Deprecate Point as axis.

doc/news/changes/incompatibilities/20211011Fehling

@@ -1,5 +1,7 @@
 Changed: The 3D implementation of GridTools::rotate() with an integer
 for a Certesian coordinate direction has been superseded by the version
-that accepts unit vectors as rotation axes.
+that accepts unit vectors as rotation axes. Further,
+Physics::Transformations::Rotations::rotation_matrix_3d() now requires
+a Tensor<1,3> object instead of a Point<3> as an axis.
 <br>
 (Marc Fehling, 2021/10/11)

include/deal.II/physics/transformations.h

@@ -91,6 +91,15 @@ namespace Physics
       Tensor<2, 3, Number>
       rotation_matrix_3d(const Tensor<1, 3, Number> &axis, const Number &angle);
 
+      /**
+       * @copydoc Physics::Transformations::Rotations::rotation_matrix_3d()
+       *
+       * @deprecated Use the variant with a Tensor as an axis.
+       */
+      template <typename Number>
+      DEAL_II_DEPRECATED_EARLY Tensor<2, 3, Number>
+      rotation_matrix_3d(const Point<3, Number> &axis, const Number &angle);
+
       //@}
 
     } // namespace Rotations
@@ -935,6 +944,17 @@ Physics::Transformations::Rotations::rotation_matrix_3d(
 
 
 
+template <typename Number>
+Tensor<2, 3, Number>
+Physics::Transformations::Rotations::rotation_matrix_3d(
+  const Point<3, Number> &axis,
+  const Number &          angle)
+{
+  return rotation_matrix_3d(static_cast<Tensor<1, 3, Number>>(axis), angle);
+}
+
+
+
 template <int dim, typename Number>
 inline Tensor<1, dim, Number>
 Physics::Transformations::Contravariant::push_forward(