Construct n-dimensional rotation matrix.

src/base/cg.rs

@@ -69,6 +69,66 @@ where
     }
 }
 
+/// # Rotation in any dimension
+impl<T, D> OMatrix<T, D, D>
+where
+    T: RealField,
+    D: DimName,
+    DefaultAllocator: Allocator<T, D, D> + Allocator<T, D, U1> + Allocator<T, U1, D>,
+{
+    /// The n-dimensional rotation matrix described by an oriented minor arc.
+    ///
+    /// See [`Rotation::from_arc`](`crate::Rotation::from_arc`) for details.
+    #[must_use]
+    pub fn from_arc<SB, SC>(
+        from: &Unit<Vector<T, D, SB>>,
+        to: &Unit<Vector<T, D, SC>>,
+    ) -> Option<Self>
+    where
+        SB: Storage<T, D> + Clone,
+        SC: Storage<T, D> + Clone,
+    {
+        let (a, b, ab) = (from.as_ref(), to.as_ref(), from.dot(to));
+        let d = T::one() + ab;
+        (d > T::default_epsilon().sqrt()).then(|| {
+            let k = &(b * a.transpose() - a * b.transpose());
+            // Codesido's Rotation Formula
+            // <https://doi.org/10.14232/ejqtde.2018.1.13>
+            //
+            // Equals `Self::identity() + k + k * k / d`:
+            let mut r = Self::identity() + k;
+            r.gemm(d.recip(), k, k, T::one());
+            r
+        })
+    }
+    /// The n-dimensional rotation matrix described by an oriented minor arc and a signed angle.
+    ///
+    /// See [`Rotation::from_arc_angle`](`crate::Rotation::from_arc_angle`) for details.
+    #[must_use]
+    pub fn from_arc_angle<SB, SC>(
+        from: &Unit<Vector<T, D, SB>>,
+        to: &Unit<Vector<T, D, SC>>,
+        angle: T,
+    ) -> Option<Self>
+    where
+        SB: Storage<T, D> + Clone,
+        SC: Storage<T, D> + Clone,
+    {
+        let (a, b, ab) = (from.as_ref(), to.as_ref(), from.dot(to));
+        // Tries making `b` orthonormal to `a` via Gram-Schmidt process.
+        (b - a * ab)
+            .try_normalize(T::default_epsilon().sqrt())
+            .map(|ref b| {
+                let (sin, cos) = angle.sin_cos();
+                let [at, bt] = [&a.transpose(), &b.transpose()];
+                let [k1, k2] = [b * at - a * bt, -(a * at + b * bt)];
+                // Simple rotations / Rotation in a two–plane
+                // <https://doi.org/10.48550/arXiv.1103.5263>
+                Self::identity() + k1 * sin + k2 * (T::one() - cos)
+            })
+    }
+}
+
 /// # 2D transformations as a Matrix3
 impl<T: RealField> Matrix3<T> {
     /// Builds a 2 dimensional homogeneous rotation matrix from an angle in radian.

src/base/matrix.rs

@@ -81,6 +81,7 @@ pub type MatrixCross<T, R1, C1, R2, C2> =
 /// - [2D transformations as a Matrix3 <span style="float:right;">`new_rotation`…</span>](#2d-transformations-as-a-matrix3)
 /// - [3D transformations as a Matrix4 <span style="float:right;">`new_rotation`, `new_perspective`, `look_at_rh`…</span>](#3d-transformations-as-a-matrix4)
 /// - [Translation and scaling in any dimension <span style="float:right;">`new_scaling`, `new_translation`…</span>](#translation-and-scaling-in-any-dimension)
+/// - [Rotation in any dimension <span style="float:right;">`from_arc`, `from_arc_angle`</span>](#rotation-in-any-dimension)
 /// - [Append/prepend translation and scaling <span style="float:right;">`append_scaling`, `prepend_translation_mut`…</span>](#appendprepend-translation-and-scaling)
 /// - [Transformation of vectors and points <span style="float:right;">`transform_vector`, `transform_point`…</span>](#transformation-of-vectors-and-points)
 ///

src/geometry/rotation.rs

@@ -22,14 +22,14 @@ use rkyv::bytecheck;
 
