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How can I rotate a vector by a certain amount along a specific plane?

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I have three points in inertial space which is enough to specify a plane. I have a vector that lies in this plane, and would like to rotate this vector so that it becomes perpendicular with its original self, through a rotation about the plane. For example:
my points:
a=[1 .3 .5];
b=[0 0 0];
c=[4 5 6];
%plane passes through points a, b, and c, a is the vector to rotate
I mean to say a rotation on the plane (rotating with the pivot being the origin 0,0,0)

Accepted Answer

Alessandro Maria Laspina
Alessandro Maria Laspina on 3 Jun 2021
To find the vector that is in the same plane as the points c, a, and b, which is orthogonal to a we must:
1) first find the vector that is orthogonal to the plane CAB that passes through point b.
2) Rotate a about this vector 90 degrees.
To do this we can use the procedure described by @Bjorn Gustavsson(vector g is the plane that is orthogonal to plane c,a, and b)
Then, using the rodrigues equation (Rodrigues' rotation formula - Wikipedia), we plug in a for v, and k for g with theta being pi/2 and finally we obtain our correct vector.

More Answers (1)

Bjorn Gustavsson
Bjorn Gustavsson on 31 May 2021
Edited: Bjorn Gustavsson on 1 Jun 2021
Simply take another vector that lies in your plane, here c (you should understand why we can use c straight away). Then form an array that's in the plane but perpendicular to a:
d = c-dot(c,a)*a;
Then you get a vector that's perpendicular to a:
g = cross(a,d);
Here you'll have to plug in a normalization in order to not scale a. That was for rotating a out of the plane. For the rotation around the normal-vector of the plane you're close to done after the calculation of d - just normalize it to give it the same length as a.
Alessandro Maria Laspina
Alessandro Maria Laspina on 3 Jun 2021
Edited: Alessandro Maria Laspina on 3 Jun 2021
Thanks for the help, have a look at the answer- I may have complicated things a little bit but you definitely helped me get to where I needed.
Bjorn Gustavsson
Bjorn Gustavsson on 3 Jun 2021
OK, now I think I've fixed the typos properly. The correct equation should be:
d = c-dot(c,a/norm(a))*a/norm(a); % subtract the projection of c in the direction of a to get a vector perp to a
d = d*norm(a)/norm(d); % scaled to same length of a

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