Dijkstra Search Research Articles

Research on hull curved plate surface flattening method based on Dijkstra search and compass intersection solving

Abstract The change of the surface curvature during the line heating forming process of ship outer plates changes the spatial position of frame lines on the surface, which makes it challenging to locate the position of frame lines during the digital plate-forming inspection. It is necessary to establish the mapping between the frame line data of complex surface shape and the corresponding data in the two-dimensional flattening state with the help of surface flattening algorithms, so as to obtain the spatial position of the frame line data of outer plates in the actual forming state. A Dijkstra-compass intersection-solving algorithm is proposed to achieve surface flattening of ship outer plates. Firstly, the point cloud data of the outer plate shape surface is interpolated and fitted by NURBS to obtain the surface data of the outer plate. Then, the Dijkstra search algorithm is used to find the geodesic, and the frame line curvature is calculated according to the triangular similarity law. Finally, the geodesic line and the middle frame line are expanded, and the surface flattening data is obtained by further expanding the mesh points. This method is used to flatten the cylindrical and circular table surfaces, and the flattening error is less than 3mm compared with theoretical values. The test results show that the proposed method can effectively flatten the three-dimensional surface of the ship’s outer plates, and the deployment accuracy meets the actual use requirements.

A Unified Framework Integrating Decision Making and Trajectory Planning Based on Spatio-Temporal Voxels for Highway Autonomous Driving

Intelligent decision making and efficient trajectory planning are closely related in autonomous driving technology, especially in highway environment full of dynamic interactive traffic participants. This work integrates them into a unified hierarchical framework with long-term behavior planning (LTBP) and short-term dynamic planning (STDP) running in two parallel threads with different horizon, consequently forming a closed-loop maneuver and trajectory planning system that can react to the dynamic environment effectively and efficiently. In LTBP, a novel voxel structure and the ‘voxel expansion’ algorithm are proposed for the generation of driving corridors in 3D configuration, which involves the prediction states of surrounding vehicles. By using Dijkstra search, the maneuver with minimal cost is determined in form of voxel sequences, then a quadratic programming (QP) problem is constructed for solving the optimal trajectory. And in STDP, another small-scaled QP problem is performed to track or adjust the reference trajectory from LTBP in response to the dynamic obstacles. Meanwhile, a Responsibility-Sensitive Safety (RSS) Checker keeps running at high frequency for real-time feedback to ensure security. Experiments on real data collected in different highway scenarios demonstrate the effectiveness and efficiency of our work.

Improving Time-Dependent Contraction Hierarchies

Computing time-optimal shortest paths, in road networks, is one of the most popular applications of Artificial Intelligence. This problem is tricky to solve because road congestion affects travel times. The state-of-the-art in this area is an algorithm called Time-dependent Contraction Hierarchies (TCH). Although fast and optimal, TCH still suffers from two main drawbacks: (1) the usual query process uses bi-directional Dijkstra search to find the shortest path, which can be time-consuming; and (2) the TCH is constructed w.r.t. the entire time domain T, which complicates the search process for queries q that start and finish in a smaller time period Tq ⊂ T. In this work, we improve TCH by making use of time-independent heuristics, which speed up optimal search, and by computing TCHs for different subsets of the time domain, which further reduces the size of the search space. We give a full description of these methods and discuss their optimality-preserving characteristics. We report significant query time improvements against a baseline implementation of TCH.

Forward Search in Contraction Hierarchies

Contraction hierarchies are graph-based data structure developed to speed up shortest path search in road networks. Built during an offline pre-processing step, contraction hierarchies are always paired with an online query algorithm which is a variation on bi-directional Dijkstra search. Though effective and highly popular this combination can sometimes be difficult to extend, for example in order to leverage goal-directed heuristics or other forward-driven pruning techniques. In this paper we deconstruct the bi-directional query algorithm of contraction hierarchies and derive a new algorithmic schema which is compatible with standard uni-directional or bi-directional search. We then develop a variety of new uni-directional query algorithms to find optimal paths in contraction hierarchies. These are based on the combination of A* search and Geometric Containers, a well known and successful edge-pruning technique. Empirical results show that our approach can improve search times by an order of magnitude vs bi-directional Dijkstra, albeit at the cost of additional memory and pre-processing time.

