This paper deals with the calibration of a visual system, consisting of RGB cameras and 3D Light Detection And Ranging (LiDAR) sensors. Registering two separate point clouds coming from different modalities is always challenging. We propose a novel and accurate calibration method using simple cardboard boxes with known sizes. Our approach is principally based on the detection of box planes in LiDAR point clouds, thus it can calibrate different Li-DAR equipments. Moreover, camera-LiDAR calibration is also possible with minimal manual intervention. The proposed algorithm is validated and compared to state-ofthe-art techniques both on synthesized data and real-world measurements taken by a visual system consisting of LiDAR sensors and RGB cameras.

As autonomous driving attracts more and more attention these days, the algorithms and sensors used for machine perception become popular in research, as well. This paper investigates the extrinsic calibration of two frequently-applied sensors: the camera and Light Detection and Ranging (LiDAR). The calibration can be done with the help of ordinary boxes. It contains an iterative refinement step, which is proven to converge to the box in the LiDAR point cloud, and can be used for system calibration containing multiple LiDARs and cameras. For that purpose, a bundle adjustment-like minimization is also presented. The accuracy of the method is evaluated on both synthetic and real-world data, outperforming the state-of-the-art techniques. The method is general in the sense that it is both LiDAR and camera-type independent, and only the intrinsic camera parameters have to be known. Finally, a method for determining the 2D bounding box of the car chassis from LiDAR point clouds is also presented in order to determine the car body border with respect to the calibrated sensors.

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Polyurethanes, manufactured from aromatic and aliphatic isocyanates (1), [1] are an important class of high-performance materials. Aliphatic polyisocyanates are the preferred building blocks for coatings and most are based on hexamethylene diisocyanate (HDI). For the majority of applications, oligomers of HDI with significantly lower vapor pressure than that of the monomer are required. These oligomers are predominantly cyclo-oligomers, such as uretdiones 2,[2] isocyanurates 3, [3] and iminooxadiazinediones 4, [4] which can be prepared by catalytic cyclo-oligomerization of monomeric isocyanates. [5] Although phosphines, including tri-n-butylphosphine (5), have been used commercially as catalysts for more than 20 years, [6] no information is available on the mechanism of the reaction. Based on the reactivity of nucleophiles towards heterocumulenes, [7] the reaction may start by the nucleophilic attack of the phosphine on the carbonyl group of the isocyanate to form a zwitterionic intermediate A, followed by reaction with another isocyanate moiety to result in a second zwitterionic intermediate B (Scheme 1). Although an intramolecular nucleophilic attack by the À O(RN)À ion on the carbonyl group of B could lead to the formation of 2 and 5, the addition of another isocyanate moiety could result in the formation of zwitterionic intermediates C 1 and