nalgebra/src/geometry/rotation_specialization.rs

#[cfg(feature = "arbitrary")]
use crate::base::storage::Owned;
#[cfg(feature = "arbitrary")]
use quickcheck::{Arbitrary, Gen};

use num::Zero;

#[cfg(feature = "rand-no-std")]
use rand::{
    distributions::{uniform::SampleUniform, Distribution, OpenClosed01, Standard, Uniform},
    Rng,
};

use simba::scalar::RealField;
use simba::simd::{SimdBool, SimdRealField};
use std::ops::Neg;

use crate::base::dimension::{U1, U2, U3};
use crate::base::storage::Storage;
use crate::base::{
    Matrix2, Matrix3, SMatrix, SVector, Unit, UnitVector3, Vector, Vector1, Vector2, Vector3,
};

use crate::geometry::{Rotation2, Rotation3, UnitComplex, UnitQuaternion};

/*
 *
 * 2D Rotation matrix.
 *
 */
/// # Construction from a 2D rotation angle
impl<T: SimdRealField> Rotation2<T> {
    /// Builds a 2 dimensional rotation matrix from an angle in radian.
    ///
    /// # Example
    ///
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation2, Point2};
    /// let rot = Rotation2::new(f32::consts::FRAC_PI_2);
    ///
    /// assert_relative_eq!(rot * Point2::new(3.0, 4.0), Point2::new(-4.0, 3.0));
    /// ```
    pub fn new(angle: T) -> Self {
        let (sia, coa) = angle.simd_sin_cos();
        Self::from_matrix_unchecked(Matrix2::new(coa.clone(), -sia.clone(), sia, coa))
    }

    /// Builds a 2 dimensional rotation matrix from an angle in radian wrapped in a 1-dimensional vector.
    ///
    ///
    /// This is generally used in the context of generic programming. Using
    /// the `::new(angle)` method instead is more common.
    #[inline]
    pub fn from_scaled_axis<SB: Storage<T, U1>>(axisangle: Vector<T, U1, SB>) -> Self {
        Self::new(axisangle[0].clone())
    }
}

/// # Construction from an existing 2D matrix or rotations
impl<T: SimdRealField> Rotation2<T> {
    /// Builds a rotation from a basis assumed to be orthonormal.
    ///
    /// In order to get a valid rotation matrix, the input must be an
    /// orthonormal basis, i.e., all vectors are normalized, and the are
    /// all orthogonal to each other. These invariants are not checked
    /// by this method.
    pub fn from_basis_unchecked(basis: &[Vector2<T>; 2]) -> Self {
        let mat = Matrix2::from_columns(&basis[..]);
        Self::from_matrix_unchecked(mat)
    }

    /// Builds a rotation matrix by extracting the rotation part of the given transformation `m`.
    ///
    /// This is an iterative method. See `.from_matrix_eps` to provide mover
    /// convergence parameters and starting solution.
    /// This implements "A Robust Method to Extract the Rotational Part of Deformations" by Müller et al.
    pub fn from_matrix(m: &Matrix2<T>) -> Self
    where
        T: RealField,
    {
        Self::from_matrix_eps(m, T::default_epsilon(), 0, Self::identity())
    }

    /// Builds a rotation matrix by extracting the rotation part of the given transformation `m`.
    ///
    /// This implements "A Robust Method to Extract the Rotational Part of Deformations" by Müller et al.
    ///
    /// # Parameters
    ///
    /// * `m`: the matrix from which the rotational part is to be extracted.
    /// * `eps`: the angular errors tolerated between the current rotation and the optimal one.
    /// * `max_iter`: the maximum number of iterations. Loops indefinitely until convergence if set to `0`.
    /// * `guess`: an estimate of the solution. Convergence will be significantly faster if an initial solution close
    ///           to the actual solution is provided. Can be set to `Rotation2::identity()` if no other
    ///           guesses come to mind.
    pub fn from_matrix_eps(m: &Matrix2<T>, eps: T, mut max_iter: usize, guess: Self) -> Self
    where
        T: RealField,
    {
        if max_iter == 0 {
            max_iter = usize::max_value();
        }

        let mut rot = guess.into_inner();

        for _ in 0..max_iter {
            let axis = rot.column(0).perp(&m.column(0)) + rot.column(1).perp(&m.column(1));
            let denom = rot.column(0).dot(&m.column(0)) + rot.column(1).dot(&m.column(1));

            let angle = axis / (denom.abs() + T::default_epsilon());
            if angle.clone().abs() > eps {
                rot = Self::new(angle) * rot;
            } else {
                break;
            }
        }