Robotic Path Planning Based on a Triangular Mesh Map

Aiming at the problem of robot path planning in complex maps, an algorithm of robot path planning based on triangular grid graph is proposed. Firstly, a weighted undirected loop graph and a feasible domain of nodes are obtained by discretizing the triangular mesh map. Next, the Dijkstra search algorithm is applied to find the feasible shortest path from an initial to a final configuration. Finally, The Douglas-Peucker algorithm is applied to remove duplicate and redundant nodes in the feasible path, and the waypoint are extracted. The final path is a curve that is obtained by connecting the several extracted waypoint. The proposed algorithm is tested for various maps. Compared with probabilistic roadmap method, the experimental results show that the proposed method can overcome the shortcomings of the random sampling method. Furthermore, the experimental result of triangular mesh map method used in two labyrinth maps show that the triangular mesh map method can solve the robot path planning problem in complex map very well, and it is an excellent algorithm for robot path planning.

Optimal Integrated Model for Feeder Transit Route Design and Frequency-Setting Problem with Stop Selection

This study proposed a mathematical model for designing a feeder transit service for improving the service quality and accessibility of transportation hubs (such as airport and rail station). The proposed model featured an integrated framework, which simultaneously guided passengers to reach their nearest stops to get on and off the bus, designed routes to transport passengers from these selected pick-up stops to the transportation hubs, and calculated their departure frequencies. In particular, the maximum walking distance, the upper and lower limits of route frequencies, and the load factor rate of each route were fully accounted for in this study. The main objective of the proposed model was to simultaneously minimize the total walking, riding time, and waiting time of all passengers. As this study explored an NP-hard problem, a two-stage genetic algorithm combining the Dijkstra search method was further developed to yield metaoptimal solutions to the model within an acceptable time. Finally, a test instance in Chongqing City, China, demonstrated that the proposed model was an effective tool to generate a pedestrian, route, and operation plan; it reduced the total travel time, compared with the traditional model.

Improving the Combination of JPS and Geometric Containers

The JPS family of grid-based pathfinding algorithms can be improved with preprocessing methods such as Geometric Containers. However, such enhancements require a Dijkstra search for every node in the grid and the space and time costs of all this additional computation can be prohibitive. In this work we consider an alternative approach where we run Dijkstra only from every node where a jump point is located. We also compute and store geometric containers only for those outgoing edges which are consistent with the diagonal-first ordering in JPS. Since the number of jump points on a grid is usually much smaller than the total number of grid cells, we can save up to orders of magnitude of time and space. In addition to improving preprocessing overheads, we also present a partial expansion strategy which can improve the performance of online search by reducing the total number of operations on the open list.

An energy-efficient path planning algorithm for unmanned surface vehicles

The sea current state affects the energy consumption of Unmanned Surface Vehicles (USVs) significantly and the path planning approach plays an important role in determining how long the USV can travel. To improve the endurance of the USV, an energy efficient path planning approach for computing feasible paths for USVs that takes the energy consumption into account based on sea current data is proposed. The approach also ensures that the USV remains at a user-configurable safety distance away from all islands and coastlines. In the proposed approach, Voronoi diagram, Visibility graph, Dijkstra's search and energy consumption function are combined, which allows USVs to avoid obstacles while at the same time using minimum amount of energy. The Voronoi-Visibility (VV) energy-efficient path and the corresponding shortest path were simulated and compared for ten missions in Singapore Strait and five missions for islands off the coast of Croatia. Impact of parameters such as mission time, the USV speed and sea current state on the results were analysed. It is shown that the proposed VV algorithm improves the quality of the Voronoi energy efficient path while keeping the same level of computational efficiency as that of the Voronoi energy efficient path planning algorithm.

Efficient Path Planning Algorithms for Unmanned Surface Vehicle

Abstract: The C-Enduro Unmanned Surface Vehicle (USV) is designed to operate at sea for extended periods of time (up to 3 months). To increase the endurance capability of the USV, an energy efficient path planning algorithm is developed. The proposed path planning algorithm integrates the Voronoi diagram, Visibility algorithm, Dijkstra search algorithm and takes also into account the sea current data. Ten USV simulated mission scenarios at different time of day and start/end points were analysed. The proposed approach shows that the amount of energy saved can be up to 21%. Moreover, the proposed algorithm can be used to calculate a collision free and energy efficient path to keep the USV safe and improve the USV capability. The safety distance between the USV and the coastline can also be configured by the user.

