New Applications of the Nearest-Neighbor Chain Algorithm

The nearest-neighbor chain algorithm was proposed in the eighties as a way to speed up certain hierarchical clustering algorithms. In the first part of the dissertation, we show that its application is not limited to clustering. We apply it to a variety of geometric and combinatorial problems. In each case, we show that the nearest-neighbor chain algorithm finds the same solution as a preexistent greedy algorithm, but often with an improved runtime. We obtain speedups over greedy algorithms for Euclidean TSP, Steiner TSP in planar graphs, straight skeletons, a geometric coverage problem, and three stable matching models. In the second part, we study the stable-matching Voronoi diagram, a type of plane partition which combines properties of stable matchings and Voronoi diagrams. We propose political redistricting as an application. We also show that it is impossible to compute this diagram in an algebraic model of computation, and give three algorithmic approaches to overcome this obstacle. One of them is based on the nearest-neighbor chain algorithm, linking the two parts together

Terrain Representation And Reasoning In Computer Generated Forces : A Survey Of Computer Generated Forces Systems And How They Represent And Reason About Terrain

Report on a survey of computer systems used to produce realistic or intelligent behavior by autonomous entities in simulation systems. In particular, it is concerned with the data structures used by computer generated forces systems to represent terrain and the algorithmic approaches used by those systems to reason about terrain

Time-differentiated distribution of service parts and repair materials: an investigation of service time, area partitions, and cost relations

Motivation: Manufacturers in sectors like Information Technology (IT), Automotive and Aerospace have increasingly become focused on providing after sales services. One of the forms of after sales services is to provide service parts (or spare parts) to customers within different contracted time windows. Commonly offered by large scale IT sector companies, such services are facilitated by Service Parts Logistics (SPL) systems through a network of parts stocking facilities. The number of stocking facilities in a distribution network affects the service responsiveness and service costs related to inventory, transportation and facility set-up. Higher responsiveness can be attained through increasing the number of facilities in a distribution network, which, in turn, usually increases inventory cost. Generally, studies assume that shorter service time windows result in higher costs, but there is a lack of exploration regarding how reductions in service time limits and changes in the fractions of demand for different time-based service types impact on various service related costs. Service area partitioning (or zoning) is another related issue which is unexplored in general facility location literature when considering multiple service time (or distance) constraints and both inventory and transportation costs. This study is mainly motivated by SPL systems of IT equipment manufacturers that support the provision of service parts at customer sites under different and short service time commitments in a large geographical area. The study is of a generic nature and generates insights that can be relevant for any case where the service responses are provided within different short time windows and involve the provision (or consumption) of some stocks (e.g. emergency infrastructure repairs). Aim and methodology: The aim of this work is to investigate relationships between time-based service levels, service costs and service zones/areas under a hierarchical organization and a non-hierarchical organization of service facilities. The hierarchical organization has variable capabilities to meet different time-based requirements, while the non-hierarchical organization has a uniform capability to meet the toughest requirement for the entire customer base. The investigation is mainly done through analytical, simulation and optimization modelling with the view of producing answers that provide a general understanding and practical insights rather than producing situation specific optimization models. Empirical case studies are also conducted to complement the quantitative modelling work so that the research is not divorced from the reality. The case studies point towards the motivation for the modelling study and its relevance to some of the real-world systems, and provide a broader understanding of the issues being researched. The case studies involve two multinational ICT equipment manufacturers and service provides, and a government agency responsible for providing highway emergency services in England. Key findings: The results from the modelling experiments show that under the non-hierarchical setup, where all facilities provide the full range of service-times in their respective vicinities, inventory and transportation costs are insensitive to the fractions of demand for different time-based service types. However, with an inventory sharing mechanism under the non-hierarchical setup, the increase in the proportion of demand for the service within the longer time window can increase the service availability level while also increasing the average travelling. On the other hand, under the hierarchical setup, which provides a higher level of centralization when there is demand for the service in the longer time window, inventory and transportation costs react to the proportions of demand for different time-based service types. The hierarchical setup results in higher transportation cost compared to the non-hierarchical setup, and, interestingly, does not necessarily lower the inventory level, especially when the overall demand rate is very low. The simulation of the inventory sharing mechanism under the hierarchical setup shows that, in several cases, inventory sharing can not only increase the service availability level, but can also reduce transportation cost. The analysis based on the optimization models shows that there can be cases where it is more cost effective to serve all demand, regardless of the required service time, in a similar fashion through a non-hierarchical setup. The results also show that the demand fractions for different time-based service types, and inventory and transportation costs can significantly impact on the optimum organization of service zone. There can be distinct optimum patterns of service zones depending on whether the inventory cost or the transportation cost dominates

