Analysis of error functions for the iterative closest point algorithm

Dans les dernières années, beaucoup de progrès a été fait dans le domaine des voitures autonomes. Plusieurs grandes compagnies travaillent à créer un véhicule robuste et sûr. Pour réaliser cette tâche, ces voitures utilisent un lidar pour la localisation et pour la cartographie. Iterative Closest Point (ICP)est un algorithme de recalage de points utilisé pour la cartographie basé sur les lidars. Ce mémoire explore des approches pour améliorer le minimisateur d’erreur d’ICP. La première approche est une analyse en profondeur des filtres à données aberrantes. Quatorze des filtres les plus communs (incluant les M-estimateurs) ont été testés dans différents types d’environnement, pour un total de plus de 2 millions de recalages. Les résultats expérimentaux montrent que la plupart des filtres ont des performances similaires, s’ils sont correctement paramétrés. Néanmoins, les filtres comme Var.Trim., Cauchy et Cauchy MAD sont plus stables à travers tous les types environnements testés. La deuxième approche explore les possibilités de la cartographie à grande échelle à l’aide de lidar dans la forêt boréale. La cartographie avec un lidar est souvent basée sur des techniques de Simultaneous Localization and Mapping (SLAM) utilisant un graphe de poses, celui-ci fusionne ensemble ICP, les positions Global Navigation Satellite System (GNSS) et les mesures de l’Inertial Measurement Unit (IMU). Nous proposons une approche alternative qui fusionne ses capteurs directement dans l’étape de minimisation d’ICP. Nous avons réussi à créer une carte ayant 4.1 km de tracés de motoneige et de chemins étroits. Cette carte est localement et globalement cohérente.In recent years a lot of progress has been made in the development of self-driving cars. Multiple big companies are working on creating a safe and robust autonomous vehicle . To make this task possible, theses vehicles rely on lidar sensors for localization and mapping. Iterative Closest Point (ICP) is a registration algorithm used in lidar-based mapping. This thesis explored approaches to improve the error minimization of ICP. The first approach is an in-depth analysis of outlier filters. Fourteen of the most common outlier filters (such as M-estimators) have been tested in different types of environments, for a total of more than two million registrations. The experimental results show that most outlier filters have a similar performance if they are correctly tuned. Nonetheless, filters such as Var.Trim., Cauchy, and Cauchy MAD are more stable against different environment types. The second approach explores the possibilities of large-scale lidar mapping in a boreal forest. Lidar mapping is often based on the SLAM technique relying on pose graph optimization, which fuses the ICP algorithm, GNSS positioning, and IMU measurements. To handle those sensors directly within theICP minimization process, we propose an alternative technique of embedding external constraints. We manage to create a crisp and globally consistent map of 4.1 km of snowmobile trails and narrow walkable trails. These two approaches show how ICP can be improved through the modification of a single step of the ICP’s pipeline

Estimating underwater light regime under spatially heterogeneous sea ice in the Arctic

Abstract: The vertical diffuse attenuation coefficient for downward plane irradiance (Kd ) is an apparent optical property commonly used in primary production models to propagate incident solar radiation in the water column. In open water, estimating Kd is relatively straightforward when a vertical profile of measurements of downward irradiance, Ed, is available. In the Arctic, the ice pack is characterized by a complex mosaic composed of sea ice with snow, ridges, melt ponds, and leads. Due to the resulting spatially heterogeneous light field in the top meters of the water column, it is difficult to measure at single-point locations meaningful Kd values that allow predicting average irradiance at any depth. The main objective of this work is to propose a new method to estimate average irradiance over large spatially heterogeneous area as it would be seen by drifting phytoplankton. Using both in situ data and 3D Monte Carlo numerical simulations of radiative transfer, we show that (1) the large-area average vertical profile of downward irradiance, Ed(z), under heterogeneous sea ice cover can be represented by a single-term exponential function and (2) the vertical attenuation coefficient for upward radiance (KLu), which is up to two times less influenced by a heterogeneous incident light field than Kd in the vicinity of a melt pond, can be used as a proxy to estimate Ed(z) in the water column

Zooplankton assemblages along the North American Arctic: Ecological connectivity shaped by ocean circulation and bathymetry from the Chukchi Sea to Labrador Sea

We defined mesozooplankton biogeography in the North American Arctic to elucidate drivers of biodiversity, community structure, and biomass of this key component of the Arctic marine ecosystem. A multivariate analysis identified four mesozooplankton assemblages: Arctic-oceanic, Arctic-shelf, Coastal-Hudson, and Labrador Sea. Bathymetry was a major driver of the distribution of these assemblages. In shallow waters, Cirripedia and the copepod Pseudocalanus spp. dominated the Coastal-Hudson and Arctic-shelf assemblages, which showed low species richness (19) and biomass (0.28 and 1.49 g C m-2 , respectively).The Arctic-oceanic assemblage occupied the entire North American Arctic, except for shallow breaks in the Canadian Arctic Archipelago downstream of sills blocking the Atlantic Water layer circulation below a depth of 200 m. This assemblage showed high copepod biomass (4.74 g C m-2 ) with a high share of Calanus hyperboreus, C. glacialis, and Metridia longa. In habitats below 200-m depth, C. hyperboreus represented 68% of the copepod biomass, underscoring its role as a keystone species in this ecosystem. Strong numerical representation by the borealAtlantic C. finmarchicus and Oithona atlantica stressed the strong Atlantic influence on the subarctic Labrador Sea assemblage on the northwestern Labrador Sea slope. The mixed Arctic-Atlantic composition of the Labrador Sea mesozooplankton resulted in high species richness (58) and biomass (5.73 g C m-2 ). The low abundance of Atlantic and Pacific taxa in the areas influenced by Arctic currents did not alter the Arctic status of the Arctic-oceanic, Arctic-shelf, and Coastal-Hudson assemblages.This study identifies hotspots of mesozooplankton biomass and diversity in Central Amundsen Gulf, Lancaster Sound, North Water Polynya and Baffin Bay, known for their high biological productivity and concentrations of vertebrate predators. The continental-scale zooplankton mapping furthers our understanding of the importance of bathymetry and ocean circulation for ecological connectivity in a vast and complex portion of the Arctic marine ecosystem

Mucous Membrane Pemphigoid in a Nonagenarian: A Case Report

Mucous membrane pemphigoid is a rare autoimmune blistering disease characterized by post-bullous erosion of mucous membranes. Herein, we present a case of a nonagenarian man who was referred to our department of dermatology presenting with painful erosion of the buccal mucosa. Physical examination revealed palate erosion associated with erosion of the buccal mucosa. A diagnosis of mucous membrane pemphigoid was confirmed, and the patient was successfully treated with topical corticosteroids