Real-time on-board obstacle avoidance for UAVs based on embedded stereo vision

In order to improve usability and safety, modern unmanned aerial vehicles (UAVs) are equipped with sensors to monitor the environment, such as laser-scanners and cameras. One important aspect in this monitoring process is to detect obstacles in the flight path in order to avoid collisions. Since a large number of consumer UAVs suffer from tight weight and power constraints, our work focuses on obstacle avoidance based on a lightweight stereo camera setup. We use disparity maps, which are computed from the camera images, to locate obstacles and to automatically steer the UAV around them. For disparity map computation we optimize the well-known semi-global matching (SGM) approach for the deployment on an embedded FPGA. The disparity maps are then converted into simpler representations, the so called U-/V-Maps, which are used for obstacle detection. Obstacle avoidance is based on a reactive approach which finds the shortest path around the obstacles as soon as they have a critical distance to the UAV. One of the fundamental goals of our work was the reduction of development costs by closing the gap between application development and hardware optimization. Hence, we aimed at using high-level synthesis (HLS) for porting our algorithms, which are written in C/C++, to the embedded FPGA. We evaluated our implementation of the disparity estimation on the KITTI Stereo 2015 benchmark. The integrity of the overall realtime reactive obstacle avoidance algorithm has been evaluated by using Hardware-in-the-Loop testing in conjunction with two flight simulators.Comment: Accepted in the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Scienc

Cyclists' choice of lateral position and feeling of safety between tram tracks, sharrows and parked cars

Cycling is good for the environment, healthy and affordable [1 ]. However, these benefits are offset by the risk of being involved in traffic crashes [1], with infrastructure characteristics like tram tracks or parked cars increasing aforementioned risk [2, 3]. Bicycle crashes with tram tracks can occur when cyclists turn onto streets with tram tracks or cross them for other reasons, such as avoiding parked cars on the side (oftentimes related to sudden maneuvers to avoid collisions with the door of a parked car being opened) [4]. Such collisions, referred to as dooring crashes, account for a significant proportion of bicycle crashes [3]. Nevertheless, the majority of cyclists ride in the so-called dooring zone, which is the area next to parked cars where dooring crashes can occur. If the cyclists' lateral distance to parked cars is large enough, the risk of being involved in a dooring crash can be eliminated [2]. Cyclists' position on the road can be influenced by descriptive norms which reflect a typical or normal behavior: If many other cyclists ride within the dooring zone, then the descriptive norm in this situation is to ride in the dooring zone [5]. People may also ride in the dooring zone because they are convinced that important people around them would approve of this behavior (injunctive norm), e.g. because it is communicated verbally. Apart from influencing cyclists' choice of position through norms, installing bicycle lanes with buffer zones to keep cyclists out of the dooring zone would be a solution. However, particularly in urban areas, a lack of space can make this impossible. Additionally, if tram tracks ran on the road, it is not always practical to mark bicycle lanes or protective lanes, especially when there is little space to the right of the outer tram track. In connection with frequent bicycle crashes roads with tram tracks, it is discussed whether cyclists might particularly often ride within the dooring zone there as not to have to cross the track.s [3, 6]. In those cases where marking of bicycle lanes or protective lan.es is not feasible due to width or tram track constraints, bicycle pictograms, so-called sharrows, can be marked in the middle of the lane as a measure aimed at encouraging cyclists to choose a position outside of the dooring rone and to increase their perceived safety, another factor influencing the positional choice [2]. To date, a joint experimental variation of the presence of tram tracks, parked cars, and sharrows with the aim of investigating cyclists' position on the road and their feeling of safety has not yet t.aken place. Two online studies were carried out to address this research gap, with cyclists being asked to indicate their perceived safety and their preferred position on the road based on images of a traffic situation in which the presence of tram tracks, parked cars and sharrows was varied. [From: Introduction

CROSS-DB: a feature-extended multidimensional data model for statistical and scientific databases

