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1.
ABSTRACT

The aim of site planning based on multiple viewshed analysis is to select the minimum number of viewpoints that maximize visual coverage over a given terrain. However, increasingly high-resolution terrain data means that the number of terrain points will increase rapidly, which will lead to rapid increases in computational requirements for multiple viewshed site planning. In this article, we propose a fast Candidate Viewpoints Filtering (CVF) algorithm for multiple viewshed site planning to lay a foundation for viewpoint optimization selection. Firstly, terrain feature points are selected as candidate viewpoints. Then, these candidate viewpoints are clustered and those belonging to each cluster are sorted according to the index of viewshed contribution (IVC). Finally, the candidate viewpoints with relatively low viewshed contribution rate are removed gradually using the CVF algorithm, through which, the viewpoints with high viewshed contribution are preserved and the number of viewpoints to be preserved can be controlled by the number of clusters. To evaluate the effectiveness of our CVF algorithm, we compare it with the Region Partitioning for Filtering (RPF) and Simulated Annealing (SA) algorithms. Experimental results show that our CVF algorithm is a substantial improvement in both computational efficiency and total viewshed coverage rate.  相似文献   

2.
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3.
Abstract

This paper describes a regional geographical information system (GIS) for some Mediterranean benthic communities. The area covered by the GIS lies between the cities of La Ciotat and Giens in southeast France. The distinctive characteristics of this GIS compared with others usually described in the literature, are that all its layers describe the same theme but as seen at different moments with different scales and techniques used by different oceanographers. A method was devised to synthesize, on a pixel basis, the content of all these layers. Each pixel within each layer is weighted with a function relating to the year of survey, the sampling technique and the scale of the original map corresponding to that layer. The synthesis map is composed of the highest weighted values found in the set of layers. Also at each pixel, conflicts between the contents of layers are quantified and mapped.  相似文献   

4.
As increasingly large‐scale and higher‐resolution terrain data have become available, for example air‐form and space‐borne sensors, the volume of these datasets reveals scalability problems with existing GIS algorithms. To address this problem, a kind of serial algorithm was developed to generate viewshed on large grid‐based digital elevation models (DEMs). We first divided the whole DEM into rectangular blocks in row and column directions (called block partitioning), then processed these blocks with four axes followed by four sectors sequentially. When processing the particular block, we adopted the ‘reference plane’ algorithm to calculate the visibility of the target point on the block, and adjusted the calculation sequence according to the different spatial relationships between the block and the viewpoint since the viewpoint is not always inside the DEM. By adopting the ‘Reference Plane’ algorithm and using a block partitioning method to segment and load the DEM dynamically, it is possible to generate viewshed efficiently in PC‐based environments. Experiments showed that the divided block should be dynamically loaded whole into computer main memory when partitioning, and the suggested approach retains the accuracy of the reference plane algorithm and has near linear compute complexity.  相似文献   

5.
Abstract

This paper presents the development of the first geographical information system (GIS) that may be used to manipulate a single dataset at a very large range of scales (different detail levels). The design of this multi-scale GIS is fully integrated in the open DBMS Postgres and the open GIS GEO + + . Besides the system design, this paper will also give details of the implementation in the Postgres DBMS environment of three generalization tools: 1. the BLG-tree for line and area simplification, 2. the Reactive-tree for selection based on importance and location, and 3. the GAP-tree for solving problems when using the other two structures for an area partitioning. Together with the geographical frontend, the DBMS forms the flexible basis for the realization of powerful GIS applications. The implementation has been successfully benchmarked with two large datasets: World Databank II and DLMS DFAD. The response times improve by one to two orders of magnitude.  相似文献   

6.
Property valuation studies often use classical statistics techniques. Among these techniques, the Artificial Neural Networks are the most applied, overcoming the inflexibility and the linearity of the hedonic models. Other researchers have used Geostatistics techniques, specifically the Kriging Method, for interpreting spatial-temporal variability and to predict housing unit prices. The innovation of this study is to highlight how the Kriging Method can help to better understand the urban environment, improving the results obtained by classical statistics. This study presents two different methods that share the general objective of extracting information regarding a city’s housing from datasets. The procedures applied are Ordinary Kriging (Geostatistics) and Multi-Layer Perceptron algorithm (Artificial Neural Networks). These methods were used to predict housing unit prices in the municipality of Pozuelo de Alarcon (Madrid). The implementation of both methods provides us with the urban characteristics of the study area and the most significant variables related to price. The main conclusion is that the Ordinary Kriging models and the Neural Networks models, applied to predicting housing unit prices are necessary methodologies to improve the information obtained in classical statistical techniques.

