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1.
GPU加速的多边形叠加分析   总被引：2，自引：0，他引：2  
叠加分析是地理信息系统最重要的分析功能之一,对多边形图层进行叠加分析要花费大量时间。为此,将GPU用于多边形叠加分析过程中的MBR过滤及多边形剪裁两个阶段。对MBR过滤阶段,提出了基于GPU的通过直方图及并行前置和实现的MBR过滤算法。对多边形剪裁阶段,通过改进Weiler-Atherton算法,使用新的焦点插入方法和简化的出入点标记算法,并结合并行前置和算法,提出了基于GPU的多边形剪裁算法。对实现过程中可能出现的负载不均衡情况,给出了基于动态规划的负载均衡方法。通过对这些算法的应用,实现对过滤阶段及精炼阶段的加速。实验结果表明,基于GPU的MBR过滤方法相对CPU实现的加速比为3.8,而基于GPU的多边形剪裁的速度比CPU实现快3.4倍。整体上,与CPU实现相比,GPU加速的多边形叠加提供了3倍以上的加速比。  相似文献   

2.
Qualitative knowledge representation of spatial locations and relations is popular in many text-based media, for example, postings on social networks, news reports, and encyclopedia, as representing qualitative spatial locations is indispensable to infer spatial knowledge from them. However, an integrative model capable of handling direction-based locations of various spatial objects is missing. This study presents an integrative representation and inference framework about direction-based qualitative locations for points, lines, and polygons. In the framework, direction partitions of different types of reference objects are first unified to create a partition consisting of cells, segments, and corners. They serve as a frame of reference to locate spatial objects (e.g., points, lines, and polygons). Qualitative relations are then defined to relate spatial objects to the elements in a cell partition, and to form the model of qualitative locations. Last, based on the integrative representation, location-based reasoning mechanism is presented to derive topological relations between objects from their locations, such as point–point, line–line, point–line, point–polygon, line–polygon, and polygon–polygon relations. The presented model can locate any type of spatial objects in a frame of reference composed of points, lines, and polygons, and derive topological relations between any pairs of objects from the locations in a unified method.  相似文献   

3.
Facility placement and associated service coverage are major concerns in urban and regional planning. In this paper an approach is detailed for the problem of covering spatial demand for service, where potential facilities are located in the continuous plane. It is shown that weighted demand, represented as points, lines or polygons, can be optimally served by a finite number of potential facility locations, called the polygon intersection point set (PIPS). The developed approach is an extension of a point‐based abstraction of demand to more general representations (e.g. points, lines or polygons). An empirical analysis of warning siren siting in Ohio is carried out, highlighting the applicability of this approach.  相似文献   

4.
Polygonal vector data are important for representing countries, lakes, residential settlements, and other polygonal features. The proper representation of polygonal vector data is the basis of efficient rendering and picking and quick access and display of the analysis results based on polygons (e.g., 3D overlaying and surface area measurement in mountainous areas) in a virtual globe. However, polygonal vector data are displayed using texture-based or boundary-based approaches in most existing virtual globes. The texture-based approach cannot easily support interactive operations (e.g., picking) and spatial analysis (e.g., adjacency analysis and spatial measurement). The boundary-based approach treats the holes as independent features; however, it is difficult to recognize which boundaries constitute a polygon. Further research is needed on how to better organize the polygons to support efficient rendering, picking, and analysis in a virtual globe. In this article, we propose two methods to drape interior filled 2D polygons onto a multi-resolution 3D terrain. Both proposed methods combine polygon clipping and polygon triangulation. The difference between the two methods is in the way holes are eliminated. Method 1 recursively subdivides a terrain triangle until the child-triangles contain no holes; every resulting clipped polygon, which is then triangulated, contains no holes. Method 2 directly clips a polygon against a terrain triangle and creates bridge edges to transform the resulting polygons with holes to degenerate polygons that are further triangulated. The experimental results demonstrate that both proposed methods can efficiently process polygons with holes resulting in appropriate numbers of triangles. The processed interior-filled polygons remain close to the terrain surface in a virtual globe. Both proposed methods support real-time rendering of polygonal vector data in a virtual globe.  相似文献   

5.
简单要素模型下多边形叠置分析算法   总被引：1，自引：0，他引：1  
现有的矢量空间叠置分析多采用拓扑模型,要求建立完整的数据拓扑关系。该文采用简单要素模型,以多边形叠置交运算为例,介绍简单要素模型下空间叠置分析的具体实现,着重讨论多边形交运算的交替搜索算法,在线段求交中对连续出入点、重交点等特殊数据进行处理。在实际应用中,该算法可较好解决大规模复杂数据层的叠置交运算,比同规模的拓扑叠置运算效率高。  相似文献   

