  We present a robust multi-robot convoying approach that relies on visual
detection of the leading agent, thus enabling target following in unstructured
3-D environments. Our method is based on the idea of tracking-by-detection,
which interleaves efficient model-based object detection with temporal
filtering of image-based bounding box estimation. This approach has the
important advantage of mitigating tracking drift (i.e. drifting away from the
target object), which is a common symptom of model-free trackers and is
detrimental to sustained convoying in practice. To illustrate our solution, we
collected extensive footage of an underwater robot in ocean settings, and
hand-annotated its location in each frame. Based on this dataset, we present an
empirical comparison of multiple tracker variants, including the use of several
convolutional neural networks, both with and without recurrent connections, as
well as frequency-based model-free trackers. We also demonstrate the
practicality of this tracking-by-detection strategy in real-world scenarios by
successfully controlling a legged underwater robot in five degrees of freedom
to follow another robot's independent motion.