Automated generation of geometrically-precise and semantically-informed virtual geographic environnements populated with spatially-reasoning agents

La Géo-Simulation Multi-Agent (GSMA) est un paradigme de modélisation et de simulation de phénomènes dynamiques dans une variété de domaines d'applications tels que le domaine du transport, le domaine des télécommunications, le domaine environnemental, etc. La GSMA est utilisée pour étudier et analyser des phénomènes qui mettent en jeu un grand nombre d'acteurs simulés (implémentés par des agents) qui évoluent et interagissent avec une représentation explicite de l'espace qu'on appelle Environnement Géographique Virtuel (EGV). Afin de pouvoir interagir avec son environnement géographique qui peut être dynamique, complexe et étendu (à grande échelle), un agent doit d'abord disposer d'une représentation détaillée de ce dernier. Les EGV classiques se limitent généralement à une représentation géométrique du monde réel laissant de côté les informations topologiques et sémantiques qui le caractérisent. Ceci a pour conséquence d'une part de produire des simulations multi-agents non plausibles, et, d'autre part, de réduire les capacités de raisonnement spatial des agents situés. La planification de chemin est un exemple typique de raisonnement spatial dont un agent pourrait avoir besoin dans une GSMA. Les approches classiques de planification de chemin se limitent à calculer un chemin qui lie deux positions situées dans l'espace et qui soit sans obstacle. Ces approches ne prennent pas en compte les caractéristiques de l'environnement (topologiques et sémantiques), ni celles des agents (types et capacités). Les agents situés ne possèdent donc pas de moyens leur permettant d'acquérir les connaissances nécessaires sur l'environnement virtuel pour pouvoir prendre une décision spatiale informée. Pour répondre à ces limites, nous proposons une nouvelle approche pour générer automatiquement des Environnements Géographiques Virtuels Informés (EGVI) en utilisant les données fournies par les Systèmes d'Information Géographique (SIG) enrichies par des informations sémantiques pour produire des GSMA précises et plus réalistes. De plus, nous présentons un algorithme de planification hiérarchique de chemin qui tire avantage de la description enrichie et optimisée de l'EGVI pour fournir aux agents un chemin qui tient compte à la fois des caractéristiques de leur environnement virtuel et de leurs types et capacités. Finalement, nous proposons une approche pour la gestion des connaissances sur l'environnement virtuel qui vise à supporter la prise de décision informée et le raisonnement spatial des agents situés

Geofencing Motion Planning for Unmanned Aerial Vehicles Using an Anticipatory Range Control Algorithm

© 2023 The Author(s). Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/This paper presents a range control approach for implementing hard geofencing for unmanned air vehicles (UAVs), and especially remotely piloted versions (RPVs), via a proposed anticipatory range calculator. The approach employs turning circle intersection tests that anticipate the fence perimeter on approach. This ensures the vehicle turns before penetrating the geofence and remains inside the allowable operational airspace by accounting for the vehicles’ turning dynamics. Allowance is made for general geozone shapes and locations, including those located at the problematic poles and meridians where nonlinear angle mapping is dealt with, concave geozones, narrow corners with acute internal angles, and transient turn dynamics. The algorithm is shown to prevent any excursions using a high-fidelity simulation of a small remotely piloted vehicle. The algorithm relies on a single tuning parameter which can be determined from the closed-loop rise time in the aircraft’s roll command tracking.Peer reviewe

