共查询到20条相似文献，搜索用时 15 毫秒
1.
Hiroyuki Usui 《Journal of Geographical Systems》2018,20(4):387-412
The structure of road networks has been investigated in accordance with the development of GIScience. By classifying road networks into wide and narrow ones, we can define the route as the path from the route’s origin (also called the root) on a wide road network to a narrow road segment which consists of the sequence of narrow road segments arranged by ascending order of the number of steps of adjacency to its root. The length of the route can be defined with the following geometric and topological terms: the route distance, measuring the length along the route and the depth, counting the number of road segments on the route. The depth plays the important role of being a substitute for the route distance in modelling road networks as a planar graph. Since road networks clearly exhibit irregular patterns and road segment lengths are non-uniform, it is considered appropriate to adopt a stochastic approach rather than a deterministic one to analyse the route distance. However, the relationship between the route distance and its depth has not been sufficiently investigated stochastically. Therefore, the research question is how can we estimate the route distance from its depth? Based on an empirical study in the Tokyo metropolitan region, it was found that (1) the statistical distribution of the route distance can be formulated as an Erlang distribution whose parameters are its depth and the inverse of the mean length of narrow road segments, and (2) this length is constant and close to 40 m. Therefore, we can estimate the route distance from only one parameter, the depth. Also, as a practical application, accessibility to the kth depth link in terms of firefighting was evaluated because the maximum length of the extension of fire hoses is approximately 200 m. It was found that (1) even if k?≤?5, the probability that the route distance to the kth depth link is equal to or longer than 200 m ranges from 0 to 0.45; and (2) if k?≥?8, the probability is approximately 1. These indicate the limitation of the deterministic approach because, on the basis of complete grid patterns (with intervals of 40 m between intersections), k?=?5 corresponds to a distance of 200 m from wide road networks and the route to the 5th depth link can be covered with fire hoses. Moreover, it was found that the connectivity of wide road networks is higher than that of narrow ones in terms of the smaller ratio of cul-de-sacs and the larger ratio of four-way intersections. These answers contribute substantially not only to constructing a science of cities that provides a simple model and specifies the most important parameter, but also to our understanding of the structure of narrow road networks within several hundred metres of wide road networks. 相似文献
2.
Shawky MANSOUR 《地球空间信息科学学报》2016,19(1):26-38
Much attention has been given to address public health policy in Saudi Arabia, particularly for the management, quality, and coverage issues. However, assessment of spatial patterns, distribution, and provision of public health services has been neglected. This paper analyzes the availability and accessibility of public health facilities across Riyadh Governorate, Saudi Arabia at the subnational level. Spatial and attribute data of public health facilities potentially have been analyzed using GIS to produce accurate measure of accessibility. The spatial pattern of service distribution was examined using average nearest neighbor. Distances from demand points (populations) to providers (facilities) were calculated for each district using near analysis. In addition, the ratios of public health facility to population were calculated to identify underserved and overserved areas. The findings clearly indicate that the spatial pattern of the distribution of public health facilities was significantly clustered (p value < 0.001) with Z-score of ?10.9. Several districts within the central parts of the governorate were identified as having a higher density of facilities, while most of districts that are located in the marginal parts exhibit very low density of health facilities. Overall, there was a considerable variation in the average distance from district centroids to health facilities. Substantially, less than half of the population (45.4%) living in 61 districts has access to public health facility within less than 1-km distance. In contrast, the greatest increase in distances was observed for 6% of population living in 38 districts. People that live in such districts need to travel long distances for public health care. The output of this analysis can assist policy-makers and authorities of Riyadh Governorate in planning public health delivery. 相似文献
3.
