  Direct communication between humans and autonomous underwater vehicles (AUVs)
is a relatively underexplored area in human-robot interaction (HRI) research,
although many tasks (\eg surveillance, inspection, and search-and-rescue)
require close diver-robot collaboration. Many core functionalities in this
domain are in need of further study to improve robotic capabilities for ease of
interaction. One of these is the challenge of autonomous robots approaching and
positioning themselves relative to divers to initiate and facilitate
interactions. Suboptimal AUV positioning can lead to poor quality interaction
and lead to excessive cognitive and physical load for divers. In this paper, we
introduce a novel method for AUVs to autonomously navigate and achieve
diver-relative positioning to begin interaction. Our method is based only on
monocular vision, requires no global localization, and is computationally
efficient. We present our algorithm along with an implementation of said
algorithm on board both a simulated and physical AUV, performing extensive
evaluations in the form of closed-water tests in a controlled pool. Analysis of
our results show that the proposed monocular vision-based algorithm performs
reliably and efficiently operating entirely on-board the AUV.