High-Throughput and Area-Efficient MIMO Symbol Detection Based on Modified Dijkstra's Search

The multiple-input-multiple-output (MIMO) technique is being actively adopted in recent wireless communication standards to enhance data rate. Though channel capacity is increased by adopting multiple spatial streams, the computational complexity needed to eliminate the interference hinders the implementation of a practical system. In this paper, we propose a modified Dijkstra's algorithm and a precalculation technique to improve the throughput by allowing overlapped processing. For the maximum-likelihood (ML) detection, in addition, we propose a simple approximation of L2-norm calculation to reduce the computational complexity without degrading the error performance noticeably. A MIMO symbol detector based on the proposed algorithm is implemented in a 0.18- μm CMOS process, targeting 4 × 4 16-QAM. It occupies about 0.5 mm2 with 25.1 K equivalent gates and shows a throughput of over 300 Mb/s.

Iterative MIMO sphere decoding throughput guarantees under realistic channel conditions

Block-based early termination has been proposed for depth-first based MIMO sphere decoders (SD) in order to provide throughput guarantees. We show in this letter that such termination incurs, even under simple tree and norm choices, significant overhead in the required number of iterations under realistic channel conditions due to the depth-first search's highly variable complexity (number of iterations to achieve a target performance). We propose the use of a constrained version of Dijkstra's metric-first search which exhibits indistinguishable performance while avoiding the impractical memory requirements of Dijkstra's search. We show that for a 4×4 64-subcarrier OFDM system, the proposed alternative achieves ~2x decrease in complexity as compared to the depth-first SD with block early termination for the same throughput guarantee.

The visibility–Voronoi complex and its applications

We introduce a new type of diagram called the VV ( c ) -diagram (the visibility–Voronoi diagram for clearance c), which is a hybrid between the visibility graph and the Voronoi diagram of polygons in the plane. It evolves from the visibility graph to the Voronoi diagram as the parameter c grows from 0 to ∞. This diagram can be used for planning natural-looking paths for a robot translating amidst polygonal obstacles in the plane. A natural-looking path is short, smooth, and keeps—where possible—an amount of clearance c from the obstacles. The VV ( c ) -diagram contains such paths. We also propose an algorithm that is capable of preprocessing a scene of configuration-space polygonal obstacles and constructs a data structure called the VV-complex. The VV-complex can be used to efficiently plan motion paths for any start and goal configuration and any clearance value c, without having to explicitly construct the VV ( c ) -diagram for that c-value. The preprocessing time is O ( n 2 log n ) , where n is the total number of obstacle vertices, and the data structure can be queried directly for any c-value by merely performing a Dijkstra search. We have implemented a Cgal-based software package for computing the VV ( c ) -diagram in an exact manner for a given clearance value and used it to plan natural-looking paths in various applications.

2P1-G03 多様な動作計画のためのデュアルダイキストラ法

2P1-G03 多様な動作計画のためのデュアルダイキストラ法

Shortest path planning on topographical maps

This paper introduces a new algorithm for quickly answering repetitive least-cost queries between pairs of points on the Earth's surface as represented by digital topographical maps. The algorithm uses a three-step process; preprocessing, geometrically modified Dijkstra search, and postprocessing. The preprocessing step computes and saves highly valuable global information that describes the underlying geometry of the terrain. The search step solves shortest path queries using a modified Dijkstra algorithm that takes advantage of the preprocessed information to "jump" quickly across flat terrain and decide whether a path should go over or through a high-cost region. The final step is a path improvement process that straightens and globally improves the path. Our algorithm partitions the search space into free regions and obstacle regions. However, unlike other algorithms using this approach, our algorithm keeps the option of passing through an obstacle region.