Self-organizing Network Optimization via Placement of Additional Nodes

Das Hauptforschungsgebiet des Graduiertenkollegs "International Graduate School on Mobile Communication" (GS Mobicom) der Technischen Universität Ilmenau ist die Kommunikation in Katastrophenszenarien. Wegen eines Desasters oder einer Katastrophe können die terrestrischen Elementen der Infrastruktur eines Kommunikationsnetzwerks beschädigt oder komplett zerstört werden. Dennoch spielen verfügbare Kommunikationsnetze eine sehr wichtige Rolle während der Rettungsmaßnahmen, besonders für die Koordinierung der Rettungstruppen und für die Kommunikation zwischen ihren Mitgliedern. Ein solcher Service kann durch ein mobiles Ad-Hoc-Netzwerk (MANET) zur Verfügung gestellt werden. Ein typisches Problem der MANETs ist Netzwerkpartitionierung, welche zur Isolation von verschiedenen Knotengruppen führt. Eine mögliche Lösung dieses Problems ist die Positionierung von zusätzlichen Knoten, welche die Verbindung zwischen den isolierten Partitionen wiederherstellen können. Hauptziele dieser Arbeit sind die Recherche und die Entwicklung von Algorithmen und Methoden zur Positionierung der zusätzlichen Knoten. Der Fokus der Recherche liegt auf Untersuchung der verteilten Algorithmen zur Bestimmung der Positionen für die zusätzlichen Knoten. Die verteilten Algorithmen benutzen nur die Information, welche in einer lokalen Umgebung eines Knotens verfügbar ist, und dadurch entsteht ein selbstorganisierendes System. Jedoch wird das gesamte Netzwerk hier vor allem innerhalb eines ganz speziellen Szenarios - Katastrophenszenario - betrachtet. In einer solchen Situation kann die Information über die Topologie des zu reparierenden Netzwerks im Voraus erfasst werden und soll, natürlich, für die Wiederherstellung mitbenutzt werden. Dank der eventuell verfügbaren zusätzlichen Information können die Positionen für die zusätzlichen Knoten genauer ermittelt werden. Die Arbeit umfasst eine Beschreibung, Implementierungsdetails und eine Evaluierung eines selbstorganisierendes Systems, welche die Netzwerkwiederherstellung in beiden Szenarien ermöglicht.The main research area of the International Graduate School on Mobile Communication (GS Mobicom) at Ilmenau University of Technology is communication in disaster scenarios. Due to a disaster or an accident, the network infrastructure can be damaged or even completely destroyed. However, available communication networks play a vital role during the rescue activities especially for the coordination of the rescue teams and for the communication between their members. Such a communication service can be provided by a Mobile Ad-Hoc Network (MANET). One of the typical problems of a MANET is network partitioning, when separate groups of nodes become isolated from each other. One possible solution for this problem is the placement of additional nodes in order to reconstruct the communication links between isolated network partitions. The primary goal of this work is the research and development of algorithms and methods for the placement of additional nodes. The focus of this research lies on the investigation of distributed algorithms for the placement of additional nodes, which use only the information from the nodes’ local environment and thus form a self-organizing system. However, during the usage specifics of the system in a disaster scenario, global information about the topology of the network to be recovered can be known or collected in advance. In this case, it is of course reasonable to use this information in order to calculate the placement positions more precisely. The work provides the description, the implementation details and the evaluation of a self-organizing system which is able to recover from network partitioning in both situations

Time-differentiated distribution of service parts and repair materials: an investigation of service time, area partitions, and cost relations