6.
Intersection relations are important topological considerations in database update processes. The differentiation and identification of non-empty intersection relations between new updates and existing objects is one of the first steps in the automatic incremental update process for a land parcel database. The basic non-empty intersection relations are meet, overlap, cover, equal and inside, but these basic relationships cannot reflect the complex and detailed non-empty relations between a new update and the existing objects. It is therefore necessary to refine the basic non-empty topological relations to support and trigger the relevant update operations. Such relations have been refined by several researchers using topological invariants (e.g., dimension, type and sequence) to represent the intersection components. However, the intersection components often include only points and lines, and the refined types of 2-dimensional intersection components that occur between land parcels have not been defined. This study examines the refinement of non-empty relations among 2-dimensional land parcels and proposes a computation model. In this model, an entire spatial object is directly used as the operand, and two set operations (i.e., intersection (∩) and difference (\)) are applied to form the basic topological computation model. The Euler number is introduced to refine the relations with a single 2-dimensional intersection (i.e., cover, inside and overlap) and to distinguish the refined types of 2-dimensional intersection components for the relations with multiple intersections. In this study, the cover and overlap relations with single intersections between regions are refined into seven cases, and nine basic types of 2-dimensional intersection components are distinguished. A composite computation model is formed with both Euler number values and dimensional differences. In this model, the topological relations with single intersections are differentiated by the value of the dimension and the Euler number of the resulting set of the whole-object intersection and differences, whereas the relations with multiple intersections are discriminated by the value of the resulting set at a coarse level and are further differentiated by the type and sequence of the whole-object intersection component in a hierarchical manner. Based on the refined topological relations, an improved method for automatic and incremental updating of the land parcel database is presented. The effectiveness of the models and algorithms was verified by the incremental update of a land cover database. The results of this study represent a new avenue for automatic spatial data handling in incremental update processes.  相似文献   

7.
多边形是GIS研究和应用中使用最频繁的几何对象,该文描述了基于简单要素模型的任意多边形分割算法。从计算几何出发,结合GIS空间数据的特点,将基于简单要素模型的多边形分割算法设计为:1)对多边形及分割线的边界排序,基于扫描线及外包矩形检测查找可能相交的线段,提高相交线段的搜索效率;2)计算交点生成结点信息(包括交点坐标、线号及交点的出入),并存储在独立的单向链表中;3)根据结点链表和原多边形坐标搜索结果多边形。该算法能够分割任意简单多边形(凹凸、曲线边界和带洞的多边形)以及有共享边的多边形。最后在MapGIS7.0平台上,实现了基于简单要素类的多边形分割功能。  相似文献   

8.
The availability of continental and global-scale spatio-temporal geographical data sets and the requirement to efficiently process, analyse and manage them led to the development of the temporally enabled Geographic Resources Analysis Support System (GRASS GIS). We present the temporal framework that extends GRASS GIS with spatio-temporal capabilities. The framework provides comprehensive functionality to implement a full-featured temporal geographic information system (GIS) based on a combined field and object-based approach. A significantly improved snapshot approach is used to manage spatial fields of raster, three-dimensional raster and vector type in time. The resulting timestamped spatial fields are organised in spatio-temporal fields referred to as space-time data sets. Both types of fields are handled as objects in our framework. The spatio-temporal extent of the objects and related metadata is stored in relational databases, thus providing additional functionalities to perform SQL-based analysis. We present our combined field and object-based approach in detail and show the management, analysis and processing of spatio-temporal data sets with complex spatio-temporal topologies. A key feature is the hierarchical processing of spatio-temporal data ranging from topological analysis of spatio-temporal fields over boolean operations on spatio-temporal extents, to single pixel, voxel and vector feature access. The linear scalability of our approach is demonstrated by handling up to 1,000,000 raster layers in a single space-time data set. We provide several code examples to show the capabilities of the GRASS GIS Temporal Framework and present the spatio-temporal intersection of trajectory data which demonstrates the object-based ability of our framework.  相似文献   

9.
基于DEM的复杂地形流域特征提取   总被引：19，自引：2，他引：19  
利用流域数字高程模型(DEM)构建数字水系模型并提取流域水系特征是分布式水文过程模拟的重要前提。提出了面向分布式水文过程模拟和流域特征提取的数字水系模型,并针对现有方法对复杂地形DEM中含有的平地、洼地及其嵌套情形的处理不足,提出了栅格水流分类、填洼分类与归并及有效填平处理、河谷平地的出流代价法构建栅格流向和流序等新的处理方法,并在开发的软件系统得到实现。使用该方法创建的黄土岭流域数字水系模型和提取的水系等流域特征结果表明:本文方法可有效应对复杂地形流域的处理,提取的流域水系特征与实际自然水系比较吻合,能够有效地消除现有方法在地形平坦区域容易产生的平行河道、奇异河道、河道变形等不足。  相似文献   