Abbreviations: ANN: Artificial Neural Networks; OK: ordinary Kriging; MLP: multi-layer perceptron  相似文献   

7.
Viewshed analysis remains one of the most popular GIS tools for assessing visibility, despite the recognition of several limitations when quantifying visibility from a human perspective. The visual significance of terrain is heavily influenced by the vertical dimension (i.e. slope, aspect and elevation) and distance from the observer, neither of which are adjusted for in standard viewshed analyses. Based on these limitations, this study aimed to develop a methodology which extends the standard viewshed to represent visible landscape as more realistically perceived by a human, called the ‘Vertical Visibility Index’ (VVI). This method was intended to overcome the primary limitations of the standard viewshed by calculating the vertical degrees of visibility between the eye-level of a human and the top and bottom point of each visible cell in a viewshed. Next, the validity of the VVI was assessed using two comparison methods: 1) the known proportion of vegetation visible as assessed through imagery for 10 locations; and 2) standard viewshed analysis for 50 viewpoints in an urban setting. While positive, significant correlations were observed between the VVI values and both comparators, the correlation was strongest between the VVI values and the image verified, known values (r = 0.863, p = 0.001). The validation results indicate that the VVI is a valid method which can be used as an improvement on standard viewshed analyses for the accurate representation of landscape visibility from a human perspective.  相似文献   

8.
Abstract

Geographical Information Systems can be used for processing spatial data to assess the risks of environmental contamination. Their use depends upon the amount and quality of available data, the models for interpolation and calculation of health risk, data processing procedures and interactivity. In this study, it is shown that interactive use of GIS is important for obtaining physically relevant results. Three forms of interactivity are distinguished: interactivity by means of user interfacing, interactivity requiring additional information outside GIS and interactivity when changing the use of GIS. Three stages in which interaction with GIS are crucial can be distinguished: application of geostatistics, choice of appropriate models, and decision making. This study focuses on three cases in The Netherlands dealing with soil contamination and soil stress analysis and with implications for risk assessment in which interactivity within GIS is analysed. Emphasis is given to contour volumes of polluted soil, to combine GIS with deterministic models and to apply land use scenarios. Finally, there is a discussion of how some forms of interactivity could be replaced by expert systems.  相似文献   

9.
《The Journal of geography》2012,111(5):258-263
Abstract

Many universities are introducing courses to teach students the principles of geographic information systems (GIS). In addition to lectures, exercises with commercial GIS software are offered to show basic operations. Although students learn to execute such operations, the software may hide their internal structure and logic. We propose using a spreadsheet program as a teaching tool for raster operations such as filter and overlay. Spreadsheets offer a practical way to demonstrate and experiment with raster operations, because the raster structure is captured in the form of rows and columns. With this tool, students are able to perform and visualize operations as well as to see how the data are processed by the algorithms. Our approach is new in that we concentrate on the algorithms of operations. We make explicit which raster functions are actually evaluated when performing a particular operation. We conclude that there are good reasons for using spreadsheets in comparison to traditional GIS software when teaching raster operations. These are demonstration in class, simple user interface, familiarity to students, low cost, flexibility of changing cell values, ease of changing parameters, easy programming environment, and the possibility to look behind the scenes of operations by viewing the code.  相似文献   

10.
Selecting the set of candidate viewpoints (CVs) is one of the most important procedures in multiple viewshed analysis. However, the quantity of CVs remains excessive even when only terrain feature points are selected. Here we propose the Region Partitioning for Filtering (RPF) algorithm, which uses a region partitioning method to filter CVs of a multiple viewshed. The region partitioning method is used to decompose an entire area into several regions. The quality of CVs can be evaluated by summarizing the viewshed area of each CV in each region. First, the RPF algorithm apportions each CV to a region wherein the CV has a larger viewshed than that in other regions. Then, CVs with relatively small viewshed areas are removed from their original regions or reassigned to another region in each iterative step. In this way, a set of high-quality CVs can be preserved, and the size of the preserved CVs can be controlled by the RPF algorithm. To evaluate the computational efficiency of the RPF algorithm, its performance was compared with simple random (SR), simulated annealing (SA), and ant colony optimization (ACO) algorithms. Experimental results indicate that the RPF algorithm provides more than a 20% improvement over the SR algorithm, and that, on average, the computation time of the RPF algorithm is 63% that of the ACO algorithm.  相似文献   

