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1.
基于GIS的任意发生元Voronoi图逼近方法   总被引：7，自引：1，他引：6  
许多地理问题的空间分析中需要采用Voronoi图,但是目前我们尚缺乏一些简单的易于实现的构建任意发生元Voronoi图的方法,也缺乏一个能直接生成任意发生元Voronoi图的软件,为此我们提出了一种基于GIS的构建任意发生元的未加权Voronoi图的逼近方法。首先用有限点来逼近原始发生元,然后构建这些点发生元Voronoi图,最后消除那些属于同一发生元的顶点和边,即得到原始发生元的逼近的Voronoi图。在该算法的具体实现过程中,充分利用了现有GIS软件可以生成点发生元Voronoi图的特性和处理空间数据的能力。试验结果表明,这种方法可以生成未加权的任意形状发生元的逼近Voronoi图,能满足地理问题空间分析的需要。如地理客体可以是点状地理客体(城市、县城、交通枢纽、商业中心和金融中心等)、线状地理客体(交通运输线、经济地带和河系等)、面状地理客体(经济区、公园和绿地等)或者它们的组合,它们的空间影响范围或空间服务范围都可以采用Voronoi图来界定。  相似文献   

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4.
As a basic and significant operator in map generalization, polyline simplification needs to work across scales. Perkal’s ε-circle rolling approach, in which a circle with diameter ε is rolled on both sides of the polyline so that the small bend features can be detected and removed, is considered as one of the few scale-driven solutions. However, the envelope computation, which is a key part of this method, has been difficult to implement. Here, we present a computational method that implements Perkal’s proposal. To simulate the effects of a rolling circle, Delaunay triangulation is used to detect bend features and further to construct the envelope structure around a polyline. Then, different connection methods within the enveloping area are provided to output the abstracted result, and a strategy to determine the best connection method is explored. Experiments with real land-use polygon data are implemented, and comparison with other algorithms is discussed. In addition to the scale-specificity inherited from Perkal’s proposal, the results show that the proposed algorithm can preserve the main shape of the polyline and meet the area-maintaining constraint during large-scale change. This algorithm is also free from self-intersection.  相似文献   

5.
基于道路网络的商业网点市场域分析   总被引：6，自引：0，他引：6  
社会经济活动中人们的空间行为往往是基于道路网络来实现的。但是,目前多数研究都假设地理空间是一个均质空间,采用基于平面欧氏距离的空间分析方法,这是有局限的。本文阐述了基于网络距离的网络Voronoi图基本概念和实现方法,以武汉市商业零售连锁企业为例,分别采用基于欧氏距离的普通Voronoi图方法和基于网络距离的网络Voronoi图方法来确定商业零售网点的市场域,结果表明武汉市主城区商业网点市场域较小、主城区外围市场域较大。市场域大小与城市路网密度呈现一定相关关系,路网密度高、市场域小,路网密度低、市场域大。两种方法的计算结果存在一定差异,差异大小与路网密度有关,路网密度大、差异小,路网密度小、差异大。这表明在路网密度大的情况下,可以采用普通Voronoi图粗略地模拟商业网点的市场域。  相似文献   