        Self::from_matrix_unchecked(rot)
    }

    /// The rotation matrix required to align `a` and `b` but with its angle.
    ///
    /// This is the rotation `R` such that `(R * a).angle(b) == 0 && (R * a).dot(b).is_positive()`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Vector2, Rotation2};
    /// let a = Vector2::new(1.0, 2.0);
    /// let b = Vector2::new(2.0, 1.0);
    /// let rot = Rotation2::rotation_between(&a, &b);
    /// assert_relative_eq!(rot * a, b);
    /// assert_relative_eq!(rot.inverse() * b, a);
    /// ```
    #[inline]
    pub fn rotation_between<SB, SC>(a: &Vector<T, U2, SB>, b: &Vector<T, U2, SC>) -> Self
    where
        T: RealField,
        SB: Storage<T, U2>,
        SC: Storage<T, U2>,
    {
        crate::convert(UnitComplex::rotation_between(a, b).to_rotation_matrix())
    }

    /// The smallest rotation needed to make `a` and `b` collinear and point toward the same
    /// direction, raised to the power `s`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Vector2, Rotation2};
    /// let a = Vector2::new(1.0, 2.0);
    /// let b = Vector2::new(2.0, 1.0);
    /// let rot2 = Rotation2::scaled_rotation_between(&a, &b, 0.2);
    /// let rot5 = Rotation2::scaled_rotation_between(&a, &b, 0.5);
    /// assert_relative_eq!(rot2 * rot2 * rot2 * rot2 * rot2 * a, b, epsilon = 1.0e-6);
    /// assert_relative_eq!(rot5 * rot5 * a, b, epsilon = 1.0e-6);
    /// ```
    #[inline]
    pub fn scaled_rotation_between<SB, SC>(
        a: &Vector<T, U2, SB>,
        b: &Vector<T, U2, SC>,
        s: T,
    ) -> Self
    where
        T: RealField,
        SB: Storage<T, U2>,
        SC: Storage<T, U2>,
    {
        crate::convert(UnitComplex::scaled_rotation_between(a, b, s).to_rotation_matrix())
    }

    /// The rotation matrix needed to make `self` and `other` coincide.
    ///
    /// The result is such that: `self.rotation_to(other) * self == other`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation2;
    /// let rot1 = Rotation2::new(0.1);
    /// let rot2 = Rotation2::new(1.7);
    /// let rot_to = rot1.rotation_to(&rot2);
    ///
    /// assert_relative_eq!(rot_to * rot1, rot2);
    /// assert_relative_eq!(rot_to.inverse() * rot2, rot1);
    /// ```
    #[inline]
    #[must_use]
    pub fn rotation_to(&self, other: &Self) -> Self {
        other * self.inverse()
    }

    /// Ensure this rotation is an orthonormal rotation matrix. This is useful when repeated
    /// computations might cause the matrix from progressively not being orthonormal anymore.
    #[inline]
    pub fn renormalize(&mut self)
    where
        T: RealField,
    {
        let mut c = UnitComplex::from(self.clone());
        let _ = c.renormalize();

        *self = Self::from_matrix_eps(self.matrix(), T::default_epsilon(), 0, c.into())
    }

    /// Raise the rotation to a given floating power, i.e., returns the rotation with the angle
    /// of `self` multiplied by `n`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation2;
    /// let rot = Rotation2::new(0.78);
    /// let pow = rot.powf(2.0);
    /// assert_relative_eq!(pow.angle(), 2.0 * 0.78);
    /// ```
    #[inline]
    #[must_use]
    pub fn powf(&self, n: T) -> Self {
        Self::new(self.angle() * n)
    }
}

/// # 2D angle extraction
impl<T: SimdRealField> Rotation2<T> {
    /// The rotation angle.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation2;
    /// let rot = Rotation2::new(1.78);
    /// assert_relative_eq!(rot.angle(), 1.78);
    /// ```
    #[inline]
    #[must_use]
    pub fn angle(&self) -> T {
        self.matrix()[(1, 0)]
            .clone()
            .simd_atan2(self.matrix()[(0, 0)].clone())
    }

    /// The rotation angle needed to make `self` and `other` coincide.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation2;
    /// let rot1 = Rotation2::new(0.1);
    /// let rot2 = Rotation2::new(1.7);
    /// assert_relative_eq!(rot1.angle_to(&rot2), 1.6);
    /// ```
    #[inline]
    #[must_use]
    pub fn angle_to(&self, other: &Self) -> T {
        self.rotation_to(other).angle()
    }

    /// The rotation angle returned as a 1-dimensional vector.
    ///
    /// This is generally used in the context of generic programming. Using
    /// the `.angle()` method instead is more common.
    #[inline]
    #[must_use]
    pub fn scaled_axis(&self) -> SVector<T, 1> {
        Vector1::new(self.angle())
    }
}