 /// A rotation matrix.
 ///
-/// This is also known as an element of a Special Orthogonal (SO) group.
+/// This is also known as an element of a Special Orthogonal (SO) group. The [`Rotation`] type can
-/// The `Rotation` type can either represent a 2D or 3D rotation, represented as a matrix.
+/// represent an n-dimensional rotation as a matrix. For a rotation based on quaternions, see
-/// For a rotation based on quaternions, see [`UnitQuaternion`](crate::UnitQuaternion) instead.
+/// [`UnitQuaternion`](crate::UnitQuaternion) instead.
 ///
-/// Note that instead of using the [`Rotation`](crate::Rotation) type in your code directly, you should use one
+/// For fixed dimensions, you should use its aliases (e.g., [`Rotation2`](crate::Rotation2) or
-/// of its aliases: [`Rotation2`](crate::Rotation2), or [`Rotation3`](crate::Rotation3). Though
+/// [`Rotation3`](crate::Rotation3)) instead of the dimension-generic [`Rotation`](crate::Rotation)
-/// keep in mind that all the documentation of all the methods of these aliases will also appears on
+/// type. Though keep in mind that all the documentation of all the methods of these aliases will
-/// this page.
+/// also appears on this page.
 ///
 /// # Construction
 /// * [Identity <span style="float:right;">`identity`</span>](#identity)
@@ -38,6 +38,7 @@ use rkyv::bytecheck;
 /// * [From a 3D axis and/or angles <span style="float:right;">`new`, `from_euler_angles`, `from_axis_angle`…</span>](#construction-from-a-3d-axis-andor-angles)
 /// * [From a 3D eye position and target point <span style="float:right;">`look_at`, `look_at_lh`, `rotation_between`…</span>](#construction-from-a-3d-eye-position-and-target-point)
 /// * [From an existing 3D matrix or rotations <span style="float:right;">`from_matrix`, `rotation_between`, `powf`…</span>](#construction-from-an-existing-3d-matrix-or-rotations)
+/// * [From an arc in any dimension <span style="float:right;">`from_arc`, `from_arc_angle`…</span>](#construction-in-any-dimension)
 ///
 /// # Transformation and composition
 /// Note that transforming vectors and points can be done by multiplication, e.g., `rotation * point`.

src/geometry/rotation_alias.rs

@@ -2,10 +2,25 @@ use crate::geometry::Rotation;
 
 /// A 2-dimensional rotation matrix.
 ///
-/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type too.**
+/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type, too.**
 pub type Rotation2<T> = Rotation<T, 2>;
 
 /// A 3-dimensional rotation matrix.
 ///
-/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type too.**
+/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type, too.**
 pub type Rotation3<T> = Rotation<T, 3>;
+
+/// A 4-dimensional rotation matrix.
+///
+/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type, too.**
+pub type Rotation4<T> = Rotation<T, 4>;
+
+/// A 5-dimensional rotation matrix.
+///
+/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type, too.**
+pub type Rotation5<T> = Rotation<T, 5>;
+
+/// A 6-dimensional rotation matrix.
+///
+/// **Because this is an alias, not all its methods are listed here. See the [`Rotation`](crate::Rotation) type, too.**
+pub type Rotation6<T> = Rotation<T, 6>;

src/geometry/rotation_construction.rs

@@ -1,8 +1,8 @@
 use num::{One, Zero};
 
-use simba::scalar::{ClosedAdd, ClosedMul, SupersetOf};
+use simba::scalar::{ClosedAdd, ClosedMul, RealField, SupersetOf};
 
-use crate::base::{SMatrix, Scalar};
+use crate::base::{storage::Storage, Const, SMatrix, Scalar, Unit, Vector};
 
 use crate::geometry::Rotation;
 