6.
CityGML (City Geography Markup Language), the OGC (Open Open Geospatial Consortium) standard on three-dimensional (3D) city modeling, is widely used in an increasing number of applications, because it models a city with rich geometrical and semantic information. The underlying building model differentiates four consecutive levels of detail (LoDs). Nowadays, most city buildings are reconstructed in LoD3, while few landmarks in LoD4. For visualization or other purposes, buildings in LoD2 or LoD1 need to be derived from LoD3 models. But CityGML does not indicate methods for the automatic derivation of the different LoDs. This article presents an approach for deriving LoD2 buildings from LoD3 models which are essentially the exterior shells of buildings without opening objects. This approach treats different semantic components of a building separately with the aim to preserve the characteristics of ground plan, roof, and wall structures as far as possible. The process is composed of three steps: simplifying wall elements, generalizing roof structures, and then reconstructing the 3D building by intersecting the wall and roof polygons. The first step simplifies ground plan with wall elements projected onto the ground. A new algorithm is developed to handle not only simple structures like parallel and rectangle shapes but also complicated structures such as non-parallel, non-rectangular shapes and long narrow angles. The algorithm for generalizing roof structure is based on the same principles; however, the calculation has to be conducted in 3D space. Moreover, the simplified polygons of roof structure are further merged and typified depending on the spatial relations between two neighboring polygons. In the third step, generalized 3D buildings are reconstructed by increasing walls in height and intersecting with roof structures. The approach has been implemented and tested on a number of 3D buildings. The experiments have verified that the 3D building can be efficiently generalized, while the characteristics of wall and roof structure can be well preserved after the simplification.  相似文献   

7.
Several algorithms have been proposed to generate a polygonal ‘footprint’ to characterize the shape of a set of points in the plane. One widely used type of footprint is the χ-shape. Based on the Delaunay triangulation (DT), χ-shapes guaranteed to be simple (Jordan) polygons. This paper presents for the first time an incremental χ-shape algorithm, capable of processing point data streams. Our incremental χ-shape algorithm allows both insertion and deletion operations, and can handle streaming individual points and multiple point sets. The experimental results demonstrated that the incremental algorithm is significantly more efficient than the existing, batch χ-shape algorithm for processing a wide variety of point data streams.  相似文献   

8.
This paper reviews the utility of polygon centroid algorithms for natural resource management applications. Following a review of ‘standard’ centroid derivation algorithms, and their limitations, alternative approaches are proposed. Building upon current polygon-reduction algorithms an iterative edge-erosion model is presented. Resilient centroids derived via this model are shown to: (1) maximise the distance to all internal and external edges; (2) be located within the polygon boundary; and (3) be insensitive to patch vertex outliers.

The resilient centroid is demonstrated to have utility in a range of natural resource management applications including the matching of disparate data sources. Exemplar studies conclude that resilient centroids support an appropriate allocation of vegetation condition point samples both within and between native vegetation patches. Further, the utilisation of resilient centroids enables the (1) sub-division of vegetation patches into homogenous regions (core areas) and (2) interrogation of the relationship between vegetation condition and core area proximity.  相似文献   

9.
In this article we show that the Voronoi-based nine-intersection (V9I) model proposed by Chen et al. (2001, A Voronoi-based 9-intersection model for spatial relations. International Journal of Geographical Information Science, 15 (3), 201–220) is more expressive than what has been believed before. Given any two spatial entities A and B, the V9I relation between A and B is represented as a 3 × 3 Boolean matrix. For each pair of types of spatial entities that is, points, lines, and regions, we first show that most Boolean matrices do not represent a V9I relation by using topological constraints and the definition of Voronoi regions. Then, we provide illustrations for all the remaining matrices. This guarantees that our method is sound and complete. In particular, we show that there are 18 V9I relations between two areas with connected interior, while there are only nine four-intersection relations. Our investigations also show that, unlike many other spatial relation models, V9I relations are context or shape sensitive. That is, the existence of other entities or the shape of the entities may affect the validity of certain relations.  相似文献   

10.
This article presents a geometric algebra-based model for topological relation computation. This computational model is composed of three major components: the Grassmann structure preserving hierarchical multivector-tree representation (MVTree), multidimensional unified operators for intersection relation computation, and the judgement rules for assembling the intersections into topological relations. With this model, the intersection relations between the different dimensional objects (nodes at different levels) are computed using the Tree Meet operator. The meet operation between two arbitrary objects is accomplished by transforming the computation into the meet product between each pair of MVTree nodes, which produces a series of intersection relations in the form of MVTree. This intersection tree is then processed through a set of judgement rules to determine the topological relations between two objects in the hierarchy. Case studies of topological relations between two triangles in 3D space are employed to illustrate the model. The results show that with the new model, the topological relations can be computed in a simple way without referring to dimension. This dimensionless way of computing topological relations from geographic data is significant given the increased dimensionality of geographic information in the digital era.  相似文献   