#[cfg(feature = "rand-no-std")]
impl<T: SimdRealField> Distribution<Rotation2<T>> for Standard
where
    T::Element: SimdRealField,
    T: SampleUniform,
{
    /// Generate a uniformly distributed random rotation.
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Rotation2<T> {
        let twopi = Uniform::new(T::zero(), T::simd_two_pi());
        Rotation2::new(rng.sample(twopi))
    }
}

#[cfg(feature = "arbitrary")]
impl<T: SimdRealField + Arbitrary> Arbitrary for Rotation2<T>
where
    T::Element: SimdRealField,
    Owned<T, U2, U2>: Send,
{
    #[inline]
    fn arbitrary(g: &mut Gen) -> Self {
        Self::new(T::arbitrary(g))
    }
}

/*
 *
 * 3D Rotation matrix.
 *
 */
/// # Construction from a 3D axis and/or angles
impl<T: SimdRealField> Rotation3<T>
where
    T::Element: SimdRealField,
{
    /// Builds a 3 dimensional rotation matrix from an axis and an angle.
    ///
    /// # Arguments
    ///   * `axisangle` - A vector representing the rotation. Its magnitude is the amount of rotation
    ///   in radian. Its direction is the axis of rotation.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Point3, Vector3};
    /// let axisangle = Vector3::y() * f32::consts::FRAC_PI_2;
    /// // Point and vector being transformed in the tests.
    /// let pt = Point3::new(4.0, 5.0, 6.0);
    /// let vec = Vector3::new(4.0, 5.0, 6.0);
    /// let rot = Rotation3::new(axisangle);
    ///
    /// assert_relative_eq!(rot * pt, Point3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    /// assert_relative_eq!(rot * vec, Vector3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    ///
    /// // A zero vector yields an identity.
    /// assert_eq!(Rotation3::new(Vector3::<f32>::zeros()), Rotation3::identity());
    /// ```
    pub fn new<SB: Storage<T, U3>>(axisangle: Vector<T, U3, SB>) -> Self {
        let axisangle = axisangle.into_owned();
        let (axis, angle) = Unit::new_and_get(axisangle);
        Self::from_axis_angle(&axis, angle)
    }

    /// Builds a 3D rotation matrix from an axis scaled by the rotation angle.
    ///
    /// This is the same as `Self::new(axisangle)`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Point3, Vector3};
    /// let axisangle = Vector3::y() * f32::consts::FRAC_PI_2;
    /// // Point and vector being transformed in the tests.
    /// let pt = Point3::new(4.0, 5.0, 6.0);
    /// let vec = Vector3::new(4.0, 5.0, 6.0);
    /// let rot = Rotation3::new(axisangle);
    ///
    /// assert_relative_eq!(rot * pt, Point3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    /// assert_relative_eq!(rot * vec, Vector3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    ///
    /// // A zero vector yields an identity.
    /// assert_eq!(Rotation3::from_scaled_axis(Vector3::<f32>::zeros()), Rotation3::identity());
    /// ```
    pub fn from_scaled_axis<SB: Storage<T, U3>>(axisangle: Vector<T, U3, SB>) -> Self {
        Self::new(axisangle)
    }

    /// Builds a 3D rotation matrix from an axis and a rotation angle.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Point3, Vector3};
    /// let axis = Vector3::y_axis();
    /// let angle = f32::consts::FRAC_PI_2;
    /// // Point and vector being transformed in the tests.
    /// let pt = Point3::new(4.0, 5.0, 6.0);
    /// let vec = Vector3::new(4.0, 5.0, 6.0);
    /// let rot = Rotation3::from_axis_angle(&axis, angle);
    ///
    /// assert_eq!(rot.axis().unwrap(), axis);
    /// assert_eq!(rot.angle(), angle);
    /// assert_relative_eq!(rot * pt, Point3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    /// assert_relative_eq!(rot * vec, Vector3::new(6.0, 5.0, -4.0), epsilon = 1.0e-6);
    ///
    /// // A zero vector yields an identity.
    /// assert_eq!(Rotation3::from_scaled_axis(Vector3::<f32>::zeros()), Rotation3::identity());
    /// ```
    pub fn from_axis_angle<SB>(axis: &Unit<Vector<T, U3, SB>>, angle: T) -> Self
    where
        SB: Storage<T, U3>,
    {
        angle.clone().simd_ne(T::zero()).if_else(
            || {
                let ux = axis.as_ref()[0].clone();
                let uy = axis.as_ref()[1].clone();
                let uz = axis.as_ref()[2].clone();
                let sqx = ux.clone() * ux.clone();
                let sqy = uy.clone() * uy.clone();
                let sqz = uz.clone() * uz.clone();
                let (sin, cos) = angle.simd_sin_cos();
                let one_m_cos = T::one() - cos.clone();

