applyQuaternion( q ) {

		// quaternion q is assumed to have unit length

		const vx = this.x, vy = this.y, vz = this.z;
		const qx = q.x, qy = q.y, qz = q.z, qw = q.w;

		// t = 2 * cross( q.xyz, v );
		const tx = 2 * ( qy * vz - qz * vy );
		const ty = 2 * ( qz * vx - qx * vz );
		const tz = 2 * ( qx * vy - qy * vx );

		// v + q.w * t + cross( q.xyz, t );
		this.x = vx + qw * tx + qy * tz - qz * ty;
		this.y = vy + qw * ty + qz * tx - qx * tz;
		this.z = vz + qw * tz + qx * ty - qy * tx;

		return this;

	}
Applies the given Quaternion to this vector.

@param {Quaternion} q - The Quaternion.
@return {Vector3} A reference to this vector.