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The square of a quaternion rotation is a rotation by twice the angle around the same axis. More generally q n is a rotation by n times the angle around the same axis as q . This can be extended to arbitrary real n , allowing for smooth interpolation between spatial orientations; see Slerp .
Two reflections make a rotation by an angle twice the angle between the two reflection planes, so ′ ′ = corresponds to a rotation of 180° in the plane containing σ 1 and σ 2. This is very similar to the corresponding quaternion formula,
Like rotation matrices, quaternions must sometimes be renormalized due to rounding errors, to make sure that they correspond to valid rotations. The computational cost of renormalizing a quaternion, however, is much less than for normalizing a 3 × 3 matrix. Quaternions also capture the spinorial character of rotations in three dimensions.
where v is the rotation vector treated as a quaternion. A single multiplication by a versor, either left or right, is itself a rotation, but in four dimensions. Any four-dimensional rotation about the origin can be represented with two quaternion multiplications: one left and one right, by two different unit quaternions.
The connection between quaternions and rotations, commonly exploited in computer graphics, is explained in quaternions and spatial rotations. The map from S 3 onto SO(3) that identifies antipodal points of S 3 is a surjective homomorphism of Lie groups, with kernel {±1}. Topologically, this map is a two-to-one covering map. (See the plate trick.)
When a non-scalar quaternion is viewed as the quotient of two vectors, then the axis of the quaternion is a unit vector perpendicular to the plane of the two vectors in this original quotient, in a direction specified by the right hand rule. [59] The angle is the angle between the two vectors. In symbols, =.
There are two representations of quaternions. This article uses the more popular Hamilton. A quaternion has 4 real values: q w (the real part or the scalar part) and q x q y q z (the imaginary part). Defining the norm of the quaternion as follows: ‖ ‖ = + + +
The number of Euler angles needed to represent the group SO(n) is n(n − 1)/2, equal to the number of planes containing two distinct coordinate axes in n-dimensional Euclidean space. In SO(4) a rotation matrix is defined by two unit quaternions, and therefore has six degrees of freedom, three from each quaternion.