@@ -44,6 +44,99 @@ where
     }
 }
 
+/// # Construction in any dimension
+impl<T: RealField, const D: usize> Rotation<T, D> {
+    /// The n-dimensional rotation matrix described by an oriented minor arc.
+    ///
+    /// This is the rotation `rot` aligning `from` with `to` over their minor angle such that
+    /// `(rot * from).angle(to) == 0` and `(rot * from).dot(to).is_positive()`.
+    ///
+    /// Returns `None` with `from` and `to` being anti-parallel. In contrast to
+    /// [`Self::from_arc_angle`], this method is robust for approximately parallel vectors
+    /// continuously approaching identity.
+    ///
+    /// See also [`OMatrix::from_arc`](`crate::OMatrix::from_arc`) for owned matrices generic over
+    /// storage.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[macro_use] extern crate approx;
+    /// # use nalgebra::{Rotation, Unit, Vector6};
+    /// let from = Unit::new_normalize(Vector6::new(-4.0, -2.4, 0.0, -3.3, -1.0, -9.0));
+    /// let to = Unit::new_normalize(Vector6::new(3.0, 1.0, 2.0, 2.0, 9.0, 6.0));
+    ///
+    /// // Aligns `from` with `to`.
+    /// let rot = Rotation::from_arc(&from, &to).unwrap();
+    /// assert_relative_eq!(rot * from, to, epsilon = 1.0e-6);
+    /// assert_relative_eq!(rot.inverse() * to, from, epsilon = 1.0e-6);
+    ///
+    /// // Returns identity with `from` and `to` being parallel.
+    /// let rot = Rotation::from_arc(&from, &from).unwrap();
+    /// assert_relative_eq!(rot, Rotation::identity(), epsilon = 1.0e-6);
+    ///
+    /// // Returns `None` with `from` and `to` being anti-parallel.
+    /// assert!(Rotation::from_arc(&from, &-from).is_none());
+    /// ```
+    #[must_use]
+    #[inline]
+    pub fn from_arc<SB, SC>(
+        from: &Unit<Vector<T, Const<D>, SB>>,
+        to: &Unit<Vector<T, Const<D>, SC>>,
+    ) -> Option<Self>
+    where
+        T: RealField,
+        SB: Storage<T, Const<D>> + Clone,
+        SC: Storage<T, Const<D>> + Clone,
+    {
+        SMatrix::from_arc(from, to).map(Self::from_matrix_unchecked)
+    }
+    /// The n-dimensional rotation matrix described by an oriented minor arc and a signed angle.
+    ///
+    /// Returns `None` with `from` and `to` being collinear. This method is more robust, the less
+    /// `from` and `to` are collinear, regardless of `angle`.
+    ///
+    /// See also [`Self::from_arc`] aligning `from` with `to` over their minor angle.
+    ///
+    /// See also [`OMatrix::from_arc_angle`](`crate::OMatrix::from_arc_angle`) for owned matrices
+    /// generic over storage.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[macro_use] extern crate approx;
+    /// # use nalgebra::{Rotation, Unit, Vector6};
+    /// let from = Unit::new_normalize(Vector6::new(1.0, 2.0, 3.0, 4.0, 5.0, 6.0));
+    /// let to = Unit::new_normalize(Vector6::new(3.0, 1.0, 2.0, 5.0, 9.0, 4.0));
+    ///
+    /// // Rotates by signed angle where `from` and `to` define its orientation.
+    /// let angle = 70f64.to_radians();
+    /// let rot = Rotation::from_arc_angle(&from, &to, angle).unwrap();
+    /// assert_relative_eq!((rot * from).angle(&from), angle, epsilon = 1.0e-6);
+    /// assert_relative_eq!((rot.inverse() * to).angle(&to), angle, epsilon = 1.0e-6);
+    /// let inv = Rotation::from_arc_angle(&from, &to, -angle).unwrap();
+    /// assert_relative_eq!(rot.inverse(), inv, epsilon = 1.0e-6);
+    ///
+    /// // Returns `None` with `from` and `to` being collinear.
+    /// assert!(Rotation::from_arc_angle(&from, &from, angle).is_none());
+    /// assert!(Rotation::from_arc_angle(&from, &-from, angle).is_none());
+    /// ```
+    #[must_use]
+    #[inline]
+    pub fn from_arc_angle<SB, SC>(
+        from: &Unit<Vector<T, Const<D>, SB>>,
+        to: &Unit<Vector<T, Const<D>, SC>>,
+        angle: T,
+    ) -> Option<Self>
+    where
+        T: RealField,
+        SB: Storage<T, Const<D>> + Clone,
+        SC: Storage<T, Const<D>> + Clone,
+    {
+        SMatrix::from_arc_angle(from, to, angle).map(Self::from_matrix_unchecked)
+    }
+}
+
 impl<T: Scalar, const D: usize> Rotation<T, D> {
     /// Cast the components of `self` to another type.
     ///