  In many situations it could be interesting to ascertain whether nonparametric
regression curves can be grouped, especially when confronted with a
considerable number of curves. The proposed testing procedure allows to
determine groups with an automatic selection of their number. A simulation
study is presented in order to investigate the finite sample properties of the
proposed methods when compared to existing alternative procedures. Finally, the
applicability of the procedure to study the geometry of a tunnel by analysing a
set of cross-sections is demonstrated. The results obtained show the existence
of some heterogeneity in the tunnel geometry.