路网环境下的k最近邻查询方法在地理信息系统、智慧城市、数据挖掘、医疗营救和物流配送等领域都有着较为重要的作用,已有路网环境下的最近邻查询方法无法直接解决查询对象为点而数据对象为点和线段混合的复杂数据的近邻查询问题,为了弥补已有方法的不足,提出了路网环境下混合复杂数据的最近邻查询算法。将查询过程分为预处理、数据集约减和数据集精炼3个部分,并与3种对比算法进行对比实验,研究了测试数据对象的数量、路网规模的大小对中央处理器运行时间以及输入/输出代价的影响。结果表明,所提算法能有效地处理路网环境下混合数据的最近邻查询问题。 相似文献
4.
GIS与Voronoi多边形在医疗服务设施地理可达性分析中的应用 总被引：5，自引：0，他引：5
王远飞 《测绘与空间地理信息》2006,29(3):77-80
地理可达性是研究评价各种服务设施布局及其服务域的重要指标之一,空间距离、交通便捷性、出行成本等是可达性测度的重要因子。由于医疗设施等公共设施通常以服务的公平性和覆盖性为目标,因此可定义居民点到最邻近医院的距离为地理可达性的测度。在此基础上,作者提出了基于GIS与Voronoi多边形的地理可达性计算方法。这一方法不仅将地理可达性分析中的空间点对之间的距离计算简化为空间查询,方便了GIS应用,而且计算的Voronoi多边形在本质上就是最邻近意义上医院的服务域,即服务域内各居民点到该医院的距离就是最邻近距离。此外结合人口分布等属性数据,还可深入分析各医院的服务承载力,本方法为医疗设施等公共服务设施的规划决策提供了重要的工具。 相似文献
5.
Distances between demand points and potential sites for implementing facilities are essential inputs to location-allocation
models. Computing actual road distances for a given problem can be quite burdensome since it involves digitalizing a network,
while approximating these distances by l
p
-norms, using for instance a geographical information system, is much easier. We may then wonder how sensitive the solutions
of a location-allocation model are to the choice of a particular metric. In this paper, simulations are performed on a lattice
of 225 points using the k-median problem. Systematic changes in p and in the orientation of the orthogonal reference axes are used. Results suggest that the solutions of the k-median are rather insensitive to the specification of the l
p
-norm.
Received: 12 October 1998/Accepted: 17 September 1999 相似文献
6.
Richard A. Snay 《Journal of Geodesy》1990,64(1):1-27
The North American Datum of 1983 (NAD 83) provides horizontal coordinates for more than 250,000 geodetic stations. These coordinates were derived by a least squares
adjustment of existing terrestrial and space-based geodetic data. For pairs of first order stations with interstation distances
between 10km and 100km, therms discrepancy between distances derived fromNAD 83 coordinates and distances derived from independentGPS data may be suitably approximated by the empirical rulee=0.008 K0.7 where e denotes therms discrepancy in meters and K denotes interstation distance in kilometers. For the same station pairs, therms discrepancy in azimuth may be approximated by the empirical rule e=0.020 K0.5. Similar formulas characterize therms discrepancies for pairs involving second and third order stations. Distance and orientation accuracies, moreover, are well
within adopted standards. While these expressions indicate that the magnitudes of relative positional accuracies depend on
station order, absolute positional accuracies are similar in magnitude for first, second, and third order stations. Adjustment
residuals reveal a few local problems with theNAD 83 coordinates and with the weights assigned to certain classes of observations. 相似文献
7.
校车站点布局问题是一种典型的设施选址问题。大多数设施选址问题均属于区域选址,将设施选址限定在一定空间范围内,其方法并不适用于需要将位置固定在道路上的校车站点布局问题。因此,为保证生成的站点分布在路网上,且学生到站点的步行距离较短,提出了一种改进的K-means聚类算法,以一定范围内密度最大的点为初始类中心,在逐次迭代中将类中心投影到路网上,进而聚类得到校车站点。与传统的利用最大最小距离法的改进方式进行对比发现,在相同的站点间最小间距下,基于密度法改进初始类中心的K-means算法使得学生到车站总步行距离较短,且迭代次数明显减少。该方法还可适用于超市班车站点选址、物流配送点选址等问题。 相似文献
8.
