共查询到20条相似文献，搜索用时 62 毫秒
1.
Bart Kuijpers Walied Othman 《International journal of geographical information science》2017,31(9):1722-1748
Space-time prisms envelop all spatio-temporal locations that moving objects may have visited between two of their known spatio-temporal locations, given a bound on their travel speed. In this context, the known locations are often the result of observations or measurements, and they are called ‘anchor points’. The classic space-time prism, in isotropic two-dimensional space, as well as in transportation networks, assumes that the measurements of these anchor points are exact. Whereas, in many applications, we can assume that time can be measured fairly precisely, this assumption is unrealistic for the spatial components of measured locations (we think of Global Positioning System (GPS) errors, for instance). In this paper, we extend the classical prism from anchor points to circular ‘anchor regions’ that capture the uncertainty or error on their measurement. We define the notion of a space-time prism with uncertain anchor points, called uncertain prism, for short. We study the geometry of uncertain prisms in an arbitrary metric space to make this concept as widely applicable as possible. We also focus on the rims of uncertain space-time prisms, which demarcate the area that a moving object can have visited between two anchor regions (given some local speed limitations). 相似文献
2.
Ying Song 《International journal of geographical information science》2014,28(1):104-125
The space-time prism is key concept in time geography and moving objects databases; it demarcates all locations that a mobile object can occupy given anchor locations and times and a maximum velocity for travel. Although the prism’s spatial and temporal extent is widely applied as a measure of accessibility and object locational uncertainty, until recently little attention has been paid to the properties of the prism interior such as the probabilities of the object visiting different locations within the prism. Better understanding of the visit probability distribution within the prism can improve theoretical understanding as well as refine the prism as a practical measure of space-time accessibility and object uncertainty. This paper presents two methods for modeling the distribution of visit probabilities within planar space-time prisms: (1) a directed Random Walk method for discrete space and time, and (2) a truncated Brownian Bridges method for continuous space and time. We illustrate these methods and demonstrate the effect of prism and mobility parameters on the visit probability distributions within the prism. 相似文献
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Bart Kuijpers 《International journal of geographical information science》2013,27(9):1095-1117
Moving objects produce trajectories, which are typically observed in a finite sample of time‐stamped locations. Between sample points, we are uncertain about the moving objects's location. When we assume extra information about an object, for instance, a (possibly location‐dependent) speed limit, we can use space–time prisms to model the uncertainty of an object's location. Until now, space–time prisms have been studied for unconstrained movement in the 2D plane. In this paper, we study space–time prisms for objects that are constrained to travel on a road network. Movement on a road network can be viewed as essentially one‐dimensional. We describe the geometry of a space–time prism on a road network and give an algorithm to compute and visualize space–time prisms. For experiments and illustration, we have implemented this algorithm in MATHEMATICA. Furthermore, we study the alibi query, which asks whether two moving objects could have possibly met or not. This comes down to deciding if the chains of space–time prisms produced by these moving objects intersect. We give an efficient algorithm to answer the alibi query for moving objects on a road network. This algorithm also determines where and when two moving objects may have met. 相似文献
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Stephan Winter Zhang-Cai Yin 《International journal of geographical information science》2013,27(9):1349-1365
This article studies probabilistic time geography for space–time prisms, that is, for situations where observers know the location of an agent at one time and then again at another time. In the intervening period, the agent would have moved freely, according to its time budget. The article demonstrates that the probability of finding the agent somewhere in the space–time prism is not equally distributed, so any attempt of a quantitative time geographic analysis must consider the actual probability distribution. This article develops, implements, and demonstrates this distribution. A preceding article introduced probabilistic time geography for space–time cones. With cones and prisms, the elementary space–time volumes of time geography are provided. 相似文献
7.