Motivation: Manufacturers in sectors like Information Technology (IT), Automotive and Aerospace have increasingly become focused on providing after sales services. One of the forms of after sales services is to provide service parts (or spare parts) to customers within different contracted time windows. Commonly offered by large scale IT sector companies, such services are facilitated by Service Parts Logistics (SPL) systems through a network of parts stocking facilities. The number of stocking facilities in a distribution network affects the service responsiveness and service costs related to inventory, transportation and facility set-up. Higher responsiveness can be attained through increasing the number of facilities in a distribution network, which, in turn, usually increases inventory cost. Generally, studies assume that shorter service time windows result in higher costs, but there is a lack of exploration regarding how reductions in service time limits and changes in the fractions of demand for different time-based service types impact on various service related costs. Service area partitioning (or zoning) is another related issue which is unexplored in general facility location literature when considering multiple service time (or distance) constraints and both inventory and transportation costs. This study is mainly motivated by SPL systems of IT equipment manufacturers that support the provision of service parts at customer sites under different and short service time commitments in a large geographical area. The study is of a generic nature and generates insights that can be relevant for any case where the service responses are provided within different short time windows and involve the provision (or consumption) of some stocks (e.g. emergency infrastructure repairs). Aim and methodology: The aim of this work is to investigate relationships between time-based service levels, service costs and service zones/areas under a hierarchical organization and a non-hierarchical organization of service facilities. The hierarchical organization has variable capabilities to meet different time-based requirements, while the non-hierarchical organization has a uniform capability to meet the toughest requirement for the entire customer base. The investigation is mainly done through analytical, simulation and optimization modelling with the view of producing answers that provide a general understanding and practical insights rather than producing situation specific optimization models. Empirical case studies are also conducted to complement the quantitative modelling work so that the research is not divorced from the reality. The case studies point towards the motivation for the modelling study and its relevance to some of the real-world systems, and provide a broader understanding of the issues being researched. The case studies involve two multinational ICT equipment manufacturers and service provides, and a government agency responsible for providing highway emergency services in England. Key findings: The results from the modelling experiments show that under the non-hierarchical setup, where all facilities provide the full range of service-times in their respective vicinities, inventory and transportation costs are insensitive to the fractions of demand for different time-based service types. However, with an inventory sharing mechanism under the non-hierarchical setup, the increase in the proportion of demand for the service within the longer time window can increase the service availability level while also increasing the average travelling. On the other hand, under the hierarchical setup, which provides a higher level of centralization when there is demand for the service in the longer time window, inventory and transportation costs react to the proportions of demand for different time-based service types. The hierarchical setup results in higher transportation cost compared to the non-hierarchical setup, and, interestingly, does not necessarily lower the inventory level, especially when the overall demand rate is very low. The simulation of the inventory sharing mechanism under the hierarchical setup shows that, in several cases, inventory sharing can not only increase the service availability level, but can also reduce transportation cost. The analysis based on the optimization models shows that there can be cases where it is more cost effective to serve all demand, regardless of the required service time, in a similar fashion through a non-hierarchical setup. The results also show that the demand fractions for different time-based service types, and inventory and transportation costs can significantly impact on the optimum organization of service zone. There can be distinct optimum patterns of service zones depending on whether the inventory cost or the transportation cost dominates

A generic triangle-based data structure of the complete set of higher order Voronoi diagrams for emergency management

We introduce a generic Delaunay triangle-based data structure for geoinformation processing in disaster and emergency management. The data structure supports the complete set of higher order Voronoi diagrams (order-k) Voronoi diagrams, ordered order-k Voronoi diagrams, and kth nearest Voronoi diagrams for all (k). It provides useful and insightful information for what-if nearest queries, what-if neighboring queries, what-if zoning queries, what-if facility locating queries and what-if routing queries to handle various scenarios in the four stages of emergency management (mitigation, preparedness, response and recovery). We also demonstrate how the complete set of higher order Voronoi diagrams can be used for each phase of emergency management in diverse geoinformatics environments