Peter M. Atkinson 《International Journal of Applied Earth Observation and Geoinformation》2004,5(4):277-291
A simple approach for incorporating a spatial weighting into a supervised classifier for remote sensing applications is presented. The classifier modifies the feature-space distance-based metric with a spatial weighting. This is facilitated by the use of a non-parametric (k-nearest neighbour, k-NN) classifier in which the spatial location of each pixel in the training data set is known and available for analysis. A remotely sensed image was simulated using a combined Boolean and geostatistical unconditional simulation approach. This simulated image comprised four wavebands and represented three classes: Managed Grassland, Woodland and Rough Grassland. This image was then used to evaluate the spatially weighted classifier. The latter resulted in modest increase in the accuracy of classification over the original k-NN approach. Two spatial distance metrics were evaluated: the non-centred covariance and a simple inverse distance weighting. The inverse distance weighting resulted in the greatest increase in accuracy in this case. 相似文献
9.
In the real world, there are many kinds of phenomena that are represented by points on a network, such as traffic accidents
on a street network. To analyse these phenomena, the basic point pattern methods (i.e. the nearest neighbour distance method,
the quadrat method, the K-function method and the clumping method) defined on a plane (referred to as the planar basic point pattern methods) are extended to the basic point pattern methods on a network (referred to as the network basic point pattern methods). However, like the planar basic point pattern methods, the network basic point pattern methods assume a uniform network
and this assumption is hard to accept when analysing actual phenomena. To overcome this limitation, this paper formulates
a transformation, called the uniform network transformation, that transforms a non-uniform network into a uniform network. This transformation provides a simple procedure for analysing
point patterns on non-uniform networks: first, a given non-uniform network is transformed into a uniform network; second,
the network basic point pattern methods (which assume a uniform network) are applied to this transformed uniform network.
No modification to the network basic point pattern methods is necessary. The paper also shows an actual application of this
transformation to traffic accidents in Chosei, Japan. 相似文献
10.
Network Density Estimation: A GIS Approach for Analysing Point Patterns in a Network Space 总被引：4，自引：0，他引：4
Giuseppe Borruso 《Transactions in GIS》2008,12(3):377-402
Human activities and more generally the phenomena related to human behaviour take place in a network‐constrained subset of the geographical space. These phenomena can be expressed as locations having their positions configured by a road network, as address points with street numbers. Although these events are considered as points on a network, point pattern analysis and the techniques implemented in a GIS environment generally consider events as taking place in a uniform space, with distance expressed as Euclidean and over a homogeneous and isotropic space. Network‐spatial analysis has developed as a research agenda where the attention is drawn towards point pattern analytical techniques applied to a space constrained by a road network. Little attention has been put on first order properties of a point pattern (i.e. density) in a network space, while mainly second order analysis such as nearest neighbour and K‐functions have been implemented for network configurations of the geographical space. In this article, a method for examining clusters of human‐related events on a network, called Network Density Estimation (NDE), is implemented using spatial statistical tools and GIS packages. The method is presented and compared to conventional first order spatial analytical techniques such as Kernel Density Estimation (KDE). Network Density Estimation is tested using the locations of a sample of central, urban activities associated with bank and insurance company branches in the central areas of two midsize European cities, Trieste (Italy) and Swindon (UK). 相似文献
11.
One of the simplest location models in terms of its constraint structure in location‐allocation modeling is the location set‐covering problem (LSCP). Although there have been a variety of geographic applications of the set‐covering problem (SCP), the use of the SCP as a facility location model is one of the most common. In the early applications of the LSCP, both potential facility sites as well as demand were represented by points discretely located in geographic space. The advent of geographic information systems (GIS), however, has made possible a greater range of object representations that can reduce representation error. The purpose of this article is to outline a methodology using GIS and K = 3 central place lattices to solve the LSCP when demand is continuously distributed over a bounded area and potential facility sites have not been defined a priori. Although, demand is assumed to exist over an area, it is shown how area coverage can be accomplished by the coverage of a point pattern. Potential facility site distributions based on spacings that are powers of one‐third the coverage distance are also shown to provide more efficient coverage than arbitrarily chosen spacings. Using GIS to make interactive adjustments to an incomplete coverage also provides an efficient alternative to smaller spacings between potential facility sites for reducing the number of facilities necessary for complete coverage. 相似文献
12.
