The dynamics of systems of interacting agents is determined by the structure of their coupling
network. The knowledge of the latter is therefore highly desirable, for instance to develop efficient
control schemes, to accurately predict the dynamics or to better understand inter-agent processes.
In many important and interesting situations, the network structure is not known, however, and
previous investigations have shown how it may be inferred from complete measurement time series,
on each and every agent. These methods implicitly presuppose that, even though the network is not
known, all its nodes are. A major shortcoming of theirs is that they cannot provide any reliable
information, not even on partial network structures, as soon as some agents are unobservable.
Here, we construct a novel method that determines network structures even when not all agents
are measurable. We establish analytically and illustrate numerically that velocity signal correlators
encode not only direct couplings, but also geodesic distances in the coupling network, within the
subset of measurable agents. When dynamical data are accessible for all agents, our method is
furthermore algorithmically more efficient than the traditional ones, because it does not rely on
matrix inversion.