Abstract. This paper presents an underwater laser scanning system and GNSS based trajectory estimation system for scanning from a surface vessle in shallow water. The system has an above-the-water and an underwater component. Above-the-water two low-cost multiband GNSS receivers with an antenna baseline of one meter are used for RTK positioning with heading. The full 6-DOF is estimated by fusing the satellite navigation data with a MEMS-based INS. The 3D data is captured in water using a structured light scanner consisting of a low-light underwater camera and a green cross line laser projector. We describe the development of the system and employed hardware components. We show results of scanning a large test object in a water tank acquired by from a tripod with a motorized yaw axis. Additionally, we demonstrate first results of mobile mapping from a floating platform. We evaluate the performance of the system by measuring the 6-DOF trajectory with an external optical tracking system. Additionally, we assess the quality of the created point cloud using reference objects placed in the scene.
In view of the sinking level of consensus and the allegedly growing 'presidentialization' of politics in Switzerland, this paper asks whether this process can be explained by the 'mediatization of politics', enforced by the commercialization of the media. Taking a comparative approach in analyzing news coverage about executive and parliamentary elections from 1960 to 2011 in three different media types, it shows an increasing focus on executive elections, triggered not only by increasing political conflict but also by commercialized 'media logic'. Attention to the executive is highest in the commercialized tabloid paper and lowest in the less commercialized quality paper, which only much later starts to focus on these elections. Contested executive elections have become attractive for commercialized media to focus on prominent figures and dramatize conflicts. This news reporting about politics arguably gives incentives for political actors to contest executive elections, thus intensifying the transformation of the political system.
In this work we look at 3D acquisition of semi-submerged structures with a triangulation based underwater laser scanning system. The motivation is that we want to simultaneously capture data above and below water to create a consistent model without any gaps. The employed structured light scanner consist of a machine vision camera and a green line laser. In order to reconstruct precise surface models of the object it is necessary to model and correct for the refraction of the laser line and camera rays at the water-air boundary.We derive a geometric model for the refraction at the air-water interface and propose a method for correcting the scans. Furthermore, we show how the water surface is directly estimated from sensor data. The approach is verified using scans captured with an industrial manipulator to achieve reproducable scanner trajectories with different incident angles. We show that the proposed method is effective for refractive correction and that it can be applied directly to the raw sensor data without requiring any external markers or targets.
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