                Self::from_matrix_unchecked(SMatrix::<T, 3, 3>::new(
                    sqx.clone() + (T::one() - sqx) * cos.clone(),
                    ux.clone() * uy.clone() * one_m_cos.clone() - uz.clone() * sin.clone(),
                    ux.clone() * uz.clone() * one_m_cos.clone() + uy.clone() * sin.clone(),
                    ux.clone() * uy.clone() * one_m_cos.clone() + uz.clone() * sin.clone(),
                    sqy.clone() + (T::one() - sqy) * cos.clone(),
                    uy.clone() * uz.clone() * one_m_cos.clone() - ux.clone() * sin.clone(),
                    ux.clone() * uz.clone() * one_m_cos.clone() - uy.clone() * sin.clone(),
                    uy * uz * one_m_cos + ux * sin,
                    sqz.clone() + (T::one() - sqz) * cos,
                ))
            },
            Self::identity,
        )
    }

    /// Creates a new rotation from Euler angles.
    ///
    /// The primitive rotations are applied in order: 1 roll − 2 pitch − 3 yaw.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation3;
    /// let rot = Rotation3::from_euler_angles(0.1, 0.2, 0.3);
    /// let euler = rot.euler_angles();
    /// assert_relative_eq!(euler.0, 0.1, epsilon = 1.0e-6);
    /// assert_relative_eq!(euler.1, 0.2, epsilon = 1.0e-6);
    /// assert_relative_eq!(euler.2, 0.3, epsilon = 1.0e-6);
    /// ```
    pub fn from_euler_angles(roll: T, pitch: T, yaw: T) -> Self {
        let (sr, cr) = roll.simd_sin_cos();
        let (sp, cp) = pitch.simd_sin_cos();
        let (sy, cy) = yaw.simd_sin_cos();

        Self::from_matrix_unchecked(SMatrix::<T, 3, 3>::new(
            cy.clone() * cp.clone(),
            cy.clone() * sp.clone() * sr.clone() - sy.clone() * cr.clone(),
            cy.clone() * sp.clone() * cr.clone() + sy.clone() * sr.clone(),
            sy.clone() * cp.clone(),
            sy.clone() * sp.clone() * sr.clone() + cy.clone() * cr.clone(),
            sy * sp.clone() * cr.clone() - cy * sr.clone(),
            -sp,
            cp.clone() * sr,
            cp * cr,
        ))
    }
}

/// # Construction from a 3D eye position and target point
impl<T: SimdRealField> Rotation3<T>
where
    T::Element: SimdRealField,
{
    /// Creates a rotation that corresponds to the local frame of an observer standing at the
    /// origin and looking toward `dir`.
    ///
    /// It maps the `z` axis to the direction `dir`.
    ///
    /// # Arguments
    ///   * dir - The look direction, that is, direction the matrix `z` axis will be aligned with.
    ///   * up - The vertical direction. The only requirement of this parameter is to not be
    ///   collinear to `dir`. Non-collinearity is not checked.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Vector3};
    /// let dir = Vector3::new(1.0, 2.0, 3.0);
    /// let up = Vector3::y();
    ///
    /// let rot = Rotation3::face_towards(&dir, &up);
    /// assert_relative_eq!(rot * Vector3::z(), dir.normalize());
    /// ```
    #[inline]
    pub fn face_towards<SB, SC>(dir: &Vector<T, U3, SB>, up: &Vector<T, U3, SC>) -> Self
    where
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        let zaxis = dir.normalize();
        let xaxis = up.cross(&zaxis).normalize();
        let yaxis = zaxis.cross(&xaxis).normalize();

        Self::from_matrix_unchecked(SMatrix::<T, 3, 3>::new(
            xaxis.x.clone(),
            yaxis.x.clone(),
            zaxis.x.clone(),
            xaxis.y.clone(),
            yaxis.y.clone(),
            zaxis.y.clone(),
            xaxis.z.clone(),
            yaxis.z.clone(),
            zaxis.z.clone(),
        ))
    }

    /// Deprecated: Use [`Rotation3::face_towards`] instead.
    #[deprecated(note = "renamed to `face_towards`")]
    pub fn new_observer_frames<SB, SC>(dir: &Vector<T, U3, SB>, up: &Vector<T, U3, SC>) -> Self
    where
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        Self::face_towards(dir, up)
    }