11.
Territory or zone design processes entail partitioning a geographic space, organized as a set of areal units, into different regions or zones according to a specific set of criteria that are dependent on the application context. In most cases, the aim is to create zones of approximately equal sizes (zones with equal numbers of inhabitants, same average sales, etc.). However, some of the new applications that have emerged, particularly in the context of sustainable development policies, are aimed at defining zones of a predetermined, though not necessarily similar, size. In addition, the zones should be built around a given set of seeds. This type of partitioning has not been sufficiently researched; therefore, there are no known approaches for automated zone delimitation. This study proposes a new method based on a discrete version of the adaptive additively weighted Voronoi diagram that makes it possible to partition a two-dimensional space into zones of specific sizes, taking both the position and the weight of each seed into account. The method consists of repeatedly solving a traditional additively weighted Voronoi diagram, so that each seed's weight is updated at every iteration. The zones are geographically connected using a metric based on the shortest path. Tests conducted on the extensive farming system of three municipalities in Castile-La Mancha (Spain) have established that the proposed heuristic procedure is valid for solving this type of partitioning problem. Nevertheless, these tests confirmed that the given seed position determines the spatial configuration the method must solve and this may have a great impact on the resulting partition.  相似文献   

12.
A Monte Carlo approach is used to evaluate the uncertainty caused by incorporating Post Office Box (PO Box) addresses in point‐cluster detection for an environmental‐health study. Placing PO Box addresses at the centroids of postcode polygons in conventional geocoding can introduce significant error into a cluster analysis of the point data generated from them. In the restricted Monte Carlo method I presented in this paper, an address that cannot be matched to a precise location is assigned a random location within the smallest polygon believed to contain that address. These random locations are then combined with the locations of precisely matched addresses, and the resulting dataset is used for performing cluster analysis. After repeating this randomization‐and‐analysis process many times, one can use the variance in the calculated cluster evaluation statistics to estimate the uncertainty caused by the addresses that cannot be precisely matched. This method maximizes the use of the available spatial information, while also providing a quantitative estimate of the uncertainty in that utilization. The method is applied to lung‐cancer data from Grafton County, New Hampshire, USA, in which the PO Box addresses account for more than half of the address dataset. The results show that less than 50% of the detected cluster area can be considered to have high certainty.  相似文献   

13.
孟凡超  郭军  李明财  张雷  张瑞雪 《地理科学》2020,40(10):1753-1762
基于自动气象站实测资料，通过模拟天津市办公建筑逐时供暖负荷，重点分析了极端低温过程中城市热岛对建筑小时供暖负荷的影响，以期为精细化供暖调控和节能设计提供参考。结果表明：2009—2017年城市和乡村办公建筑供暖负荷均呈减少趋势，城市供暖负荷较乡村平均每年减少7.46%。城市热岛强度(Urban heat island intensity, UHII)每上升1℃，城市办公建筑年供暖负荷较乡村减少2.19 kWh/m2，即热岛强度的增加使城市办公建筑供暖需求有所减少，有利于城市建筑的供暖节能。以2016年1月21~25日典型极端低温过程为例，研究发现，低温过程中城乡小时供暖负荷明显增加，较低温前和低温后增加约10%~20%。受大尺度天气过程影响，低温过程中城乡气温差异变小，UHII减弱。低温前和低温后城市供暖负荷较乡村减少约6%~8%，而低温过程中城市较乡村仅减少约3%；另外，在低温过程中，北京时间07:00~19:00的高负荷时段城乡供暖负荷差异不明显，这些结果表明低温过程中城市热岛对办公建筑供暖负荷的影响不大。  相似文献   

