32 research outputs found

    The link between true larvae and parasitic forms within Isopoda – insights from the fossil record

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    Isopoda is a species-rich ingroup of Eucrustacea (crustaceans and insects), whose representatives live in a variety of habitats from the deep sea to arid terrestrial landscapes. Isopoda is very diverse regarding the life styles which are present in its species. There are herbivorous and detritivorous species as well as predators and scavengers. Parasitism, as an interaction between animals where one animal exploits resources from the other to it’s disadvantage, is far from being a fringe phenomenon inside Isopoda – a large proportion of species in Isopoda are either parasites or micro-predators (also referred to as temporary parasites). Parasitic forms (in the wider sense, including micro-predators) of Isopoda can be found in a few ingroups, which are generally thought to be closely related or to form a monophyletic group. Among the parasitic forms there are many species whose development includes a strong ecological and morphological differentiation between the immatures and the adults (larval development). Despite the ecological importance in modern ecosystems, the fossil record of parasitic forms of Isopoda is rather sparse. The aim of this study was to recognise and thoroughly document potentially parasitic forms of Isopoda in the fossil record, using modern imaging techniques. By interpreting the systematic positions of the extinct species, the fossil forms could be compared with closely related extant forms for which there are observations of their behaviour in their natural environment. The goal was also to recognise potentially immature forms, which could provide insights into the evolution of developmental patterns within Isopoda, especially with respect to the parasitic forms in which there seems to be a stronger tendency for differentiation between adults and their offspring. Fossils have the potential to yield combinations of characters that are not present in extant species and are thereby important to reconstruct the evolution of characters. Fossils of such value were explicitly searched for. Furthermore, the fossils inspected in the studies of this dissertation should be used to provide a temporal context to the evolution of parasitism and larval development within Isopoda. Two well-preserved fossils of presumably non-parasitic forms within the group Cymothoida (in which there are also parasitic forms) from fossilised mid-Cretaceous resin were studied (study I). One of them was interpreted as an immature, which resembles the other, larger, specimen, which is assumed to be of a later developmental stage, in most aspects of the body morphology – except for the absence of a well developed leg on the posterior-most walking leg, which absence in immatures is an apomorphy of the group Mancoidea, which comprises Isopoda. This represents, together with a recently published fossil of the same site, the oldest record of an immature specimen in Isopoda. Multiple minute fossils of the group Epicaridea (parasites of crustaceans) from two different mid- and Late Cretaceous amber localities (studies I and III) were studied. They represent the oldest body fossils of the group Epicaridea, which has a rich record of fossil traces which its representatives left on their host (growth responses by the host) while feeding on them. Based on the available morphological features, the fossils were identified as either larvae (of the cryptoniscium stage) or paedomorphic adult males. Their presence in the fossil record suggests that the complex life cycle that is found in extant species of Epicaridea was already present in the Cretaceous. An assemblage of multiple strongly compressed fossils from the Eocene of the Czech Republic was documented (study IV). The specimens were identified as being either close relatives to or representatives of group Cymothoidae (mostly parasites of fishes in the extant fauna). This marks the first and therefore oldest reliable record of this lineage in the fossil record. The assemblage contains specimens of different body sizes. Together with differences in the overall body shape this indicates the presence of immature stages. Fossils of Urda, an extinct, potentially non-monophyletic group with a unique combination of characters, were analysed (study V). The fossils are interpreted as the closest so far known relatives of the extant group Gnathiidae (temporary parasites of fishes), with which representatives they share a number of apomorphic characters; a convincing apomorphy for Urda could not be found. The fossils, for which there is no indication that they represent remains of immatures, are very similar in many aspects to immature forms of Gnathiidae, in contrast to which they, however, lack the paedomorphic absence of legs on one segment of the trunk. The occurrence of some fossils of Urda on fossils of fishes suggests a syn-vivo interaction, such as parasitism or commensalism. Fossils of Urda provide important information about the character evolution towards modern, fish-parasites of the group Gnathiidae. The evolution of larvae within Isopoda seems to be deeply interlinked with the evolution of parasitism. The fossil record yields specimens with a larval development that date back to the mid-Cretaceous. These specimens simultaneously represent the oldest fossils which can be identified as belonging to extant groups in which all species have a parasitic life style. Close relatives of extant parasites date back even further, to the Lower Jurassic. Overall, despite still being patchy, the fossil record of Isopoda provides unique insights into the evolution of parasitic forms as well as into the differentiation between adults and immature forms

