Editorial

2 pages, 170 KiB

Open AccessEditorial

by Faramarz F. Samavati and Troy Alderson

ISPRS Int. J. Geo-Inf. 2020, 9(6), 376; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9060376 - 08 Jun 2020

Cited by 3 | Viewed by 1717

This Special Issue is dedicated to research papers on topics related to global grid systems, from their geometric foundations to their cutting-edge applications [...] Full article

(This article belongs to the Special Issue Global Grid Systems)

Research

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17 pages, 4136 KiB

Open AccessArticle

Modelling Offset Regions around Static and Mobile Locations on a Discrete Global Grid System: An IoT Case Study

by David Bowater and Monica Wachowicz

ISPRS Int. J. Geo-Inf. 2020, 9(5), 335; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9050335 - 20 May 2020

Cited by 6 | Viewed by 2709

Abstract

With the huge volume of location-based point data being generated by Internet of Things (IoT) devices and subsequent rising interest from the Digital Earth community, a need has emerged for spatial operations that are compatible with Digital Earth frameworks, the foundation of which [...] Read more.

With the huge volume of location-based point data being generated by Internet of Things (IoT) devices and subsequent rising interest from the Digital Earth community, a need has emerged for spatial operations that are compatible with Digital Earth frameworks, the foundation of which are Discrete Global Grid Systems (DGGSs). Offsetting is a fundamental spatial operation that allows us to determine the region within a given distance of an IoT device location, which is important for visualizing or querying nearby location-based data. Thus, in this paper, we present methods of modelling an offset region around the point location of an IoT device (both static and mobile) that is quantized into a cell of a DGGS. Notably, these methods illustrate how the underlying indexing structure of a DGGS can be utilized to determine the cells in an offset region at different spatial resolutions. For a static IoT device location, we describe a single resolution approach as well as a multiresolution approach that allows us to efficiently determine the cells in an offset region at finer (or coarser) resolutions. For mobile IoT device locations, we describe methods to efficiently determine the cells in successive offset regions at fine and coarse resolutions. Lastly, we present a variety of results that demonstrate the effectiveness of the proposed methods. Full article

(This article belongs to the Special Issue Global Grid Systems)

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20 pages, 6776 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Disdyakis Triacontahedron DGGS

by John Hall, Lakin Wecker, Benjamin Ulmer and Faramarz Samavati

ISPRS Int. J. Geo-Inf. 2020, 9(5), 315; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9050315 - 08 May 2020

Cited by 16 | Viewed by 4967

Abstract

The amount of information collected about the Earth has become extremely large. With this information comes the demand for integration, processing, visualization and distribution of this data so that it can be leveraged to solve real-world problems. To address this issue, a carefully [...] Read more.

The amount of information collected about the Earth has become extremely large. With this information comes the demand for integration, processing, visualization and distribution of this data so that it can be leveraged to solve real-world problems. To address this issue, a carefully designed information structure is needed that stores all of the information about the Earth in a convenient format such that it can be easily used to solve a wide variety of problems. The idea which we explore is to create a Discrete Global Grid System (DGGS) using a Disdyakis Triacontahedron (DT) as the initial polyhedron. We have adapted a simple, closed-form, equal-area projection to reduce distortion and speed up queries. We have derived an efficient, closed-form inverse for this projection that can be used in important DGGS queries. The resulting construction is indexed using an atlas of connectivity maps. Using some simple modular arithmetic, we can then address point to cell, neighbourhood and hierarchical queries on the grid, allowing for these queries to be performed in constant time. We have evaluated the angular distortion created by our DGGS by comparing it to a traditional icosahedron DGGS using a similar projection. We demonstrate that our grid reduces angular distortion while allowing for real-time rendering of data across the globe. Full article

(This article belongs to the Special Issue Global Grid Systems)

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24 pages, 4374 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

General Method for Extending Discrete Global Grid Systems to Three Dimensions

by Benjamin Ulmer, John Hall and Faramarz Samavati

ISPRS Int. J. Geo-Inf. 2020, 9(4), 233; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9040233 - 10 Apr 2020

Cited by 7 | Viewed by 3982

Abstract

Geospatial sensors are generating increasing amounts of three-dimensional (3D) data. While Discrete Global Grid Systems (DGGS) are a useful tool for integrating geospatial data, they provide no native support for 3D data. Several different 3D global grids have been proposed; however, these approaches [...] Read more.

