Eigen::AngleAxisd

Eigen::AngleAxisd是Eigen库中用于描述3D旋转的类，它包含一个旋转角度和一个旋转轴向量。AngleAxisd的定义如下：

template<typename _Scalar>
class AngleAxis : public EigenBase<AngleAxis<_Scalar> >
{
public:
    typedef _Scalar Scalar;
    enum { Isometry = 0, Options = 0 };
    enum { Dim = 3, Axis = 0 };
    typedef Matrix<Scalar,3,1> Vector3;
    typedef Matrix<Scalar,4,1> Vector4;
    typedef Quaternion<Scalar> QuaternionType;
    typedef AngleAxis<Scalar> AngleAxisType;
    typedef Matrix<Scalar,3,3> Matrix3;
    typedef Matrix<Scalar,4,4> Matrix4;
    typedef Matrix<Scalar,Eigen::Dynamic,Eigen::Dynamic> DenseMatrix;
    typedef Matrix<Scalar,Eigen::Dynamic,1> DenseVector;
    AngleAxis() : m_angle(Scalar(0)), m_axis(Vector3::UnitX()) {}
    AngleAxis(const Quaternion<Scalar>& q);
    template<typename OtherScalar>
    explicit AngleAxis(const AngleAxis<OtherScalar>& other)
    {
        m_angle = static_cast<Scalar>(other.angle());
        m_axis = other.axis().template cast<Scalar>();
    }
    explicit AngleAxis(const Matrix<Scalar,3,1>& axis, Scalar angle)
        : m_angle(angle), m_axis(axis)
    {
        eigen_assert(axis.norm() > NumTraits<Scalar>::epsilon());
        m_axis.normalize();
    }
    explicit AngleAxis(Scalar roll, Scalar pitch, Scalar yaw);
    explicit AngleAxis(const Matrix<Scalar,3,3>& R);
    EIGEN_STRONG_INLINE const Scalar& angle() const { return m_angle; }
    EIGEN_STRONG_INLINE const Vector3& axis() const { return m_axis; }
    EIGEN_STRONG_INLINE QuaternionType toQuaternion() const
    {
        return QuaternionType(Eigen::AngleAxis<Scalar>(m_angle, m_axis));
    }
    EIGEN_STRONG_INLINE Matrix3 toRotationMatrix() const;
    static inline AngleAxisType Identity() { return AngleAxisType(); }
    EIGEN_STRONG_INLINE void setIdentity() { m_axis = Vector3::UnitX(); m_angle = Scalar(0); }
    bool operator==(const AngleAxisType& other) const
    {
        return m_angle == other.m_angle && m_axis == other.m_axis;
    }
    bool operator!=(const AngleAxisType& other) const
    {
        return m_angle != other.m_angle || m_axis != other.m_axis;
    }
private:
    Scalar m_angle;
    Vector3 m_axis;
};

其中，AngleAxisd的构造函数有多种形式，可以通过旋转角度和旋转轴向量来创建，也可以通过旋转矩阵或四元数来创建。此外，它还提供了一些方法，例如toQuaternion()用于将旋转向量转换为四元数，toRotationMatrix()用于将旋转向量转换为旋转矩阵等。