    Vision Sensors and Edge Detection

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    Vision Sensors and Edge Detection book reflects a selection of recent developments within the area of vision sensors and edge detection. There are two sections in this book. The first section presents vision sensors with applications to panoramic vision sensors, wireless vision sensors, and automated vision sensor inspection, and the second one shows image processing techniques, such as, image measurements, image transformations, filtering, and parallel computing

    Global Shipping Container Monitoring Using Machine Learning with Multi-Sensor Hubs and Catadioptric Imaging

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    We describe a framework for global shipping container monitoring using machine learning with multi-sensor hubs and infrared catadioptric imaging. A wireless mesh radio satellite tag architecture provides connectivity anywhere in the world which is a significant improvement to legacy methods. We discuss the design and testing of a low-cost long-wave infrared catadioptric imaging device and multi-sensor hub combination as an intelligent edge computing system that, when equipped with physics-based machine learning algorithms, can interpret the scene inside a shipping container to make efficient use of expensive communications bandwidth. The histogram of oriented gradients and T-channel (HOG+) feature as introduced for human detection on low-resolution infrared catadioptric images is shown to be effective for various mirror shapes designed to give wide volume coverage with controlled distortion. Initial results for through-metal communication with ultrasonic guided waves show promise using the Dynamic Wavelet Fingerprint Technique (DWFT) to identify Lamb waves in a complicated ultrasonic signal

    Omnidirectional Stereo Vision for Autonomous Vehicles

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    Environment perception with cameras is an important requirement for many applications for autonomous vehicles and robots. This work presents a stereoscopic omnidirectional camera system for autonomous vehicles which resolves the problem of a limited field of view and provides a 360° panoramic view of the environment. We present a new projection model for these cameras and show that the camera setup overcomes major drawbacks of traditional perspective cameras in many applications

    Enhancing 3D Visual Odometry with Single-Camera Stereo Omnidirectional Systems

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    We explore low-cost solutions for efficiently improving the 3D pose estimation problem of a single camera moving in an unfamiliar environment. The visual odometry (VO) task -- as it is called when using computer vision to estimate egomotion -- is of particular interest to mobile robots as well as humans with visual impairments. The payload capacity of small robots like micro-aerial vehicles (drones) requires the use of portable perception equipment, which is constrained by size, weight, energy consumption, and processing power. Using a single camera as the passive sensor for the VO task satisfies these requirements, and it motivates the proposed solutions presented in this thesis. To deliver the portability goal with a single off-the-shelf camera, we have taken two approaches: The first one, and the most extensively studied here, revolves around an unorthodox camera-mirrors configuration (catadioptrics) achieving a stereo omnidirectional system (SOS). The second approach relies on expanding the visual features from the scene into higher dimensionalities to track the pose of a conventional camera in a photogrammetric fashion. The first goal has many interdependent challenges, which we address as part of this thesis: SOS design, projection model, adequate calibration procedure, and application to VO. We show several practical advantages for the single-camera SOS due to its complete 360-degree stereo views, that other conventional 3D sensors lack due to their limited field of view. Since our omnidirectional stereo (omnistereo) views are captured by a single camera, a truly instantaneous pair of panoramic images is possible for 3D perception tasks. Finally, we address the VO problem as a direct multichannel tracking approach, which increases the pose estimation accuracy of the baseline method (i.e., using only grayscale or color information) under the photometric error minimization as the heart of the “direct” tracking algorithm. Currently, this solution has been tested on standard monocular cameras, but it could also be applied to an SOS. We believe the challenges that we attempted to solve have not been considered previously with the level of detail needed for successfully performing VO with a single camera as the ultimate goal in both real-life and simulated scenes