Geospatial sensors are generating increasing amounts of three-dimensional (3D) data. While Discrete Global Grid Systems (DGGS) are a useful tool for integrating geospatial data, they provide no native support for 3D data. Several different 3D global grids have been proposed; however, these approaches are not consistent with state-of-the-art DGGSs. In this paper, we propose a general method that can extend any DGGS to the third dimension to operate as a 3D DGGS. This extension is done carefully to ensure any valid DGGS can be supported, including all refinement factors and non-congruent refinement. We define encoding, decoding, and indexing operations in a way that splits responsibility between the surface DGGS and the 3D component, which allows for easy transference of data between the 2D and 3D versions of a DGGS. As a part of this, we use radial mapping functions that serve a similar purpose as polyhedral projection in a conventional DGGS. We validate our method by creating three different 3D DGGSs tailored for three specific use cases. These use cases demonstrate our ability to quickly generate 3D global grids while achieving desired properties such as support for large ranges of altitudes, volume preservation between cells, and custom cell aspect ratio. Full article

(This article belongs to the Special Issue Global Grid Systems)

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20 pages, 6493 KiB

Open AccessArticle

Indexing Mixed Aperture Icosahedral Hexagonal Discrete Global Grid Systems

by Rui Wang, Jin Ben, Jianbin Zhou and Mingyang Zheng

ISPRS Int. J. Geo-Inf. 2020, 9(3), 171; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9030171 - 13 Mar 2020

Cited by 11 | Viewed by 3847

Abstract

Discrete global grid systems (DGGSs) are an emerging multiresolution 3D model used to integrate and analyze big earth data. The characteristic of multiresolution is usually realized by hierarchically subdividing cells on the sphere using certain refinement. This paper introduces mixed aperture three- and [...] Read more.

Discrete global grid systems (DGGSs) are an emerging multiresolution 3D model used to integrate and analyze big earth data. The characteristic of multiresolution is usually realized by hierarchically subdividing cells on the sphere using certain refinement. This paper introduces mixed aperture three- and four- icosahedral hexagonal DGGSs using two types of refinement, the various combinations of which can provide more resolutions compared with pure aperture hexagonal DGGSs and can flexibly design the aperture sequence according to the target resolutions. A general hierarchy-based indexing method is first designed, and related indexing arithmetics and algorithm are developed based on the indexing method. Then, the grid structure on the surface of the icosahedron is described and by projection spherical grids are obtained. Experiments show that the proposed scheme is superior to pure aperture schemes in choosing grid resolutions and can reduce the data volume by 38.5% in representing 1-km resolution raster dataset; using the proposed indexing arithmetics to replace spherical geometry operations in generating discrete spherical vector lines based on hexagonal cells can improve the generation efficiency. Full article

(This article belongs to the Special Issue Global Grid Systems)

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16 pages, 7807 KiB

Open AccessArticle

A Topology Preserving Gridding Method for Vector Features in Discrete Global Grid Systems

by Liangchen Zhou, Wenjie Lian, Yudi Zhang and Bingxian Lin

ISPRS Int. J. Geo-Inf. 2020, 9(3), 168; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9030168 - 12 Mar 2020

Cited by 6 | Viewed by 2555

Abstract

Topological distortion seriously affects spatial cognition. To solve this problem caused by the integration of vector features in discrete global grid systems (DGGs), a topology-preserving gridding method for vector features is proposed. The method proposed determines the topological distortion according to the relationship [...] Read more.

Topological distortion seriously affects spatial cognition. To solve this problem caused by the integration of vector features in discrete global grid systems (DGGs), a topology-preserving gridding method for vector features is proposed. The method proposed determines the topological distortion according to the relationship between grid cells and then increases the local resolution of vector features by employing the multi-level resolution characteristic of DGGs, to repair three kinds of topological distortions. Experimental results show that the proposed method can effectively maintain the topological relationship between the original vector features, and the amount of data is stable, thus ensuring the correct integration of vector features in the DGGs. Full article

(This article belongs to the Special Issue Global Grid Systems)

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16 pages, 7032 KiB

Open AccessArticle

Lattice Quad-Tree Indexing Algorithm for a Hexagonal Discrete Global Grid System

by Jianbin Zhou, Jin Ben, Rui Wang, Mingyang Zheng and Lingyu Du

ISPRS Int. J. Geo-Inf. 2020, 9(2), 83; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi9020083 - 31 Jan 2020

Cited by 14 | Viewed by 4309

Abstract

Hexagonal discrete global grid systems are the preferred data models supporting multisource geospatial information fusion. Related research has aroused widespread concern in the academic community, and hierarchical indexing algorithms are one of the main research focuses. In this paper, we propose an algorithm [...] Read more.