11.
ABSTRACT

The purpose of this study is to examine local level spatiotemporal rainfall and temperature variability in drought-prone districts of rural Sidama, Central Rift Valley region of Ethiopia. The study used 129 gridded monthly rainfall and temperature data of 32 years (1983–2014). The gridded rainfall and temperature records were encoded into GIS software and evaluated through different statistical and geospatial techniques. Mann-Kendal rank test and F distribution tests were used to test temporal and spatial statistical significance, respectively, of the data. The analysis revealed that Belg and Kiremt are the main rainfall seasons, constituting 81% of the annual rainfall. Although annual, Kiremt, and Belg rainfall amounts appear to have decreased over time, the decreasing trend is statistically significant only for Belg rainfall records. On the other hand, rainfall standard anomaly results indicated seven droughts of different magnitudes: one extreme, two severe, and four moderate. The study also revealed increasing temperature trends over the years under consideration that are statistically significant. The findings of this study on rainfall contradict other findings obtained around the study area. Thus, climate change adaptations need to focus on location-specific climate data analysis so that the intended adaptive interventions can be successful.  相似文献   

12.
ABSTRACT

Six routing algorithms, describing how flow (and water borne material) will be routed over Digital Elevation Models, are described and compared. The performance of these algorithms is determined based on both the calculation of the contributing area and the prediction of ephemeral gullies. Three groups of routing algorithms could be identified. Both from a statistical and a spatial viewpoint these groups produce significantly different results, with a major distinction between single flow and multiple flow algorithms. Single flow algorithms cannot accommodate divergent flow and are very sensitive to small errors. Therefore, they are not acceptable for hillslopes. The flux decomposition algorithm, proposed here, seems to be preferable to other multiple flow algorithms as it is mathematically straightforward, needs only up to two neighbours and yields more realistic results for drainage lines. The implications of the routing algorithms on the prediction of ephemeral gullies seem to be somewhat counterintuitive: the single flow algorithms that, at first sight, seem to mimic the process of overland flow, do not yield optimal prediction results.  相似文献   

13.
Abstract

Representations historically used within GIS assume a world that exists only in the present. Information contained within a spatial database may be added-to or modified over time, but a sense of change or dynamics through time is not maintained. This limitation of current GIS capabilities has recently received substantial attention, given the increasingly urgent need to better understand geographical processes and the cause-and-effect interrelationships between human activities and the environment. Models proposed so-far for the representation of spatiotemporal data are extensions of traditional raster and vector representations that can be seen as location- or feature-based, respectively, and are therefore best organized for performing either location-based or feature-based queries. Neither form is as well-suited for analysing overall temporal relationships of events and patterns of events throughout a geographical area as a temporally-based representation.

In the current paper, a new spatio-temporal data model is proposed that is based on time as its organizational basis, and is thereby intended to facilitate analysis of temporal relationships and patterns of change through time. This model is named the Event-based Spatio Temporal Data Model (ESTDM). It is shown that temporally-based queries relating to locations can be implemented in an efficient and conceptually straightforward manner using ESTDM by describing algorithms for three fundamental temporally-based retrieval tasks based on this model: (1) retrieving location(s) that changed to a given value at a given time, (2) retrieving location(s) that changed to a given value over a given temporal interval, and (3) calculation of the total area that has changed to a given value over a given temporal interval. An empirical comparison of the space efficiency of ESTDM and compressed and uncompressed forms of the ‘snapshot’ model is also given, showing that ESTDM is also a compact representation of spatio-temporal information.  相似文献   

14.
A Pedagogic Framework to Link GIS to the Intellectual Core of Geography   总被引：4，自引：3，他引：1  
《The Journal of geography》2012,111(6):578-591
Abstract

