w
x
y
z
A rotation is a linear map R: ℝ³ → ℝ³ preserving length and orientation. The set of all valid rotations forms the group SO(3) — Special Orthogonal group in 3D.
R·Rᵀ = I (orthonormal columns)
det(R) = +1 (orientation-preserving)
9 parameters, 3 DOF (6 constraints)
q = [w, x, y, z], ‖q‖ = 1
R₀₀ = 1 - 2(y²+z²)
R₀₁ = 2(xy - wz)
R₀₂ = 2(xz + wy) ...
4 params, 3 DOF (unit constraint)
R = I + sin θ·[k]× + (1-cos θ)·[k]ײ
[k]× = skew-symmetric matrix of axis k
Minimal 3-param rep: θ·k̂
R = Rz(ψ) · Ry(θ) · Rx(φ)
ψ = yaw, θ = pitch, φ = roll
3 params, but NOT injective
q₁₂ = q₁ ⊗ q₂ (Hamilton product)
= [w₁w₂ - v₁·v₂,
w₁v₂ + w₂v₁ + v₁×v₂]
Equivalent to R₁ · R₂