1,595 research outputs found
Meeting in a Polygon by Anonymous Oblivious Robots
The Meeting problem for searchers in a polygon (possibly with
holes) consists in making the searchers move within , according to a
distributed algorithm, in such a way that at least two of them eventually come
to see each other, regardless of their initial positions. The polygon is
initially unknown to the searchers, and its edges obstruct both movement and
vision. Depending on the shape of , we minimize the number of searchers
for which the Meeting problem is solvable. Specifically, if has a
rotational symmetry of order (where corresponds to no
rotational symmetry), we prove that searchers are sufficient, and
the bound is tight. Furthermore, we give an improved algorithm that optimally
solves the Meeting problem with searchers in all polygons whose
barycenter is not in a hole (which includes the polygons with no holes). Our
algorithms can be implemented in a variety of standard models of mobile robots
operating in Look-Compute-Move cycles. For instance, if the searchers have
memory but are anonymous, asynchronous, and have no agreement on a coordinate
system or a notion of clockwise direction, then our algorithms work even if the
initial memory contents of the searchers are arbitrary and possibly misleading.
Moreover, oblivious searchers can execute our algorithms as well, encoding
information by carefully positioning themselves within the polygon. This code
is computable with basic arithmetic operations, and each searcher can
geometrically construct its own destination point at each cycle using only a
compass. We stress that such memoryless searchers may be located anywhere in
the polygon when the execution begins, and hence the information they initially
encode is arbitrary. Our algorithms use a self-stabilizing map construction
subroutine which is of independent interest.Comment: 37 pages, 9 figure
Positional Encoding by Robots with Non-Rigid Movements
Consider a set of autonomous computational entities, called \emph{robots},
operating inside a polygonal enclosure (possibly with holes), that have to
perform some collaborative tasks. The boundary of the polygon obstructs both
visibility and mobility of a robot. Since the polygon is initially unknown to
the robots, the natural approach is to first explore and construct a map of the
polygon. For this, the robots need an unlimited amount of persistent memory to
store the snapshots taken from different points inside the polygon. However, it
has been shown by Di Luna et al. [DISC 2017] that map construction can be done
even by oblivious robots by employing a positional encoding strategy where a
robot carefully positions itself inside the polygon to encode information in
the binary representation of its distance from the closest polygon vertex. Of
course, to execute this strategy, it is crucial for the robots to make accurate
movements. In this paper, we address the question whether this technique can be
implemented even when the movements of the robots are unpredictable in the
sense that the robot can be stopped by the adversary during its movement before
reaching its destination. However, there exists a constant ,
unknown to the robot, such that the robot can always reach its destination if
it has to move by no more than amount. This model is known in
literature as \emph{non-rigid} movement. We give a partial answer to the
question in the affirmative by presenting a map construction algorithm for
robots with non-rigid movement, but having bits of persistent memory and
ability to make circular moves
Meeting in a Polygon by Anonymous Oblivious Robots
The Meeting problem for k>=2 searchers in a polygon P (possibly with holes) consists in making the searchers move within P, according to a distributed algorithm, in such a way that at least two of them eventually come to see each other, regardless of their initial positions. The polygon is initially unknown to the searchers, and its edges obstruct both movement and vision. Depending on the shape of P, we minimize the number of searchers k for which the Meeting problem is solvable. Specifically, if P has a rotational symmetry of order sigma (where sigma=1 corresponds to no rotational symmetry), we prove that k=sigma+1 searchers are sufficient, and the bound is tight. Furthermore, we give an improved algorithm that optimally solves the Meeting problem with k=2 searchers in all polygons whose barycenter is not in a hole (which includes the polygons with no holes). Our algorithms can be implemented in a variety of standard models of mobile robots operating in Look-Compute-Move cycles. For instance, if the searchers have memory but are anonymous, asynchronous, and have no agreement on a coordinate system or a notion of clockwise direction, then our algorithms work even if the initial memory contents of the searchers are arbitrary and possibly misleading. Moreover, oblivious searchers can execute our algorithms as well, encoding information by carefully positioning themselves within the polygon. This code is computable with basic arithmetic operations (provided that the coordinates of the polygon\u27s vertices are algebraic real numbers in some global coordinate system), and each searcher can geometrically construct its own destination point at each cycle using only a compass. We stress that such memoryless searchers may be located anywhere in the polygon when the execution begins, and hence the information they initially encode is arbitrary. Our algorithms use a self-stabilizing map construction subroutine which is of independent interest
