3DRadar2ThermalCalib: Accurate Extrinsic Calibration between a 3D mmWave Radar and a Thermal Camera Using a Spherical-Trihedral

Both 3D mmWave Radar (3D:
$x, y, z$
) and thermal camera are robust in harsh environments. Fusing them is beneficial for V2X road side units and unmanned vehicles to operate in all-weather conditions. To fuse the two sensors, accurate extrinsic calibration is indispensable. However, limited literatures can be found, since 3D radar is pushed into the market just for a short period. Most research are focused on 2D radar (2D:
$x, y$
) and rgb camera calibration. Recently, one research is proposed for 3D radar and rgb camera, but it requires continuous movement of the sensors to perform hand-eye calibration. It is impractical for the sensors mounted to the road side in V2X, where the sensors are non-movable. To solve the problems, 3DRadar2ThermalCalib is proposed. 1) A novel calibration target, a spherical-trihedral, is introduced. We use the sphere center as the common feature. It can be directly detected by both sensors. 2) We propose the methods to automatically detect the sphere center from both sensors. 3) The optimal extrinsic parameter is obtained by minimizing the re-projection error. Both quantitative and qualitative analysis in real environments demonstrate the method is accurate. The re-projection error can reach 1.88 pixels.