Quaternions from and to other rotation representations — quat_from_axis

quat_from_axis_angle() / quat_to_axis_angle(): a rotation of angle radians about axis, counter-clockwise by the right-hand rule.
quat_from_matrix() / quat_to_matrix(): 3x3 rotation matrices, or a 3x3xn array with one matrix per row.

Usage

quat_from_axis_angle(axis, angle)

quat_to_axis_angle(q)

quat_from_matrix(rotation)

quat_to_matrix(q)

Arguments

axis: Axis vectors (length 3, or 3 columns); need not be unit length.
angle: Angles in radians.
q: Quaternions; see quaternions.
rotation: A 3x3 rotation matrix, or a 3x3xn array.

Value

quat_from_*(): a quaternion matrix. quat_to_axis_angle(): a list with axis (3 columns) and angle in [0, pi]; the axis of a zero rotation is NA. quat_to_matrix(): a 3x3xn array.

Examples

q <- quat_from_axis_angle(c(0, 0, 2), pi / 2)
quat_to_axis_angle(q)
#> $axis
#>      x y z
#> [1,] 0 0 1
#> 
#> $angle
#> [1] 1.570796
#> 
quat_to_matrix(q)[, , 1]
#>              [,1]          [,2] [,3]
#> [1,] 2.220446e-16 -1.000000e+00    0
#> [2,] 1.000000e+00  2.220446e-16    0
#> [3,] 0.000000e+00  0.000000e+00    1
quat_from_matrix(quat_to_matrix(q))
#>              w x y         z
#> [1,] 0.7071068 0 0 0.7071068