14.
北京城市形态的分形集聚特征及其实践意义   总被引：26，自引：6，他引：26  
姜世国  周一星 《地理研究》2006,25(2):204-212
基于1984、1999年Landsat TM遥感图像,根据分形理论,用半径法研究了北京城市形态,发现北京城市具有分形性质。北京市建设用地从中心向外扩散的集聚分形结构存在明显的标度区转折现象,其中第一标度区是能够揭示北京城市形态演化特点的有效标度区。1984、1999年半径维数的数值变化反映了建设用地密度集聚扩散的不同特点。本文根据集聚分形的标度区建立了一种新的城市范围定义,这种定义可以减少通常定义中的主观因素和不可比因素,标度区大小具有一定的理论意义。  相似文献   

15.
One feature discovered in the study of complex networks is community structure, in which vertices are gathered into several groups where more edges exist within groups than between groups. Many approaches have been developed for identifying communities; these approaches essentially segment networks based on topological structure or the attribute similarity of vertices, while few approaches consider the spatial character of the networks. Many complex networks are spatially constrained such that the vertices and edges are embedded in space. In geographical space, nearer objects are more related than distant objects. Thus, the relations among vertices are defined not only by the links connecting them but also by the distance between them. In this article, we propose a geo-distance-based method of detecting communities in spatially constrained networks to identify communities that are both highly topologically connected and spatially clustered. The algorithm is based on the fast modularity maximisation (CNM) algorithm. First, we modify the modularity to geo-modularity Qgeo by introducing an edge weight that is the inverse of the geographic distance to the power of n. Then, we propose the concept of a spatial clustering coefficient as a measure of clustering of the network to determine the power value n of the distance. The algorithm is tested with China air transport network and BrightKite social network data-sets. The segmentation of the China air transport network is similar to the seven economic regions of China. The segmentation of the BrightKite social network shows the regionality of social groups and identifies the dynamic social groups that reflect users’ location changes. The algorithm is useful in exploring the interaction and clustering properties of geographical phenomena and providing timely location-based services for a group of people.  相似文献   

16.
Complex regions are composed of a finite number of simple regions, and are always defined by hierarchical representation methods. This article focuses on a unified method for computing n-intersection-based binary topological relations between complex regions based on hierarchical characteristics, using known topological relations between simple regions. The hierarchical representation of complex regions is defined as the recursive process of region decomposition using a context-free grammar. To distinguish multiple components of a region and whether the interior of a hole is a part of the inner exterior or the outer exterior, three region operators are proposed to describe the configuration of a region represented as a formal expression. Then, three corresponding 25-intersection (25I) based Boolean matrix operators are proposed to compute topological relations based on the relationships between decomposed regions. Herein, the invalid conditions of the operators are verified in detail, and the invalidities can be eliminated by either applying our definition of complex regions or with the inclusion of additional information. The proposed 25I-based operators, as shown in our cases, can be used as a ‘bridge’ to link different n-intersection models, and as a useful computation tool for analyzing topological relations between regions with specific configurations.  相似文献   

17.
以大连市中山区2003年、2013年城市三维建筑数据为基础,选取三维景观指标,运用ArcGIS空间分析方法从多个角度来研究城市10年间建筑景观格局时空分异特征。结果表明：① 大连市中山区建筑加权平均高度和体积分别增加7.87 m、277.25×104 m3;地块覆盖率减少了16.27%,容积率增加了20.67%,反映出城市水平和垂直空间分别呈收缩、扩展的态势。② 中山区城市天际线起伏差异明显,东—西方向呈逐渐增高的趋势,南—北方向呈“北部高峰,中部和南部平缓”格局。城市高层建筑主要集中于城市的西北部,且2013年建筑最高点中心裕景比2003年宏进大厦高140 m。③ 建筑覆盖率和容积率在空间分布上差异明显,低和极低覆盖率与容积率地块所占比例大,分别增加了8.3%、-4.33%;高和极高覆盖率与容积率地块所占比例少,且集中分布在青泥洼桥和人民路街道。④ 2003年超高层建筑在空间分布上呈“聚集—离散”状态,即在距离660 m尺度范围内呈聚集状态,大于660 m时呈离散分布,其他三种建筑类型在空间上都呈一定的聚集分布状态;2013年4种不同类型建筑在空间分布上都呈现一定的聚集分布状态,聚集程度为：超高层建筑>低层建筑>多层建筑>高层建筑。  相似文献   