    /// Builds a right-handed look-at view matrix without translation.
    ///
    /// It maps the view direction `dir` to the **negative** `z` axis.
    /// This conforms to the common notion of right handed look-at matrix from the computer
    /// graphics community.
    ///
    /// # Arguments
    ///   * dir - The direction toward which the camera looks.
    ///   * up - A vector approximately aligned with required the vertical axis. The only
    ///   requirement of this parameter is to not be collinear to `dir`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Vector3};
    /// let dir = Vector3::new(1.0, 2.0, 3.0);
    /// let up = Vector3::y();
    ///
    /// let rot = Rotation3::look_at_rh(&dir, &up);
    /// assert_relative_eq!(rot * dir.normalize(), -Vector3::z());
    /// ```
    #[inline]
    pub fn look_at_rh<SB, SC>(dir: &Vector<T, U3, SB>, up: &Vector<T, U3, SC>) -> Self
    where
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        Self::face_towards(&dir.neg(), up).inverse()
    }

    /// Builds a left-handed look-at view matrix without translation.
    ///
    /// It maps the view direction `dir` to the **positive** `z` axis.
    /// This conforms to the common notion of left handed look-at matrix from the computer
    /// graphics community.
    ///
    /// # Arguments
    ///   * dir - The direction toward which the camera looks.
    ///   * up - A vector approximately aligned with required the vertical axis. The only
    ///   requirement of this parameter is to not be collinear to `dir`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use std::f32;
    /// # use nalgebra::{Rotation3, Vector3};
    /// let dir = Vector3::new(1.0, 2.0, 3.0);
    /// let up = Vector3::y();
    ///
    /// let rot = Rotation3::look_at_lh(&dir, &up);
    /// assert_relative_eq!(rot * dir.normalize(), Vector3::z());
    /// ```
    #[inline]
    pub fn look_at_lh<SB, SC>(dir: &Vector<T, U3, SB>, up: &Vector<T, U3, SC>) -> Self
    where
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        Self::face_towards(dir, up).inverse()
    }
}

/// # Construction from an existing 3D matrix or rotations
impl<T: SimdRealField> Rotation3<T>
where
    T::Element: SimdRealField,
{
    /// The rotation matrix required to align `a` and `b` but with its angle.
    ///
    /// This is the rotation `R` such that `(R * a).angle(b) == 0 && (R * a).dot(b).is_positive()`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Vector3, Rotation3};
    /// let a = Vector3::new(1.0, 2.0, 3.0);
    /// let b = Vector3::new(3.0, 1.0, 2.0);
    /// let rot = Rotation3::rotation_between(&a, &b).unwrap();
    /// assert_relative_eq!(rot * a, b, epsilon = 1.0e-6);
    /// assert_relative_eq!(rot.inverse() * b, a, epsilon = 1.0e-6);
    /// ```
    #[inline]
    pub fn rotation_between<SB, SC>(a: &Vector<T, U3, SB>, b: &Vector<T, U3, SC>) -> Option<Self>
    where
        T: RealField,
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        Self::scaled_rotation_between(a, b, T::one())
    }

    /// The smallest rotation needed to make `a` and `b` collinear and point toward the same
    /// direction, raised to the power `s`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Vector3, Rotation3};
    /// let a = Vector3::new(1.0, 2.0, 3.0);
    /// let b = Vector3::new(3.0, 1.0, 2.0);
    /// let rot2 = Rotation3::scaled_rotation_between(&a, &b, 0.2).unwrap();
    /// let rot5 = Rotation3::scaled_rotation_between(&a, &b, 0.5).unwrap();
    /// assert_relative_eq!(rot2 * rot2 * rot2 * rot2 * rot2 * a, b, epsilon = 1.0e-6);
    /// assert_relative_eq!(rot5 * rot5 * a, b, epsilon = 1.0e-6);
    /// ```
    #[inline]
    pub fn scaled_rotation_between<SB, SC>(
        a: &Vector<T, U3, SB>,
        b: &Vector<T, U3, SC>,
        n: T,
    ) -> Option<Self>
    where
        T: RealField,
        SB: Storage<T, U3>,
        SC: Storage<T, U3>,
    {
        // TODO: code duplication with Rotation.
        if let (Some(na), Some(nb)) = (a.try_normalize(T::zero()), b.try_normalize(T::zero())) {
            let c = na.cross(&nb);

            if let Some(axis) = Unit::try_new(c, T::default_epsilon()) {
                return Some(Self::from_axis_angle(&axis, na.dot(&nb).acos() * n));
            }

            // Zero or PI.
            if na.dot(&nb) < T::zero() {
                // PI
                //
                // The rotation axis is undefined but the angle not zero. This is not a
                // simple rotation.
                return None;
            }
        }