    Catadioptric stereo-vision system using a spherical mirror

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    Abstract In the computer vision field, the reconstruction of target surfaces is usually achieved by using 3D optical scanners assembled integrating digital cameras and light emitters. However, these solutions are limited by the low field of view, which requires multiple acquisition from different views to reconstruct complex free-form geometries. The combination of mirrors and lenses (catadioptric systems) can be adopted to overcome this issue. In this work, a stereo catadioptric optical scanner has been developed by assembling two digital cameras, a spherical mirror and a multimedia white light projector. The adopted configuration defines a non-single viewpoint system, thus a non-central catadioptric camera model has been developed. An analytical solution to compute the projection of a scene point onto the image plane (forward projection) and vice-versa (backward projection) is presented. The proposed optical setup allows omnidirectional stereo vision thus allowing the reconstruction of target surfaces with a single acquisition. Preliminary results, obtained measuring a hollow specimen, demonstrated the effectiveness of the described approach

    Refractive Structure-From-Motion Through a Flat Refractive Interface

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    Recovering 3D scene geometry from underwater images involves the Refractive Structure-from-Motion (RSfM) problem, where the image distortions caused by light refraction at the interface between different propagation media invalidates the single view point assumption. Direct use of the pinhole camera model in RSfM leads to inaccurate camera pose estimation and consequently drift. RSfM methods have been thoroughly studied for the case of a thick glass interface that assumes two refractive interfaces between the camera and the viewed scene. On the other hand, when the camera lens is in direct contact with the water, there is only one refractive interface. By explicitly considering a refractive interface, we develop a succinct derivation of the refractive fundamental matrix in the form of the generalised epipolar constraint for an axial camera. We use the refractive fundamental matrix to refine initial pose estimates obtained by assuming the pinhole model. This strategy allows us to robustly estimate underwater camera poses, where other methods suffer from poor noise-sensitivity. We also formulate a new four view constraint enforcing camera pose consistency along a video which leads us to a novel RSfM framework. For validation we use synthetic data to show the numerical properties of our method and we provide results on real data to demonstrate performance within laboratory settings and for applications in endoscopy

    Implementación de unwarping de videos omnidireccionales en la plataforma Jetson TK1

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    El unwarping es un método utilizado para transformar imágenes omnidireccionales en imágenes panorámicas, el cual es empleado en aplicaciones tales como seguridad, visión robótica, geolocalización, etc. El procesamiento de imágenes omnidireccionales de alta resolución y su aplicación en dispositivos móviles se ve limitado por el costo computacional y costo energético. Para ello, se plantea como herramienta principal utilizar la plataforma Jetson TK1, la cual es un system on chip (SoC) creada por Nvidia que se caracteriza por su alto rendimiento computacional y bajo costo energético al tener incorporado 192 núcleos en su procesador gráfico. En el presente trabajo se desarrolla e implementa un algoritmo para realizar el unwarping de videos omnidireccionales en la plataforma Jetson TK1, la cual permite optimizar las transferencias y procesamientos de datos realizados en su GPU. El algoritmo es implementado en el entorno de programación MATLAB y CUDA para evaluar error por cálculo y eficiencia computacional. Asimismo, se compara en rendimiento computacional con el método PMPA, el cual es una alternativa escrita en lenguaje C computacionalmente eficiente en comparación a otros métodos presentados en el Capítulo 1. Los resultados de la comparación muestran que la implementación propuesta es 1.35 a 8.12 veces más rápida que el algoritmo PMPA para los tipos de interpolación utilizados (interpolación vecino más cercano e interpolación bilineal). El orden que sigue la tesis es el siguiente: En el primer capítulo se realizara un breve estado del arte sobre los métodos para realizar el unwarping de imágenes omnidireccionales. En el segundo capítulo se cubren los aspectos teóricos del modelo de programación CUDA necesarios para el diseño del algoritmo paralelo. En el tercer capítulo se describe de forma detallada el método propuesto y su diseño paralelo. Por ´ultimo, en el cuarto capítulo se presentan los resultados computacionales seguido de las conclusiones y recomendaciones. Finalmente, cabe señalar que el trabajo de investigación realizado fue presentado en el GPU Technology Conference 2015.Tesi
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