Mei-Po Kwan 《The Professional geographer》1999,51(2):210-227
Conventional accessibility measures based on the notion of locational proximity ignore the role of complex travel behavior and space–time constraints in determining individual accessibility. As these factors are especially significant in women's everyday lives, all conventional accessibility measures suffer from an inherent “gender bias.” This study conceptualizes individual accessibility as space–time feasibility and provides formulations of accessibility measures based on the space–time prism construct. Using a subsample of European Americans from a travel diary data set collected in Franklin County, Ohio, space–time accessibility measures are implemented with a network-based GIS method. Results of the study indicate that women have lower levels of individual access to urban opportunities when compared to men, although there is no difference in the types of opportunities and areas they can reach given their space–time constraints. Further, individual accessibility has no relationship with the length of the commute trip, suggesting that the journey to work may not be an appropriate measure of job access. 相似文献
8.
Bi Yu Chen Donggen Wang Shih-Lung Shaw Hui-Ping Chen 《International journal of geographical information science》2017,31(4):783-804
Travel time uncertainty has significant impacts on individual activity-travel scheduling, but at present these impacts have not been considered in most accessibility studies. In this paper, an accessibility evaluation framework is proposed for urban areas with uncertain travel times. A reliable space-time service region (RSTR) model is introduced to represent the space-time service region of a facility under travel time uncertainty. Based on the RSTR model, four reliable place-based accessibility measures are proposed to evaluate accessibility to urban services by incorporating the effects of travel time reliability. To demonstrate the applicability of the proposed framework, a case study using large-scale taxi tracking data is carried out. The results of the case study indicate that the proposed accessibility measures can evaluate large-scale place-based accessibility well in urban areas with uncertain travel times. Conventional place-based accessibility indicators ignoring travel time reliability can significantly overestimate the accessibility to urban services. 相似文献
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Feixiong Liao 《International journal of geographical information science》2019,33(5):900-921
Space–time prism (STP), which envelops the spatial and temporal opportunities for travel and activity participation within a time frame, is a fundamental concept in time geography. Despite many variants, STPs have been mostly modeled for one flexible activity between two anchor points. This study proposes a systemic approach to construct the STP bounds of activity programs that usually include various possible realizations of activity chains. To that effect, multi-state supernetworks are applied to represent the relevant path sets of multi-activity travel patterns. A goal-directed search method in multi-state supernetworks is developed to delineate the potential space–time path areas satisfying the space–time constraints. Particularly, the approximate lower and upper STP bounds are obtained by manipulating the goal-directed search procedure utilizing landmark-based triangular inequalities and spatial characteristics. The suggested approach can in an efficient fashion find the activity state dependent bounds of STP and potential path area. The formalism of goal-directed search through multi-state supernetworks addresses the fundamental shift from constructing STPs for single flexible activities to activity programs of flexible activity chains. 相似文献
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Rebecca W. Loraamm 《International journal of geographical information science》2020,34(8):1607-1627
ABSTRACT Animal movement is a dynamic spatio-temporal process. While trajectory data reflect the instantaneous animal position in space and time, other factors influence movement decisions between these observed positions. While some methods incorporate environmental (habitat) context into their understanding of the animal movement process, it is often captured in terms of simple parameters or weights influencing model results; primary behavioral data are not used directly to inform these models. Here, a new space-time constrained agent-based model is introduced, capable of producing ordered, behaviorally informed animal potential paths between observed space-time anchors. Potential paths generated by this approach incorporate both observed animal behavior and classical space-time constraints, and are used to construct associated visit probability distributions. Additionally, the notion of a behavioral space-time path is introduced, a variant of the space-time path based on the results of behaviorally aware animal movement simulation. The results of this approach demonstrate a means to better understand the varied movement opportunities within space-time prisms from an animal behavior perspective. From a spatial ecology perspective, not only is the environmental context considered, but the animal’s choice of transition and movement magnitude between contexts is modeled. This approach provides insight into the complex sequence of behaviorally informed actions driving animal movement decision-making. 相似文献
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Yingjie Hu Krzysztof Janowicz Yuqi Chen 《International journal of geographical information science》2016,30(6):1228-1249