Adaptive Path Planning for Depth Constrained Bathymetric Mapping with an Autonomous Surface Vessel
This paper describes the design, implementation and testing of a suite of
algorithms to enable depth constrained autonomous bathymetric (underwater
topography) mapping by an Autonomous Surface Vessel (ASV). Given a target depth
and a bounding polygon, the ASV will find and follow the intersection of the
bounding polygon and the depth contour as modeled online with a Gaussian
Process (GP). This intersection, once mapped, will then be used as a boundary
within which a path will be planned for coverage to build a map of the
Bathymetry. Methods for sequential updates to GP's are described allowing
online fitting, prediction and hyper-parameter optimisation on a small embedded
PC. New algorithms are introduced for the partitioning of convex polygons to
allow efficient path planning for coverage. These algorithms are tested both in
simulation and in the field with a small twin hull differential thrust vessel
built for the task.Comment: 21 pages, 9 Figures, 1 Table. Submitted to The Journal of Field
Robotic
Vision-Based Localization Algorithm Based on Landmark Matching, Triangulation, Reconstruction, and Comparison
Many generic position-estimation algorithms are vulnerable to ambiguity introduced by nonunique landmarks. Also, the available high-dimensional image data is not fully used when these techniques are extended to vision-based localization. This paper presents the landmark matching, triangulation, reconstruction, and comparison (LTRC) global localization algorithm, which is reasonably immune to ambiguous landmark matches. It extracts natural landmarks for the (rough) matching stage before generating the list of possible position estimates through triangulation. Reconstruction and comparison then rank the possible estimates. The LTRC algorithm has been implemented using an interpreted language, onto a robot equipped with a panoramic vision system. Empirical data shows remarkable improvement in accuracy when compared with the established random sample consensus method. LTRC is also robust against inaccurate map data
Origami constraints on the initial-conditions arrangement of dark-matter caustics and streams
In a cold-dark-matter universe, cosmological structure formation proceeds in
rough analogy to origami folding. Dark matter occupies a three-dimensional
'sheet' of free- fall observers, non-intersecting in six-dimensional
velocity-position phase space. At early times, the sheet was flat like an
origami sheet, i.e. velocities were essentially zero, but as time passes, the
sheet folds up to form cosmic structure. The present paper further illustrates
this analogy, and clarifies a Lagrangian definition of caustics and streams:
caustics are two-dimensional surfaces in this initial sheet along which it
folds, tessellating Lagrangian space into a set of three-dimensional regions,
i.e. streams. The main scientific result of the paper is that streams may be
colored by only two colors, with no two neighbouring streams (i.e. streams on
either side of a caustic surface) colored the same. The two colors correspond
to positive and negative parities of local Lagrangian volumes. This is a severe
restriction on the connectivity and therefore arrangement of streams in
Lagrangian space, since arbitrarily many colors can be necessary to color a
general arrangement of three-dimensional regions. This stream two-colorability
has consequences from graph theory, which we explain. Then, using N-body
simulations, we test how these caustics correspond in Lagrangian space to the
boundaries of haloes, filaments and walls. We also test how well outer caustics
correspond to a Zel'dovich-approximation prediction.Comment: Clarifications and slight changes to match version accepted to MNRAS.
9 pages, 5 figure
Analysis of Elephant Movement in Sub-Saharan Africa: Ecological, Climatic, and Conservation Perspectives
The interaction between elephants and their environment has profound
implications for both ecology and conservation strategies. This study presents
an analytical approach to decipher the intricate patterns of elephant movement
in Sub-Saharan Africa, concentrating on key ecological drivers such as seasonal
variations and rainfall patterns. Despite the complexities surrounding these
influential factors, our analysis provides a holistic view of elephant
migratory behavior in the context of the dynamic African landscape. Our
comprehensive approach enables us to predict the potential impact of these
ecological determinants on elephant migration, a critical step in establishing
informed conservation strategies. This projection is particularly crucial given
the impacts of global climate change on seasonal and rainfall patterns, which
could substantially influence elephant movements in the future. The findings of
our work aim to not only advance the understanding of movement ecology but also
foster a sustainable coexistence of humans and elephants in Sub-Saharan Africa.