This paper aims to develop a new pedagogic framework for teaching GIS at the college and university level using Berry's geographic matrix. By synthesizing different schools of thought, this paper argues that GIS education essentially involves two aspects—how to teach about GIS and how to teach with GIS. Berry's geographic matrix can be used to tie these dual aspects of GIS education together neatly. As an abstract representation of geographical phenomena, the geographic matrix embeds all three entities of GIS—location, attribute, time—and thus can help GIS instructors teach about GIS. As a synthesis of geographical approaches, the geographic matrix can assist GIS instructors teach with GIS. This paper demonstrates that GIS is actually an implementation of Berry's geographic matrix. Furthermore, the 10 approaches to geographical analysis, originally proposed by Berry for the geographic matrix, can be executed routinely in a GIS environment. By incorporating Berry's geographic matrix into GIS education, teachers can enable students to surpass technical issues and to appreciate the conceptual and functional linkages between GIS and geography's intellectual core.  相似文献   

15.

Cartographic visualisation tools aid exploration, but they are designed for, and used exclusively by, experts. A democratised visualisation tool will include second-generation users, and these non-specialists might also want to use the available computer technology to visualise their geographical data. In this paper, we argue that democratised GIS should have a functionality similar to visualisation tools and we forward our opinion on how these can be developed in order to do so. Our emphasis is on interactivity regarding representation methods and on elaborating principles for implementing map type selection in interfaces for democratised GISs.  相似文献   

16.
基于GIS的山洪灾害风险区划   总被引：1，自引：0，他引：1  
1 Introduction Torrent is sudden surface runoff with sharp rises or falls (Tang, 1994; Zhao, 1996), resulting from rainfall in small basins of mountainous areas. It has features of violent coming force, rapid formation and strong destructivity which rende…  相似文献   

17.
Abstract

Application of Geographical Information Systems (GIS) to environmental problems requires a spatial delineation of soil properties and some a priori knowledge of their variability. In the U.S.A. estimated soil properties are available from soil surveys published by the National Cooperative Soil Survey. However, information on the extent and nature of their variability is generally lacking. To remedy the situation, variability of selected soil properties measured at farm and watershed scales was compared with published values using geostatistical methods. Results showed that the variability of bulk density and hydraulic conductivity can be estimated by comparing regularized variograms of measured and published values. An overlay method was proposed that combines measured and published delineations of soil properties into an overlay with the properties of both. The technique makes it possible to incorporate variability into a GIS analysis using data available from published soil surveys.  相似文献   

18.
Abstract

A neglected aspect of facility location problems is the geometric representation of the facilities sited and clients served. Point objects represent these entities in most facility location problems. This can cause solution error and limit the range of potential solutions. The increasing capabilities of geographical information systems (GIS) to represent, store and manipulate spatial entities provides a substantial but unrealized potential for more sophisticated geometric representation in facility location problems. This paper provides a framework for realizing this potential. Specifically, this paper: (i) synthesizes existing formulations; (ii) develops a unified mathematical framework; (iii) identifies feasible computational strategies that can be implemented within a GIS framework, and; (iv) discusses potential GIS-based solution algorithms.  相似文献   

19.
ABSTRACT

Road intersection data have been used across a range of geospatial analyses. However, many datasets dating from before the advent of GIS are only available as historical printed maps. To be analyzed by GIS software, they need to be scanned and transformed into a usable (vector-based) format. Because the number of scanned historical maps is voluminous, automated methods of digitization and transformation are needed. Frequently, these processes are based on computer vision algorithms. However, the key challenges to this are (1) the low conversion accuracy for low quality and visually complex maps, and (2) the selection of optimal parameters. In this paper, we used a region-based deep convolutional neural network-based framework (RCNN) for object detection, in order to automatically identify road intersections in historical maps of several cities in the United States of America. We found that the RCNN approach is more accurate than traditional computer vision algorithms for double-line cartographic representation of the roads, though its accuracy does not surpass all traditional methods used for single-line symbols. The results suggest that the number of errors in the outputs is sensitive to complexity and blurriness of the maps, and to the number of distinct red-green-blue (RGB) combinations within them.  相似文献   

20.
Abstract

A geographical information system (GIS) based study was carried out in a densely-populated watershed in Nepal. An evaluation of land use change between 1972 and 1990 indicated that there has been an increase in forest and agricultural land area and a decrease in shrubland and grassland area. GIS techniques were used to produce single and composite fertility index maps, which can be used for problem identification and planning. These maps indicate that forest soil fertility is generally poor in the watershed. GIS was found to be very beneficial in addressing critical resource issues in small watersheds in developing countries.  相似文献   

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