A New Curriculum for Ethology & Student Skills in the Netherlands: Part 2: Innovation & Implementation Activities

Research Article| October 01 1997 A New Curriculum for Ethology & Student Skills in the Netherlands: Part 2: Innovation & Implementation Activities Bram J. Jansen, Bram J. Jansen Search for other works by this author on: This Site PubMed Google Scholar Maurits J. Dijkstra, Maurits J. Dijkstra Search for other works by this author on: This Site PubMed Google Scholar Alex Bloem Alex Bloem Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1997) 59 (8): 488–490. https://doi.org/10.2307/4450363 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Bram J. Jansen, Maurits J. Dijkstra, Alex Bloem; A New Curriculum for Ethology & Student Skills in the Netherlands: Part 2: Innovation & Implementation Activities. The American Biology Teacher 1 October 1997; 59 (8): 488–490. doi: https://doi.org/10.2307/4450363 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright 1997 The National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.

Religious Determinants of Academic Attainment in the Netherlands

Previous articleNext article No AccessReligious Determinants of Academic Attainment in the NetherlandsAnnebert Dijkstra and Jules L. PescharAnnebert Dijkstra Search for more articles by this author and Jules L. Peschar Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Comparative Education Review Volume 40, Number 1Feb., 1996Special Issue on Religion Sponsored by the Comparative and International Education Society Article DOIhttps://doi.org/10.1086/447355 Views: 13Total views on this site Citations: 14Citations are reported from Crossref Copyright 1996 The Comparative and International Education SocietyPDF download Crossref reports the following articles citing this article:Giliberto Capano, Anthony R. Zito, Federico Toth, Jeremy Rayner The Education Policy Sector, (Aug 2022): 75–113.https://doi.org/10.1007/978-3-031-07457-8_3Geeti Sharma, Sahil Gupta, Aastha Sawhney, Sanjay Rastogi Examining the influence of demographic marginalisation on performance of the students in higher education, Journal of Public Affairs 21, no.33 (Aug 2020).https://doi.org/10.1002/pa.2267William Jeynes The Removal of Character Education from the Public Schools and America’s Moral Decline Since 1963, (Sep 2011): 25–47.https://doi.org/10.1007/978-94-007-2387-0_2Geert Driessen, Michael S. Merry The effects of integration and generation of immigrants on language and numeracy achievement, Educational Studies 37, no.55 (Jan 2011): 581–592.https://doi.org/10.1080/03055698.2010.539762M. Mooney Religion, College Grades, and Satisfaction among Students at Elite Colleges and Universities, Sociology of Religion 71, no.22 (Jun 2010): 197–215.https://doi.org/10.1093/socrel/srq035Siegwart Lindenberg James Coleman, (Dec 2007): 90–121.https://doi.org/10.1002/9780470999912.ch5Christopher J. Schreck, Melissa W. Burek, Jason Clark-Miller He Sends Rain Upon the Wicked, Journal of Interpersonal Violence 22, no.77 (Jul 2016): 872–893.https://doi.org/10.1177/0886260507301233William H. Jeynes The Relatonship Between Urban Students Attending Religious Revival Services and Academic and Social Outcomes, Education and Urban Society 38, no.11 (Nov 2005): 3–20.https://doi.org/10.1177/0013124505280028 Michael S. Merry Social Exclusion of Muslim Youth in Flemish‐ and French‐Speaking Belgian Schools Merry, Comparative Education Review 49, no.11 (Jul 2015): 1–23.https://doi.org/10.1086/426158Sam Chul Park The Impact of Internal and External Factors on Christian School Culture in South Korea: A Document Content Analysis, Journal of Christian Education os-46, no.11 (Dec 2016): 43–58.https://doi.org/10.1177/002196570304600106William H. Jeynes The Effects Of Black And Hispanic 12th Graders Living In Intact Families And Being Religious On Their Academic Achievement, Urban Education 38, no.11 (Aug 2016): 35–57.https://doi.org/10.1177/0042085902238685William H. Jeynes The Effects of the Religious Commitment of Twelfth Graders Living in Non-Intact Families on Their Academic Achievement, Marriage & Family Review 35, no.1-21-2 (Jan 2003): 77–97.https://doi.org/10.1300/J002v35n01_06Roelande H. Hofman, W. H. Adriaan Hofman, Henk Guldemond School governance, culture, and student achievement, International Journal of Leadership in Education 5, no.33 (Sep 2002): 249–272.https://doi.org/10.1080/136031202760217009William H. Jeynes The Effects of Religious Commitment on the Academic Achievement of Black and Hispanic Children, Urban Education 34, no.44 (Aug 2016): 458–479.https://doi.org/10.1177/0042085999344003