M. E. O’Kelly 《Journal of Geographical Systems》2009,11(3):227-241
The minimax hub location problem sites a facility to minimize the maximum weighted interaction cost between pairs of fixed nodes. In this paper, distances are represented by a rectilinear norm and may be suited to factory layout or street
network problems. The problem is already well known (in 2-D) as the round trip location problem and is extended to 3-D in
this paper. One rationale for the solution method is based on an extension of the geometric arguments used to solve the minimax
single facility location problem. Suppose a budget is provided for interactions, and that each interaction must be accomplished
for no more than this cost. The algorithm uses a bi-section search for the feasible budget until it finds the expenditure
needed to provide for these flows. The extension in the present paper is that the nodes are permitted to be on different layers
(levels). This 3-D version of the problem appears to be a new variant of the hub model. The models and solution techniques
developed in the paper are illustrated using a small 55 node problem. Because of a relatively efficient implementation of
the bi-section search, the algorithm in 2-D and 3-D is also applied successfully to a 550 node problem.
相似文献
| M. E. O’KellyEmail: |
13.
针对位置指纹匹配算法计算量大导致室内定位精度不高的问题,提出了一种基于接收信号强度指示(RSSI)的联合算法. 该算法以K近邻位置指纹匹配算法为基础算法,加入三角定位辅助算法,首先进行三角定位得出参考区域,再进行位置指纹匹配进行精准定位,有效地提高了定位精度. 使用Android Studio基于Java语言开发了一款集Wi-Fi位置指纹采集与在线定位一体化的软件,并在试验场地进行测试.实验结果表明:该算法定位精度在二维平面内达到 1～3 m,较单一算法定位精度有所提高. 相似文献
14.
Previous research has shown that forest roads are an important feature in many landscapes and have significant effects on wildfire ignition and cessation. However, forest road effects on burn severity have not been studied at the landscape level. Therefore, the overarching goal of our study is to identify the influences of road edge effects on the spatial patterns of burn severity. We analyzed six fires within the Okanogan–Wenatchee National Forest on the eastern slope of the Cascades mountain range of central Washington.We generated two categories for assessing road variables: (1) Primary Road Effect Zone (area within 150 m of the nearest road) and (2) Secondary Road Effect Zone (area from 150 m to 300 m to the nearest road). A regular sampling grid including one out of every 9 cells was created for each fire.These grids were intersected with burn severity data in the form of the Relative Differenced Normalized Burn Ratio (RdNBR), road distance category, stream distance, elevation, slope, terrain shape index, heat load index, canopy cover, and fuel type. We fit spatial regression models with RdNBR as the dependent variable.We found that high burn severity is less likely to occur in the Primary Road Effect Zone for most fires, although one fire exhibited the opposite relationship. Forest road edge effects were hypothesized to be an important determinant of burn severity because fragmentation created by roads alters the roadside fuel profile and environment and because road corridors create barriers to fire spread. Recognizing roadside effects on burn severity patterns highlights the need for further study of the range of effects that roads have on fuels and the fire environment and the potential for incorporating road effects into landscape-level assessments of fire risk. 相似文献
15.