10.
With the wide adoption of big spatial data and the emergence of CyberGIS, the nontrivial computational intensity introduced by massive amount of data poses great challenges to the performance of vector map visualization. The parallel computing technologies provide promising solutions to such problems. Evenly decomposing the visualization task into multiple subtasks is one of the key issues in parallel visualization of vector data. This study focuses on the decomposition of polyline and polygon data for parallel visualization. Two key factors impacting the computational intensity were identified: the number of features and the number of vertices of each feature. The computational intensity transform functions (CITFs) were constructed based on the linear relationships between the factors and the computing time. The computational intensity grid (CIG) can then be constructed using the CITFs to represent the spatial distribution of computational intensity. A noninterlaced continuous space-filling curve is used to group the lattices of CIG into multiple sub-domains such that each sub-domain entails the same amount of computational intensity as others. The experiments demonstrated that the approach proposed in this paper was able to effectively estimate and spatially represent the computational intensity of visualizing polylines and polygons. Compared with the regular domain decomposition methods, the new approach generated much more balanced decomposition of computational intensity for parallel visualization and achieved near-linear speedups, especially when the data is greatly heterogeneously distributed in space.  相似文献   

11.
In the map of geo-referenced population and cases, the detection of the most likely cluster (MLC), which is made up of many connected polygons (e.g., the boundaries of census tracts), may face two difficulties. One is the irregularity of the shape of the cluster and the other is the heterogeneity of the cluster. A heterogeneous cluster is referred to as the cluster containing depression links (a polygon is a depression link if it satisfies two conditions: (1) the ratio between the case number and the population in the polygon is below the average ratio of the whole map; (2) the removal of the polygon will disconnect the cluster). Previous studies have successfully solved the problem of detecting arbitrarily shaped clusters not containing depression links. However, for a heterogeneous cluster, existing methods may generate mistakes, for example, missing some parts of the cluster. In this article, a spatial scanning method based on the ant colony optimization (AntScan) is proposed to improve the detection power. If a polygon can be simplified as a node, the research area consisting of many polygons then can be seen as a graph. So the detection of the MLC can be seen as the search of the best subgraph (with the largest likelihood value) in the graph. The comparison between AntScan, GAScan (the spatial scan method based on the genetic optimization), and SAScan (the spatial scan method based on the simulated annealing optimization) indicates that (1) the performance of GAScan and SAScan is significantly influenced by the parameter of the fraction value (the maximum allowed size of the detected cluster), which can only be estimated by multiple trials, while no such parameter is needed in AntScan; (2) AntScan shows superior power over GAScan and SAScan in detecting heterogeneous clusters. The case study on esophageal cancer in North China demonstrates that the cluster identified by AntScan has the larger likelihood value than that detected by SAScan and covers all high-risk regions of esophageal cancer whereas SAScan misses some high-risk regions (the region in the southwest of Shandong province, eastern China) due to the existence of a depression link.  相似文献   

12.
This paper discusses the issues of positional accuracy and measurement error in the context of a large empirical study of landscape change in England and Wales. The epsilon band model of digitizing accuracy is used to make estimates of the levels of positional uncertainty and measurement error that is due to digitizing polygon outlines. The degree of error expected had the same polygons been captured in raster format is then determined. These results prompt a general discussion of the nature of error in spatial databases.  相似文献   

13.
A new method is illustrated for describing the characteristics of urban pattern changes over different time periods. This method employs vector geometry, paired centroids, shared boundary lines, and overlain polygons. Three new statistics are proposed for characterizing local polygon feature changes in quantity, shape, and size. These statistics are standardized, based on conventional theories from urban geography such as directional concentric zones and user‐designated corridors to document both regional and global patterns of land‐use change. This method is used to analyse land‐use changes in metropolitan Detroit between 1990 and 2000. The Detroit case study indicates that the CTSPA statistics are effective in describing urban spatial pattern changes and in characterizing the evolution of discrete urban landscapes over selected periods.  相似文献   

14.
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15.
提出GIS多边形倒金字塔模型,拓展了模型能够支持的数据结构与适用范围,使其可以应用于普通GIS电子地图中,为采用预生成不同比例尺图面多分辨率表达无极比例尺图形显示技术提供了模型支持,并给出了建模方法,使普通GIS多边形的无极比例尺显示可以依据精度标准进行局部更新和无冗余存储。  相似文献   

