  Multi-LiDAR systems have been prevalently applied in modern autonomous
vehicles to render a broad view of the environments. The rapid development of
5G wireless technologies has brought a breakthrough for current cellular
vehicle-to-everything (C-V2X) applications. Therefore, a novel localization and
perception system in which multiple LiDARs are mounted around cities for
autonomous vehicles has been proposed. However, the existing calibration
methods require specific hard-to-move markers, ego-motion, or good initial
values given by users. In this paper, we present a novel approach that enables
automatic multi-LiDAR calibration using two poles stickered with
retro-reflective tape. This method does not depend on prior environmental
information, initial values of the extrinsic parameters, or movable platforms
like a car. We analyze the LiDAR-pole model, verify the feasibility of the
algorithm through simulation data, and present a simple method to measure the
calibration errors w.r.t the ground truth. Experimental results demonstrate
that our approach gains better flexibility and higher accuracy when compared
with the state-of-the-art approach.
