 2010

    Question about Confuted and Silvercord's 3D rotation tutorial.

    Hi all.
    I've been reading through the Rotation Tutorials on this site at Part Three: Rotation About an Arbitrary Axis, and there's one point I'm not clear on.

    It says I should

    -Calculate the Perpendicular component, multiply it by the cosine of the angle you are trying to rotate through
    -Calculate the cross product between the vector you are trying to rotate about and the vector you are rotating, multiply it by the sine of the angle
    -Add the results together
    -Add the component of the vector you are trying to rotate that is parallel to the vector you are rotating about
    and then supplies a very handy rotation matrix.

    My question: Does multiplying my orientation vector by this matrix apply the above steps? Or should I do the steps and then apply the matrix to the result?

    If I do have to do these steps first, could someone please elaborate on the last one - "Add the component of the vector you are...." - I don't get it.

    Thanks for any help.
    Last edited by Inf_229; 05-02-2010 at 04:47 AM.

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    Looking there, I believe that matrix only does the rotation part, but the easy way to check would be to pick a vector, pick an axis, pick an angle, and see what kind of answer you get.

    To get the last part, you'll have to draw the picture. Pick an axis to rotate about, and some other vector. Do the rotation. You will draw a cone, with the axis of rotation being the center of the cone. The original vector can be represented in two parts -- the part going in the direction of the axis (the projection onto), and the part sticking out perpendicular (the perpendicular component, which is the radius of your cone). The radius part spins as your vector spins; the part down the middle stays the same. Hence you spin the radius part, then add in the constant part.

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