Re: Angle calculation from 3x3 matrix and 3x1 vector

In article <MPG.2305070de00f851e9896af@xxxxxxxxxxxxxx>, none@xxxxxxxx
says...
A vector does not have an orientation around itself. You need another
vector to give that. If you have a perpendicular n to the vector x, then
you can measure the rotation around vector x:

n' = (A^-1)^T n,

where ^-1 is for matrix inverse, ^T is for transpose. If A is a rotation
matrix (A^T = A^-1), then simply n' = A n.

cos(angle) = dot(n, n') / |n||n'|

Sorry, too fast typing, the last equation is incorrect.

First compute

p = n' - [dot(x, n') / dot(x, x)] x

Then

cos(angle) = dot(n, p) / |n||p|

This should do it.
.

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