18.
In this paper, conformal geometric algebra (CGA) is introduced to construct a Delaunay–Triangulated Irregular Network (DTIN) intersection for change detection with 3D vector data. A multivector-based representation model is first constructed to unify the representation and organization of the multidimensional objects of DTIN. The intersection relations between DTINs are obtained using the meet operator with a sphere-tree index. The change of area/volume between objects at different times can then be extracted by topological reconstruction. This method has been tested with the Antarctica ice change simulation data. The characteristics and efficiency of our method are compared with those of the Möller method as well as those from the Guigue–Devillers method. The comparison shows that this new method produces five times less redundant segments for DTIN intersection. The computational complexity of the new method is comparable to Möller’s and that of Guigue–Devillers methods. In addition, our method can be easily implemented in a parallel computation environment as shown in our case study. The new method not only realizes the unified expression of multidimensional objects with DTIN but also achieves the unification of geometry and topology in change detection. Our method can also serve as an effective candidate method for universal vector data change detection.  相似文献   

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20.
As an approach to understand how diurnal and seasonal plant water potentials (Ψ) are related to soil water-content and evaporative demand components, the responses of six thornscrub shrubs species (Havardia pallens, Acacia rigidula, Eysenhardtia texana, Diospyros texana, Randia rhagocarpa, and Bernardia myricaefolia) of the north-eastern region of Mexico to drought stress were investigated during the course of 1 year. All study species showed the typical diurnal pattern of variation in Ψ. That is, Ψ decreased gradually from predawn (Ψpd) maximal values to reach minima at midday (Ψmd) and began to recover in the late afternoon. On a diurnal basis and with adequate soil water-content (>0.20 kg kg−1), diurnal Ψ values differed among shrub species and were negatively and significantly (p<0.001) correlated with air temperature (r=−0.741 to −0.883) and vapor pressure deficit (r=−0.750 to −0.817); in contrast, a positive and significant (p<0.001) relationship was found to exist with relative humidity (r=0.758–0.842). On a seasonal basis, during the wettest period (soil water-content>0.20 kg kg−1), higher Ψpd (−0.10 MPa) and Ψmd (−1.16 MPa) values were observed in R. rhagocarpa, whereas lower figures (−0.26 and −2.73 MPa, respectively) were detected in A. rigidula. On the other hand, during the driest period (soil water-content<0.15 kg kg−1), Ψpd and Ψmd values were below −7.3 MPa; i.e. when shrubs species faced severe water deficit. Soil water-content at different soil layers, monthly mean relative humidity and monthly precipitation were significantly correlated with both Ψpd (r=0.538–0.953; p<0.01) and Ψmd (r=0.431–0.906; p<0.05). Average soil water-content in the 0–50 cm soil depth profile explained between 70% and 87% of the variation in Ψpd. Results have shown that when gravimetric soil water-content values were above 0.15 kg kg−1, Ψpd values were high and constant; below this threshold value, Ψ declined gradually. Among all shrub species, A. rigidula appeared to be the most drought tolerant of the six species since during dry periods it tends to sustain significantly higher Ψpd in relation to B. myricaefolia. The remaining species showed an intermediate pattern. It is concluded that the ability of shrub species to cope with drought stress depends on the pattern of water uptake and the extent to control water loss through the transpirational flux.  相似文献   

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