  This paper details an application which yields significant improvements to
the adeptness of place recognition with Frequency-Modulated Continuous-Wave
radar - a commercially promising sensor poised for exploitation in mobile
autonomy. We show how a rotationally-invariant metric embedding for radar scans
can be integrated into sequence-based trajectory matching systems typically
applied to videos taken by visual sensors. Due to the complete horizontal field
of view inherent to the radar scan formation process, we show how this
off-the-shelf sequence-based trajectory matching system can be manipulated to
detect place matches when the vehicle is travelling down a previously visited
stretch of road in the opposite direction. We demonstrate the efficacy of the
approach on 26 km of challenging urban driving taken from the largest
radar-focused urban autonomy dataset released to date -- showing a boost of 30%
in recall at high levels of precision over a nearest neighbour approach.