16.
中国省级人口增长率及其空间关联分析   总被引：38，自引：0，他引：38  
分析了1982－1990年和1990－1998年2个时期的人口增长率，并用空间统计分析方法研究了2个时期人口增长率的空间关联关系。1982－1990年中国可分为北部人口低增长、中西部高人口增长率、中东部低人口增长率和南部高人口增长率等4个区域，1990－1998年中国可分为北部低人口增长率和南部高人口增长率2个区域，2个时期的空间聚类虽然不完全相同，但它们有共同的特点，南部和西部的人口增长率都比较高，北部地区的人口增长率都比较低，但它们有共同的特点，南部和西部的人口增长率都比较高，北部地区的人口增长率都比较低。最后对实证研究的结果进行了分析。  相似文献   

17.
分布式水文模型的并行计算研究进展   总被引：3，自引：1，他引：2  
大流域、高分辨率、多过程耦合的分布式水文模拟计算量巨大,传统串行计算技术不能满足其对计算能力的需求,因此需要借助于并行计算的支持。本文首先从空间、时间和子过程三个角度对分布式水文模型的可并行性进行了分析,指出空间分解的方式是分布式水文模型并行计算的首选方式,并从空间分解的角度对水文子过程计算方法和分布式水文模型进行了分类。然后对分布式水文模型的并行计算研究现状进行了总结。其中,在空间分解方式的并行计算方面,现有研究大多以子流域作为并行计算的基本调度单元;在时间角度的并行计算方面,有学者对时空域双重离散的并行计算方法进行了初步研究。最后,从并行算法设计、流域系统综合模拟的并行计算框架和支持并行计算的高性能数据读写方法3个方面讨论了当前存在的关键问题和未来的发展方向。  相似文献   

18.
Cartographic modelling operations provide powerful tools for analysing and manipulating geographic data in the raster data model. This research extends these operations to the vector data model. It first discusses how the spatial scopes of analysis can be defined for point, line, and polygon features analogous to the raster cell. Then it introduces the local, focal, and zonal operations available for vector features, followed by providing a prototype syntax that might guide the implementation of these operations. Through example applications, this research also demonstrates the usefulness of these operations by comparing them with traditional vector spatial analysis.  相似文献   

19.
土地利用数据尺度转换的精度损失分析   总被引：10，自引：0，他引：10  
由于栅格数据便于空间分析,因而通常将矢量数据转化成栅格数据来进行空间分析.在转化过程中,选用不同的栅格大小,其面积和精度损失是不同的.针对这个问题,以重庆市110万的土地利用矢量数据为例,探讨了不同栅格大小下,各种土地利用类型在转化过程的面积和精度损失.研究表明(1)栅格大小＜100m时,其精度损失均＜3.3%.(2)在1000m时,其精度损失达到50%以上的地类有湖泊、水库坑塘、滩地、农村居民点用地、工交建设用地、戈壁、裸岩石地、平原区旱地和坡度＞25°的旱地,这些地类的平均图斑大小均在＜51hm2.(3)在30m～1000m间,平均图斑大小＜82hm2的地类随着栅格的由小变大,其面积变得比实际面积小;平均图斑大小＞101hm2的地类中除高盖度的草地和河渠之外,却与此相反.  相似文献   

20.
Land-use/cover change (LUCC) projections can be generated by a variety of land-cover change models (LCMs) and applied to a range of ecological and environmental studies. Most existing spatially explicit LCMs represent land use or cover using either pixel or polygon/patch spatial units. However, the effects of the choice to use pixel versus polygonal land units on the outputs from any given model have not yet been systematically assessed. We evaluated the impacts of alternative land units on the performance of a LCM. A stochastic LCM based on a geostatistical algorithm was developed and applied using both pixel and polygons, which were derived from parcel maps. Nine possible parcel-change scenarios were generated to evaluate the effects of geometric change in management boundaries. The approach was tested through the simulation of multiple land-cover transitions in Medina County, Ohio, between 1992 and 2011. Performance of the simulations was assessed using a metric for the accuracy of spatial allocations (figure of merit (FoM)) and several landscape pattern metrics describing the shapes and sizes of resulting land-cover patches. Results support the notion that there is a clear trade-off between pixel and polygon land units: using polygon boundaries is helpful in obtaining more realistic spatial patterns, but at the cost of location accuracy. Significant differences were found among different parcel-change scenarios on both location accuracy and spatial patterns, with the primary effects being dependent on the type of land-cover transition and the resolution at which validation was assessed.  相似文献   

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