Statistical and scientific computing applications exhibit characteristics that are fundamentally different from classical database system application domains. The CROSS-DB data model presented in this paper is optimized for use in such applications by providing advanced data modelling methods and application-oriented query facilities, thus providing a framework for optimized data management procedures. CROSS-DB (which stands for Classification-oriented, Redundancy-based Optimization of Statistical and Scientific DataBases) is based on a multidimensional data view. The model differs from other approaches by o~ering two complementary rnechanisrnsfor structuring qualifying information, classification and feature description. Using these mechanisms results in a normalized, low-dimensional database schema which ensures both, modelling uniqueness and understandability while providing enhanced modelling flexibility

Absorptive Effects and Classical Black Hole Scattering

We describe an approach to incorporating the physical effects of the absorption of energy by the event horizon of black holes in the scattering amplitudes based post-Minkowskian, point-particle effective description. Absorptive dynamics are incorporated in a model-independent way by coupling the usual point-particle description to an invisible sector of gapless internal degrees-of-freedom. The leading order dynamics of this sector are encoded in the low-energy expansion of a spectral density function obtained by matching an absorption cross section in the ultraviolet description. This information is then recycled using the scattering amplitudes based Kosower-Maybee-O'Connell in-in formalism to calculate the leading absorptive contribution to the impulse and change in rest mass of a Schwarzschild black hole scattering with a second compact body sourcing a massless scalar, electromagnetic or gravitational field. The results obtained are in complete agreement with previous worldline Schwinger-Keldysh calculations and provide an alternative on-shell scattering amplitudes approach to incorporating horizon absorption effects in the gravitational two-body problem.Comment: 36 page

Plant surface wax affects parasitoid's response to host footprints

The plant surface is the substrate upon which herbivorous insects and natural enemies meet and thus represents the stage for interactions between the three trophic levels. Plant surfaces are covered by an epicuticular wax layer which is highly variable depending on species, cultivar or plant part. Differences in wax chemistry may modulate ecological interactions. We explored whether caterpillars of Spodoptera frugiperda, when walking over a plant surface, leave a chemical trail (kairomones) that can be detected by the parasitoid Cotesia marginiventris. Chemistry and micromorphology of cuticular waxes of two barley eceriferum wax mutants (cer-za.126, cer-yp.949) and wild type cv. Bonus (wt) were assessed. The plants were then used to investigate potential surface effects on the detectability of caterpillar kairomones. Here we provide evidence that C. marginiventris responds to chemical footprints of its host. Parasitoids were able to detect the kairomone on wild type plants and on both cer mutants but the response to cer-yp.949 (reduced wax, high aldehyde fraction) was less pronounced. Experiments with caterpillar-treated wt and mutant leaves offered simultaneously, confirmed this observation: no difference in wasp response was found when wt was tested against cer-za.126 (reduced wax, wt-like chemical composition) but wt was significantly more attractive than cer-yp.949. This demonstrates for the first time that the wax layer can modulate the detectability of host kairomones

Requirements for an Inductive Voltage Adder as Driver for a Kicker Magnet with Short Circuit Termination

At CERN pulse generators based on Thyratron switches and SF6 gas filled pulse forming lines, used for driving kicker magnets, are to be replaced with semiconductor technology. Preliminary investigations show the inductive voltage adder is suitable as a pulse generator for this application. To increase the magnetic field without raising the system voltage, a short-circuit termination is often applied to a kicker magnet. Because of the electrical length of a transmission line magnet, wave propagation needs to be considered. To allow for the wavefront reflected from the short-circuit termination back to the generator, a novel approach for an inductive adder architecture has been investigated. It is based on a modified generator interface, circulating the current back into the load, until the stored energy is absorbed at the end of the pulse. This approach allows for a smaller magnetic core size compared to a conventional design with a matched load. Moreover, it enables more energy-efficient operation involving smaller storage capacitors. This paper summarizes the conceptual design features and furthermore gives an overview of the parameter space for possible applications at CERN