Matching multi-scale road networks in the same area is the first step in merging two road networks or updating one based upon the other. The quality of the merge or update depends greatly on the matching accuracy of the two road networks. We propose an improved probabilistic relaxation method, considering both local and global optimizations for matching multi-scale of road networks. The aim is to achieve local optimization, as well as to address the identification of the M:N matching pattern by means of inserting virtual nodes to achieve global optimization effects. Then, by adding two attribute-related evaluation indicators, we developed four evaluation indicators to evaluate the matching accuracy, considering both geographic and attribute information. This paper also provides instructions on how to identify the proper buffer threshold during matching procedures. Extensive experiments were conducted to compare the proposed method with the traditional approach. The results indicate that: (1) the overall matching accuracy of each evaluation indicator exceeds 90%; (2) the overall matching accuracy increases by 6–12% after an M:N matching pattern is added, and by 4–6% following the addition of topology indicators; and (3) the proper buffer threshold is about twice the average value of the closest distance from all nodes. 相似文献
16.
Knox检验是一种常用的城市犯罪时空交互模式分析方法,但其阈值需要人为指定,这种主观的阈值确定方法存在一定随意性,因此需探索更为合理的阈值确定方法。提出利用点对平均最邻近距离作为Knox检验空间阈值的确定方法,并通过城市入室盗窃、盗窃电动车和扒窃3类事件进行实验验证。结果表明,与常见的几种阈值确定方法相比,所提方法检测出了最大数量的显著性交互事件对数,能更加充分地了解事件的真实时空交互模式,为基于Knox检验的事件时空聚集模式分析提供了一种有效的空间阈值确定手段。 相似文献
17.
The p‐median problem (PMP) is one of the most applied location problems in urban and regional planning. As an NP‐hard problem, the PMP remains challenging to solve optimally, especially for large‐sized problems. A number of heuristics have been developed to obtain PMP solutions in a fast manner. Among the heuristics, the Teitz and Bart (TB) algorithm has been found effective for finding high‐quality solutions. In this article, we present a spatial‐knowledge‐enhanced Teitz and Bart (STB) heuristic method for solving PMPs. The STB heuristic prioritizes candidate facility sites to be examined in the solution set based on the spatial distribution of demand and service provision. Tests based on a range of PMPs demonstrate the effectiveness of the STB heuristic. This new algorithm can be incorporated into current commercial GIS packages to solve a wide range of location‐allocation problems. 相似文献
18.
Clustering is one of the most prevalent and important data mining algorithms ever developed. Currently, most clustering methods are divided into distance-based and density-based. In 2014, the fast search and find of density peaks clustering method was proposed, which is simple and effective and has been extensively applied in several research domains. However, the original version requires manually assigning a cut-off distance and selecting core points. Therefore, this article improves the density peak clustering method from two aspects. First, the Gaussian kernel is substituted with a k-nearest neighbors method to calculate local density. This is important as compared with selecting a cut-off distance, calculating the k-value is easier. Second, the core points are automatically selected, unlike the original method that manually selects the core points regarding local density and distance distribution. Given that users' selection influences the clustering result, the proposed automatic core point selection strategy overcomes the human interference problem. Additionally, in the clustering process, the proposed method reduces the influence of manually assigned parameters. 相似文献
19.
提出了两种基于圆形的单幅图像平面几何量测方法。第一种算法首先计算出与待测对象平行的直径,然后获得圆形所在平面上任意两点之间的距离。受待测线段位置、方向等影响,量测结果的精度各向差异大。第二种算法首先求取圆形的外接正方形,将问题转化为包含正方形的平面距离量测。模拟图像与真实图像的测试结果表明,第二种算法的量测精度更具有稳定性。 相似文献
20.
海岸带作为海洋、陆地和大气共同作用的地带，其地物混杂度大，变化频繁，单纯利用光谱特征分类难以取得理想的精度。
但海岸带地物滨临水体，而水体与地物存在巨大光谱差异，易于识别。据此，本文尝试提出一种简单的加入空间关系的遥感图像分类
方法，即，先准确识别出海水类，然后统计非海水类的每一个像元到最近海水的空间距离。由于不同的海岸带地类距离海水的空间距
离有其自身的特点，因此，利用这一距离信息辅助分类能提高分类精度，尤其是针对那些光谱特征相近而距离相差较大的地类。 相似文献