By predicting potential elephant routes, our work can inform strategies to
minimize human-elephant conflict, effectively manage land use, and enhance
anti-poaching efforts. This research underscores the importance of integrating
movement ecology and climatic variables for effective wildlife management and
conservation planning.Comment: 11 pages, 17 figures, Accepted in ACM SIGCAS SIGCHI Conference on
Computing and Sustainable Societies (COMPASS 2023
Intelligent Ground Vehicle Competition
The Intelligent Ground Vehicle Competition (IGVC) draws teams from various universities to compete in the annual autonomous vehicle challenge at the Oakland University campus. To compete, a vehicle must be fully autonomous and can navigate a course designated by various obstacles and painted white lines. Some design challenges are motor control, navigation, environment sensing and safety. A complex navigation system will utilize several tools including a high-precision differential GPS. The vehicle’s surroundings will be mapped using a combination of Light Detection and Ranging (LiDAR) and computer-vision enabled imaging. To comply with IGVC rules, the vehicle must also follow several safety requirements such as physical and wireless emergency stop, safety lighting, and the ability to assume manual control. By fulfilling these design challenges, the design team is seeking to compete in the 2017 Intelligent Ground Vehicle Competition
Developing Android Mobile Map Application with standard navigation tools for pedestrians
Advanced features of modern mobile devices have made it possible to develop and use maps and map based applications for navigation purposes. Since most mobile map applications nowadays are developed for motor vehicles, there is a demand for portable pedestrian navigation applications. In this thesis the Android mobile map application with standard navigation tools for pedestrian navigation was developed, as a platform for facilitating the Lund Challenge location based demonstrator of the HaptiMap project. The pivotal aim of the Lund Challenge demonstrator is to make the sights of Lund city more accessible. The mobile phone application is being designed as a touristic, historical location based game which will also assist tourists to navigate themselves in the city. To enable exploration of historical and current sites of Lund the demonstrator should contain basic components of exploring and way finding. Prior to the development the OpenStreetMap (OSM) road network data and Swedish National Road Database (NVDB) were introduced. The main advantage of using the OSM data over the NVDB dataset is the completeness of the OSM data in terms of pedestrian paths. The datasets were imported to PostgreSQL spatially extended PostGIS database, where different routing algorithms provided by pgRouting were used for routing calculations. As the Lund Challenge demonstrator is intended not only for general users but also for visually impaired users, the problem of user navigation in the parks and open areas were also discussed and the feasibility study was performed. The limitation of the developed application was the problem of the user navigation in the parks and open areas. It is therefore necessary to upgrade the road database with possible path in the open areas and parks in order to implement this application.Advanced features of modern devices have made it possible to develop and use maps and map-based applications for navigation purposes. Since most mobile map applications are currently developed for motor vehicles, there is a demand for portable pedestrian navigation applications. In this thesis, a mobile map application was developed with standard navigation tools for pedestrians, which can be used with mobile phones running Android Operating System. The application will be used as a platform for facilitating the Lund Challenge location based demonstrator. Lund Challenge location based demonstrator is designed to make historical and actual maps of Lund more accessible and is a part of the HaptiMap project. This project aims to create maps and develop location-based services for all users, including elderly and visually impaired. The goal of the Lund Challenge location based demonstrator (also known as The Lund Time Machine) is to minimize the efforts of pedestrians, especially tourists, with finding interesting sites around the city. Initially, it is being designed as a historical location based game which will assist tourists to navigate themselves around the city. In order to further explore historical and current sites, the Lund Challenge should be enhanced with the basic features of exploration and navigation included in this thesis. The road network data was chosen from two available sources: 1) data from OpenStreetMap (OSM) project which provides free geographic data, and 2) The Swedish National Road Database (NVDB) authorized by the Swedish government, which includes all Swedish road network and selected cycle paths. For this thesis, analysis was performed on the datasets using different shortest path algorithms for routing calculations. A primary advantage of using OSM over NVDB is the completeness of data relating to pedestrian paths. As a result, the determination was made that the OSM option was more appropriate for the purpose of this thesis. Since the Lund Challenge location based demonstrator is intended for both general and visually impaired users, the problem of user navigation in parks and open areas was also discussed and a feasibility study was performed. This study revealed a limitation in the application with user navigation in parks and open areas. To resolve this, it is necessary to upgrade the road network with all possible pedestrian paths for parks and open areas
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