        Some(Self::identity())
    }

    /// The rotation matrix needed to make `self` and `other` coincide.
    ///
    /// The result is such that: `self.rotation_to(other) * self == other`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3};
    /// let rot1 = Rotation3::from_axis_angle(&Vector3::y_axis(), 1.0);
    /// let rot2 = Rotation3::from_axis_angle(&Vector3::x_axis(), 0.1);
    /// let rot_to = rot1.rotation_to(&rot2);
    /// assert_relative_eq!(rot_to * rot1, rot2, epsilon = 1.0e-6);
    /// ```
    #[inline]
    #[must_use]
    pub fn rotation_to(&self, other: &Self) -> Self {
        other * self.inverse()
    }

    /// Raise the rotation to a given floating power, i.e., returns the rotation with the same
    /// axis as `self` and an angle equal to `self.angle()` multiplied by `n`.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3, Unit};
    /// let axis = Unit::new_normalize(Vector3::new(1.0, 2.0, 3.0));
    /// let angle = 1.2;
    /// let rot = Rotation3::from_axis_angle(&axis, angle);
    /// let pow = rot.powf(2.0);
    /// assert_relative_eq!(pow.axis().unwrap(), axis, epsilon = 1.0e-6);
    /// assert_eq!(pow.angle(), 2.4);
    /// ```
    #[inline]
    #[must_use]
    pub fn powf(&self, n: T) -> Self
    where
        T: RealField,
    {
        if let Some(axis) = self.axis() {
            Self::from_axis_angle(&axis, self.angle() * n)
        } else if self.matrix()[(0, 0)] < T::zero() {
            let minus_id = SMatrix::<T, 3, 3>::from_diagonal_element(-T::one());
            Self::from_matrix_unchecked(minus_id)
        } else {
            Self::identity()
        }
    }

    /// Builds a rotation from a basis assumed to be orthonormal.
    ///
    /// In order to get a valid rotation matrix, the input must be an
    /// orthonormal basis, i.e., all vectors are normalized, and the are
    /// all orthogonal to each other. These invariants are not checked
    /// by this method.
    pub fn from_basis_unchecked(basis: &[Vector3<T>; 3]) -> Self {
        let mat = Matrix3::from_columns(&basis[..]);
        Self::from_matrix_unchecked(mat)
    }

    /// Builds a rotation matrix by extracting the rotation part of the given transformation `m`.
    ///
    /// This is an iterative method. See `.from_matrix_eps` to provide mover
    /// convergence parameters and starting solution.
    /// This implements "A Robust Method to Extract the Rotational Part of Deformations" by Müller et al.
    pub fn from_matrix(m: &Matrix3<T>) -> Self
    where
        T: RealField,
    {
        Self::from_matrix_eps(m, T::default_epsilon(), 0, Self::identity())
    }

    /// Builds a rotation matrix by extracting the rotation part of the given transformation `m`.
    ///
    /// This implements "A Robust Method to Extract the Rotational Part of Deformations" by Müller et al.
    ///
    /// # Parameters
    ///
    /// * `m`: the matrix from which the rotational part is to be extracted.
    /// * `eps`: the angular errors tolerated between the current rotation and the optimal one.
    /// * `max_iter`: the maximum number of iterations. Loops indefinitely until convergence if set to `0`.
    /// * `guess`: a guess of the solution. Convergence will be significantly faster if an initial solution close
    ///           to the actual solution is provided. Can be set to `Rotation3::identity()` if no other
    ///           guesses come to mind.
    pub fn from_matrix_eps(m: &Matrix3<T>, eps: T, mut max_iter: usize, guess: Self) -> Self
    where
        T: RealField,
    {
        if max_iter == 0 {
            max_iter = usize::MAX;
        }

        // Using sqrt(eps) ensures we perturb with something larger than eps; clamp to eps to handle the case of eps > 1.0
        let eps_disturbance = eps.clone().sqrt().max(eps.clone() * eps.clone());
        let mut perturbation_axes = Vector3::x_axis();
        let mut rot = guess.into_inner();

        for _ in 0..max_iter {
            let axis = rot.column(0).cross(&m.column(0))
                + rot.column(1).cross(&m.column(1))
                + rot.column(2).cross(&m.column(2));
            let denom = rot.column(0).dot(&m.column(0))
                + rot.column(1).dot(&m.column(1))
                + rot.column(2).dot(&m.column(2));

            let axisangle = axis / (denom.abs() + T::default_epsilon());

            if let Some((axis, angle)) = Unit::try_new_and_get(axisangle, eps.clone()) {
                rot = Rotation3::from_axis_angle(&axis, angle) * rot;
            } else {
                // Check if stuck in a maximum w.r.t. the norm (m - rot).norm()
                let mut perturbed = rot.clone();
                let norm_squared = (m - &rot).norm_squared();
                let mut new_norm_squared: T;

