For the Dutch railway network, ProRail has commissioned a set of aerial images shot from a helicopter at a height of roughly 190 m, which is ridiculously high-res and available for viewing here: https://twiav.nl/nl/luchtfoto_prorail.php

You can clearly make out individual paving stones or even the catenary wire, so the resolution must be somewhere in the 1 or 2 cm range.