Recent years have witnessed a large increase in the amount of information available from the Web and many other sources. Such an information deluge presents a challenge for individuals who have to identify useful information items to complete particular tasks in hand. Information value theory (IVT) from economics and artificial intelligence has provided some guidance on this issue. However, existing IVT studies often focus on monetary values, while ignoring the spatiotemporal properties which can play important roles in everyday tasks. In this paper, we propose a theoretical framework for task-oriented information value measurement. This framework integrates IVT with the space-time prism from time geography and measures the value of information based on its impact on an individual’s space-time prisms and its capability of improving task planning. We develop and formalize this framework by extending the utility function from space-time accessibility studies and elaborate it using a simplified example from time geography. We conduct a simulation on a real-world transportation network using the proposed framework. Our research could be applied to improving information display on small-screen mobile devices (e.g., smartwatches) by assigning priorities to different information items. 相似文献
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Gender differences in space-time constraints 总被引：7，自引：0，他引：7
Mei-Po Kwan 《Area》2000,32(2):145-156
Summary This study explores gender differences in space-time constraints and their impact on women's and men's activity-travel patterns from a time-geographic perspective. Using a travel diary data set collected in Columbus, Ohio (USA), the time-budget and fixity constraints of three population subgroups are examined. This paper concludes that space-time constraints have a significant impact on individual's activity-travel patterns. 相似文献
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In geostatistics, most stochastic algorithm for simulation of categorical variables such as facies or rock types require a
conditional probability distribution. The multivariate probability distribution of all the grouped locations including the
unsampled location permits calculation of the conditional probability directly based on its definition. In this article, the
iterative proportion fitting (IPF) algorithm is implemented to infer this multivariate probability. Using the IPF algorithm,
the multivariate probability is obtained by iterative modification to an initial estimated multivariate probability using
lower order bivariate probabilities as constraints. The imposed bivariate marginal probabilities are inferred from profiles
along drill holes or wells. In the IPF process, a sparse matrix is used to calculate the marginal probabilities from the multivariate
probability, which makes the iterative fitting more tractable and practical. This algorithm can be extended to higher order
marginal probability constraints as used in multiple point statistics. The theoretical framework is developed and illustrated
with estimation and simulation example. 相似文献
14.
Dana Tomlin 《International journal of geographical information science》2013,27(9):1391-1413
To calculate the minimum cost of travel to each location within a geographical area from a specified set of locations, most geographic information systems represent that area as a rectangular grid of discrete cells, each indicating the cost of traversing that cell's particular location. These increments of cost are then accumulated by proceeding from cell to adjacent cell in a manner that resembles the propagation of waves. Because this propagation is limited to the eight directions associated with each cell's eight neighbors, however, it is often misdirected, and travel costs are therefore often overestimated. This article discusses the context, precedent, design, implementation, performance, and implications of a new algorithm that eliminates such problems in a straightforward manner. It does so by retaining the octangular propagation mechanism of earlier algorithms while keeping track of the particular locations at which propagated waves of accumulating travel cost either refract or diffract. The approach also holds promise for significant improvement in areas ranging from dispersion modeling and shape analysis to interpolation and the delineation of cost-minimizing paths. 相似文献
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Phil Bartie William Mackaness 《International journal of geographical information science》2017,31(4):805-824
Visibility modelling calculates what an observer could theoretically see in the surrounding region based on a digital model of the landscape. In some cases, it is not necessary, nor desirable, to compute the visibility of an entire region (i.e. a viewshed), but instead it is sufficient and more efficient to calculate the visibility from point to point, or from a point to a small set of points, such as computing the intervisibility of predators and prey in an agent-based simulation. This paper explores how different line-of-sight (LoS) sample ordering strategies increase the number of early target rejections, where the target is considered to be obscured from view, thereby improving the computational efficiency of the LoS algorithm. This is of particular importance in dynamic environments where the locations of the observers, targets and other surface objects are being frequently updated. Trials were conducted in three UK cities, demonstrating a robust fivefold increase in performance for two strategies (hop, divide and conquer). The paper concludes that sample ordering methods do impact overall efficiency, and that approaches which disperse samples along the LoS perform better in urban regions than incremental scan methods. The divide and conquer method minimises elevation interception queries, making it suitable when elevation models are held on disk rather than in memory, while the hopping strategy was equally fast, algorithmically simpler, with minimal overhead for visible target cases. 相似文献
16.