Hexagonal discrete global grid systems are the preferred data models supporting multisource geospatial information fusion. Related research has aroused widespread concern in the academic community, and hierarchical indexing algorithms are one of the main research focuses. In this paper, we propose an algorithm for indexing the cell of a ringed spatial area based on a hexagonal lattice quad-tree (HLQT) structure and the indexing characteristics. First, we design a single-resolution indexing algorithm in which indexing starts from the initial quad tree and expands ring by ring using coding operations, and a quad-tree structure is applied to accelerate this process. Second, the hierarchical indexing algorithm is implemented based on single-resolution indexing, and a pyramid hierarchical model is established. Finally, we perform comparison experiments with existing algorithms. The results of the experiments indicate that the single-level indexing efficiency of the proposed algorithm is approximately twice that of the traditional method and that the hierarchical indexing efficiency is approximately 67 times that of the traditional method. These findings verify the feasibility and superiority of the algorithm proposed in this paper. Full article

(This article belongs to the Special Issue Global Grid Systems)

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14 pages, 3748 KiB

Open AccessArticle

Collision Detection for UAVs Based on GeoSOT-3D Grids

by Weixin Zhai, Xiaochong Tong, Shuangxi Miao, Chengqi Cheng and Fuhu Ren

ISPRS Int. J. Geo-Inf. 2019, 8(7), 299; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi8070299 - 15 Jul 2019

Cited by 14 | Viewed by 3913

Abstract

The increasing number of unmanned aerial vehicles (UAVs) has led to challenges related to solving the collision problem to ensure air traffic safety. The traditional approaches employed for collision detection suffer from two main drawbacks: first, the computational burden of a pairwise calculation [...] Read more.

The increasing number of unmanned aerial vehicles (UAVs) has led to challenges related to solving the collision problem to ensure air traffic safety. The traditional approaches employed for collision detection suffer from two main drawbacks: first, the computational burden of a pairwise calculation increases exponentially with an increasing number of spatial entities; second, existing grid-based approaches are unsuitable for complicated scenarios with a large number of objects moving at high speeds. In the proposed model, we first identified UAVs and other spatial objects with GeoSOT-3D grids. Second, the nonrelational spatial database was initialized with a multitable strategy, and spatiotemporal data were inserted with the GeoSOT-3D grid codes as the primary key. Third, the collision detection procedure was transformed from a pairwise calculation to a multilevel query. Four simulation experiments were conducted to verify the feasibility and efficiency of the proposed collision detection model for UAVs in different environments. The results also indicated that 64 m GeoSOT-3D grids are the most suitable basic grid size, and the reduction in the time consumption compared with traditional methods reached approximately 50–80% in different scenarios. Full article

(This article belongs to the Special Issue Global Grid Systems)

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17 pages, 4740 KiB

Open AccessArticle

A Low-Altitude Flight Conflict Detection Algorithm Based on a Multilevel Grid Spatiotemporal Index

by Shuangxi Miao, Chengqi Cheng, Weixin Zhai, Fuhu Ren, Bo Zhang, Shuang Li, Junxiao Zhang and Huangchuang Zhang

ISPRS Int. J. Geo-Inf. 2019, 8(6), 289; https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi8060289 - 21 Jun 2019

Cited by 20 | Viewed by 3979

Abstract

Flight conflict detection is fundamental to flight dispatch, trajectory planning, and flight safety control. An ever-increasing aircraft population and higher speeds, particularly the emergence of hypersonic/supersonic aircrafts, are challenging the timeliness and accuracy of flight conflict detection. Traditional trajectory conflict detection algorithms rely [...] Read more.

Flight conflict detection is fundamental to flight dispatch, trajectory planning, and flight safety control. An ever-increasing aircraft population and higher speeds, particularly the emergence of hypersonic/supersonic aircrafts, are challenging the timeliness and accuracy of flight conflict detection. Traditional trajectory conflict detection algorithms rely on traversing multivariate equations of every two trajectories, in order to yield the conflict result and involve extensive computation and high algorithmic complexity; these algorithms are often unable to provide the flight conflict solutions required quickly enough. In this paper, we present a novel, low-altitude flight conflict detection algorithm, based on the multi-level grid spatiotemporal index, that transforms the traditional trajectory-traversing multivariate conflict computation into a grid conflict state query of distributed grid databases. Essentially, this is a method of exchanging "storage space" for "computational time". First, we build the spatiotemporal subdivision and encoding model based on the airspace. The model describes the geometries of the trajectories, low-altitude obstacles, or dangerous fields and identifies the grid with grid codes. Next, we design a database table structure of the grid and create a grid database. Finally, we establish a multilevel grid spatiotemporal index, design a query optimization scheme, and examine the flight conflict detection results from the grid database. Experimental verification confirms that the computation efficiency of our algorithm is one order of magnitude higher than those of traditional methods. Our algorithm can perform real-time (dynamic/static) conflict detection on both individual aircraft and aircraft flying in formation with more efficient trajectory planning and airspace utilization. Full article

(This article belongs to the Special Issue Global Grid Systems)

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