Add picture of torus mesh on the coarsest level

diff --git a/doc/doxygen/images/torus_manifold_ids.png b/doc/doxygen/images/torus_manifold_ids.png
new file mode 100644 (file)
index 0000000..3031f7c
Binary files /dev/null and b/doc/doxygen/images/torus_manifold_ids.png differ

diff --git a/include/deal.II/grid/grid_generator.h b/include/deal.II/grid/grid_generator.h
index 006577e0addbef5f91621ed7e5c32792329350e7..f1b0434d1ba6d8cefc6237db042bcf8d120ceaa2 100644 (file)
--- a/include/deal.II/grid/grid_generator.h
+++ b/include/deal.II/grid/grid_generator.h
@@ -1048,12 +1048,24 @@ namespace GridGenerator
    * If @p dim is 3, the mesh will be the volume of the torus, using a mesh
    * equivalent to the circle in the poloidal coordinates with 5 cells on the
    * cross section. This function attaches a TorusManifold to all boundary
-   * faces which are marked with a manifold id of 0, a CylindricalManifold to
+   * faces which are marked with a manifold id of 1, a CylindricalManifold to
    * the interior cells and all their faces which are marked with a manifold
    * id of 2 (representing a flat state within the poloidal coordinates), and
    * a TransfiniteInterpolationManifold to the cells between the TorusManifold
    * on the surface and the ToroidalManifold in the center, with cells marked
-   * with manifold id 1.
+   * with manifold id 0.
+   *
+   * An example for the case if @p dim is 3 with a cut through the domain at
+   * $z=0$, 6 toroidal cells, $R=2$ and $r=0.5$ without any global refinement
+   * is given here:
+   *
+   * @image html torus_manifold_ids.png
+   *
+   * In this picture, the light gray shade represents the manifold id 0 of the
+   * transfinite interpolation, which is applied to smoothly add new points
+   * between the toroidal shape on the domain boundary and the inner rim where
+   * a cylindrical description around the y-axis is prescribed. The inner rim
+   * with the manifold id 2 is shown in red shade.
    *
    * If @p dim is 2, the mesh will describe the surface of the torus and this
    * function attaches a TorusManifold to all cells and faces (which are