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Couple of quickies...

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Hi Guys, couple of questions I seek your aid with :-) Am converting an objects world velocity to object velocity and back again. Am using the following equation: Vx = cos(theta) * World_Vz + sin(theta) * World_Vx Vz = -sin(theta) * World_Vz + cos(theta) * World_Vx And to convert it back again I''m doing the same thing but replace Vx with World_Vx and vice versa. Anyone got the proof as to why this works?

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It looks like you are essentially multiplying your vectors by the 2x2 rotation matrix

cos(theta) sin(theta)
-sin(theta) cos(theta)

which rotates them into the local space of the matrix. The two rows of the matrix are orthogonal basis vectors in 2D, representing the local coordinate system of your object. If you don''t know about matrices already, you might be interested in learning about them, as they can speed up and make more elegant computations like the one you''re doing here (although in this case it wouldn''t make much difference). One good reference is "3D Math Primer" by Dunn and Parberry.

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