                // Perturb until the new norm is significantly different
                loop {
                    perturbed *=
                        Rotation3::from_axis_angle(&perturbation_axes, eps_disturbance.clone());
                    new_norm_squared = (m - &perturbed).norm_squared();
                    if abs_diff_ne!(
                        norm_squared,
                        new_norm_squared,
                        epsilon = T::default_epsilon()
                    ) {
                        break;
                    }
                }

                // If new norm is larger, it's a minimum
                if norm_squared < new_norm_squared {
                    break;
                }

                // If not, continue from perturbed rotation, but use a different axes for the next perturbation
                perturbation_axes = UnitVector3::new_unchecked(perturbation_axes.yzx());
                rot = perturbed;
            }
        }

        Self::from_matrix_unchecked(rot)
    }

    /// Ensure this rotation is an orthonormal rotation matrix. This is useful when repeated
    /// computations might cause the matrix from progressively not being orthonormal anymore.
    #[inline]
    pub fn renormalize(&mut self)
    where
        T: RealField,
    {
        let mut c = UnitQuaternion::from(self.clone());
        let _ = c.renormalize();

        *self = Self::from_matrix_eps(self.matrix(), T::default_epsilon(), 0, c.into())
    }
}

/// # 3D axis and angle extraction
impl<T: SimdRealField> Rotation3<T> {
    /// The rotation angle in [0; pi].
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Unit, Rotation3, Vector3};
    /// let axis = Unit::new_normalize(Vector3::new(1.0, 2.0, 3.0));
    /// let rot = Rotation3::from_axis_angle(&axis, 1.78);
    /// assert_relative_eq!(rot.angle(), 1.78);
    /// ```
    #[inline]
    #[must_use]
    pub fn angle(&self) -> T {
        ((self.matrix()[(0, 0)].clone()
            + self.matrix()[(1, 1)].clone()
            + self.matrix()[(2, 2)].clone()
            - T::one())
            / crate::convert(2.0))
        .simd_acos()
    }

    /// The rotation axis. Returns `None` if the rotation angle is zero or PI.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3, Unit};
    /// let axis = Unit::new_normalize(Vector3::new(1.0, 2.0, 3.0));
    /// let angle = 1.2;
    /// let rot = Rotation3::from_axis_angle(&axis, angle);
    /// assert_relative_eq!(rot.axis().unwrap(), axis);
    ///
    /// // Case with a zero angle.
    /// let rot = Rotation3::from_axis_angle(&axis, 0.0);
    /// assert!(rot.axis().is_none());
    /// ```
    #[inline]
    #[must_use]
    pub fn axis(&self) -> Option<Unit<Vector3<T>>>
    where
        T: RealField,
    {
        let rotmat = self.matrix();
        let axis = SVector::<T, 3>::new(
            rotmat[(2, 1)].clone() - rotmat[(1, 2)].clone(),
            rotmat[(0, 2)].clone() - rotmat[(2, 0)].clone(),
            rotmat[(1, 0)].clone() - rotmat[(0, 1)].clone(),
        );

        Unit::try_new(axis, T::default_epsilon())
    }

    /// The rotation axis multiplied by the rotation angle.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3, Unit};
    /// let axisangle = Vector3::new(0.1, 0.2, 0.3);
    /// let rot = Rotation3::new(axisangle);
    /// assert_relative_eq!(rot.scaled_axis(), axisangle, epsilon = 1.0e-6);
    /// ```
    #[inline]
    #[must_use]
    pub fn scaled_axis(&self) -> Vector3<T>
    where
        T: RealField,
    {
        if let Some(axis) = self.axis() {
            axis.into_inner() * self.angle()
        } else {
            Vector::zero()
        }
    }

    /// The rotation axis and angle in ]0, pi] of this rotation matrix.
    ///
    /// Returns `None` if the angle is zero.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3, Unit};
    /// let axis = Unit::new_normalize(Vector3::new(1.0, 2.0, 3.0));
    /// let angle = 1.2;
    /// let rot = Rotation3::from_axis_angle(&axis, angle);
    /// let axis_angle = rot.axis_angle().unwrap();
    /// assert_relative_eq!(axis_angle.0, axis);
    /// assert_relative_eq!(axis_angle.1, angle);
    ///
    /// // Case with a zero angle.
    /// let rot = Rotation3::from_axis_angle(&axis, 0.0);
    /// assert!(rot.axis_angle().is_none());
    /// ```
    #[inline]
    #[must_use]
    pub fn axis_angle(&self) -> Option<(Unit<Vector3<T>>, T)>
    where
        T: RealField,
    {
        self.axis().map(|axis| (axis, self.angle()))
    }

