Boundary of an orbit space. M is a 3-D domain that has a rotational symmetry. The thick circle represents a conductor, and the broken line shows the axis of rotation. The points of the axis constitute singular orbits, which are part of the boundary of the 2-D orbit space M/G.
Raumonen et al. Boundary Value Problems 2011 2011:9 doi:10.1186/1687-2770-2011-9