Quaternions, while powerful, are often misunderstood. Understanding these common misconceptions is crucial for correct application:
Misconception 1: Quaternion Multiplication is Commutative
Wrong: Many assume q₁ × q₂ = q₂ × q₁, like scalar multiplication.
Correct: Quaternion multiplication is non-commutative. The order matters significantly, especially in rotation composition. q₁ × q₂ represents applying rotation q₂ first, then q₁.
Misconception 2: All Quaternions Represent Rotations
Wrong: Any quaternion can be used for 3D rotations.
Correct: Only unit quaternions (|q| = 1) represent pure rotations. Non-unit quaternions represent combined rotation and scaling, which is usually undesired in 3D graphics.
Misconception 3: Quaternion Components Have Direct Geometric Meaning
Wrong: The w, x, y, z components directly correspond to rotation angles around axes.
Correct: While the vector part (x, y, z) relates to the rotation axis, the relationship is through trigonometric functions. For rotation θ around axis (x, y, z): q = (cos(θ/2), sin(θ/2)x, sin(θ/2)y, sin(θ/2)z).
Misconception 4: Quaternions are Just Another Angle Representation
Wrong: Quaternions are simply a different way to store rotation angles.
Correct: Quaternions form a mathematical group with unique properties. They provide advantages like avoiding gimbal lock, efficient composition, and smooth interpolation that other representations cannot match.