On continuum real trees of circle maps and their graphs

The Brownian continuum tree was extensively studied in the 90s as a universal random metric space. One construction obtains the continuum tree by a change of metric from an excursion function (or continuous circle mapping) on $[0,1]$. This change of metric can be applied to all excursion functions, and generally to continuous circle mappings. In 2008, Picard proved that the dimension theory of the tree is connected to its associated contour function: the upper box dimension of the continuum tree coincides with the variation index of the contour function. In this article we give a short and direct proof of Picard's theorem through the study of packings. We develop related and equivalent notions of variations and variation indices and study their basic properties. Finally, we link the dimension theory of the tree with the dimension theory of the graph of its contour function.