    /// The rotation angle needed to make `self` and `other` coincide.
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::{Rotation3, Vector3};
    /// let rot1 = Rotation3::from_axis_angle(&Vector3::y_axis(), 1.0);
    /// let rot2 = Rotation3::from_axis_angle(&Vector3::x_axis(), 0.1);
    /// assert_relative_eq!(rot1.angle_to(&rot2), 1.0045657, epsilon = 1.0e-6);
    /// ```
    #[inline]
    #[must_use]
    pub fn angle_to(&self, other: &Self) -> T
    where
        T::Element: SimdRealField,
    {
        self.rotation_to(other).angle()
    }

    /// Creates Euler angles from a rotation.
    ///
    /// The angles are produced in the form (roll, pitch, yaw).
    #[deprecated(note = "This is renamed to use `.euler_angles()`.")]
    pub fn to_euler_angles(self) -> (T, T, T)
    where
        T: RealField,
    {
        self.euler_angles()
    }

    /// Euler angles corresponding to this rotation from a rotation.
    ///
    /// The angles are produced in the form (roll, pitch, yaw).
    ///
    /// # Example
    /// ```
    /// # #[macro_use] extern crate approx;
    /// # use nalgebra::Rotation3;
    /// let rot = Rotation3::from_euler_angles(0.1, 0.2, 0.3);
    /// let euler = rot.euler_angles();
    /// assert_relative_eq!(euler.0, 0.1, epsilon = 1.0e-6);
    /// assert_relative_eq!(euler.1, 0.2, epsilon = 1.0e-6);
    /// assert_relative_eq!(euler.2, 0.3, epsilon = 1.0e-6);
    /// ```
    #[must_use]
    pub fn euler_angles(&self) -> (T, T, T)
    where
        T: RealField,
    {
        // Implementation informed by "Computing Euler angles from a rotation matrix", by Gregory G. Slabaugh
        //  https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.371.6578
        if self[(2, 0)].clone().abs() < T::one() {
            let yaw = -self[(2, 0)].clone().asin();
            let roll = (self[(2, 1)].clone() / yaw.clone().cos())
                .atan2(self[(2, 2)].clone() / yaw.clone().cos());
            let pitch = (self[(1, 0)].clone() / yaw.clone().cos())
                .atan2(self[(0, 0)].clone() / yaw.clone().cos());
            (roll, yaw, pitch)
        } else if self[(2, 0)].clone() <= -T::one() {
            (
                self[(0, 1)].clone().atan2(self[(0, 2)].clone()),
                T::frac_pi_2(),
                T::zero(),
            )
        } else {
            (
                -self[(0, 1)].clone().atan2(-self[(0, 2)].clone()),
                -T::frac_pi_2(),
                T::zero(),
            )
        }
    }
}

#[cfg(feature = "rand-no-std")]
impl<T: SimdRealField> Distribution<Rotation3<T>> for Standard
where
    T::Element: SimdRealField,
    OpenClosed01: Distribution<T>,
    T: SampleUniform,
{
    /// Generate a uniformly distributed random rotation.
    #[inline]
    fn sample<'a, R: Rng + ?Sized>(&self, rng: &mut R) -> Rotation3<T> {
        // James Arvo.
        // Fast random rotation matrices.
        // In D. Kirk, editor, Graphics Gems III, pages 117-120. Academic, New York, 1992.

        // Compute a random rotation around Z
        let twopi = Uniform::new(T::zero(), T::simd_two_pi());
        let theta = rng.sample(&twopi);
        let (ts, tc) = theta.simd_sin_cos();
        let a = SMatrix::<T, 3, 3>::new(
            tc.clone(),
            ts.clone(),
            T::zero(),
            -ts,
            tc,
            T::zero(),
            T::zero(),
            T::zero(),
            T::one(),
        );

        // Compute a random rotation *of* Z
        let phi = rng.sample(&twopi);
        let z = rng.sample(OpenClosed01);
        let (ps, pc) = phi.simd_sin_cos();
        let sqrt_z = z.clone().simd_sqrt();
        let v = Vector3::new(pc * sqrt_z.clone(), ps * sqrt_z, (T::one() - z).simd_sqrt());
        let mut b = v.clone() * v.transpose();
        b += b.clone();
        b -= SMatrix::<T, 3, 3>::identity();

        Rotation3::from_matrix_unchecked(b * a)
    }
}

#[cfg(feature = "arbitrary")]
impl<T: SimdRealField + Arbitrary> Arbitrary for Rotation3<T>
where
    T::Element: SimdRealField,
    Owned<T, U3, U3>: Send,
    Owned<T, U3>: Send,
{
    #[inline]
    fn arbitrary(g: &mut Gen) -> Self {
        Self::new(SVector::arbitrary(g))
    }
}