HARVEY J. MILLER 《International journal of geographical information science》2013,27(3):287-301
Abstract The space-time Of time geographical framework is a powerful perspective from which to analyse human behaviour. One of the central concepts in this framework is the space-time prism, which models individual accessibility to an environment. In this paper, the derivation and manipulation of space-time prism concepts within a geographical information system (GIS) are discussed. The required system inputs and desired outputs are identified and a generic GIS based procedure is presented Given these basic requirements, issues are discussed which can determine the feasibility of current GIS technology to handle the derivation of space-time prism concepts. 相似文献
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竞争型公共设施区位决策——概念、选址原则及模型构建 总被引：4，自引：3，他引：1
竞争型公共设施竞争性、公益性并存,其区位决策相对更加复杂。首先提出了“竞争型公共设施”的概念,指出“兼顾效率与公平的空间均衡”是其选址的基本原则,并概括出具体选址要求：遵循供需双方的空间相互作用模式、限制至邻近设施的最大出行成本、追求总出行成本最小化、约束设施规模门槛、与低层级设施在出行成本上相区分等。其次构建了基于概率分配规则的重力P中值模型,通过纳入设施规模因子实现区位和规模同步求解,并对邻近设施最大出行成本和设施最小规模进行约束,以实现空间公平-效率、服务质量公平与规模效率等多重目标。最后经过实证检验,优化后的设施布局更为均衡合理。 相似文献
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Georgios Technitis Walied Othman Kamran Safi Robert Weibel 《International journal of geographical information science》2013,27(6):912-934
For applications in animal movement, we propose a random trajectory generator (RTG) algorithm that combines the concepts of random walks, space-time prisms, and the Brownian bridge movement model and is capable of efficiently generating random trajectories between a given origin and a destination point, with the least directional bias possible. Since we provide both a planar and a spherical version of the algorithm, it is suitable for simulating trajectories ranging from the local scale up to the (inter-)continental scale, as exemplified by the movement of migrating birds. The algorithm accounts for physical limitations, including maximum speed and maximum movement time, and provides the user with either single or multiple trajectories as a result. Single trajectories generated by the RTG algorithm can be used as a null model to test hypotheses about movement stimuli, while the multiple trajectories can be used to create a probability density surface akin to Brownian bridges. 相似文献
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西方城市女性时空行为研究的新趋势及其对中国的启示 总被引：1，自引：1，他引：0
为满足当前城市社会发展与城市建设需要,西方女性时空行为研究近年来取得了长足进展,研究主题覆盖行为特征、社会公平、可持续性等方面。中国城市女性在转型期同样面临着重大的挑战,城市空间的性别不平等正在深刻地影响女性的日常行为与生活质量。本文系统梳理了近50年来西方女性时空行为研究成果,介绍了女性通勤行为、非工作活动等传统议题和家庭关系、联合行为、可达性等新问题的研究进展,并总结了女性时空行为研究的理论解释。西方女性时空行为研究早期关注经济转型背景下的女性出行行为,对就业可达性、通勤和非工作活动的性别差异进行了大量研究。近年来,西方研究呈现出多元化趋势,研究重点转向家庭关系、家庭联合行为与时空可达性等新主题,指出女性在日常生活中面临社会排斥与空间不平等。为理解女性时空行为模式的形成机制,学者从经济学、社会学、地理学等角度进行探讨,提出了地租与工资理论、劳动力市场隔离理论、家庭责任假说、女性的自我认知与社会文化、家庭资源分配说、时空固定性制约等解释理论。这些研究为中国城市女性时空行为研究提供了借鉴。针对中国女性面临的城市社会转型的独特背景,其时空行为受制度、家庭和自身的多重制约,提出了中国城市女性时空行为研究的框架和未来研究方向。 相似文献