We consider two different variational models of transport networks, the
so-called branched transport problem and the urban planning problem. Based on a
novel relation to Mumford-Shah image inpainting and techniques developed in
that field, we show for a two-dimensional situation that both highly non-convex
network optimization tasks can be transformed into a convex variational
problem, which may be very useful from analytical and numerical perspectives.
As applications of the convex formulation, we use it to perform numerical
simulations (to our knowledge this is the first numerical treatment of urban
planning), and we prove the lower bound of an energy scaling law which helps
better understand optimal networks and their minimal energies