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Vector Computaion Problem

Started by Dakiar Dec 8, 2005 at 3:23 PM 1 replies 500+ views

Original Post

Dec 8, 2005 at 3:23 PM

I have two vectors A, and B and I want to know if I should rotate A clock-wise or counter-clock-wise to reach B as fast as possible. I rotate a ceratin amount of degrees each second. It's enough if it works with 2d vectors, even if a 3d formula would be nice too.. I have a way to compute this but it's very bad.. something beautiful would be very much appriciated!!

Zakwayda

1,120

Zakwayda

Dec 8, 2005 at 3:28 PM

In 2d you can find the signed angle between vectors of arbitrary non-zero length as:

angle = atan2(perpDot(a,b),dot(a,b));

In 3d you can find the unsigned angle as:

angle = atan2(length(cross(a,b)),dot(a,b));

To give the angle a sign in 3d, you need a reference vector; the sign of the angle is then the sign of the dot product of cross(a,b) with this reference vector. What makes sense to use as a reference vector depends on the circumstance.

Dakiar

Author

Dakiar

Dec 8, 2005 at 4:23 PM

Thank you so much, you've made my big bunch of code into a beautiful one-liner :D

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