基于栅格数据和图论算法的生态廊道识别

利用图论中最短路算法思想和ArcGIS的空间分析功能,对生境中动物迁徙廊道的识别与构建进行研究。通过对具有不同空间自相关特征的模拟景观进行分析,发现该方法具有较好的适应性,能识别出不同类型模拟景观的廊道。在模拟景观分析的基础上,将该算法应用于长沙市大河西先导区,计算了先导区重要栖息地之间的廊道。研究表明该计算方法提取的生态廊道具有明显的冗余性,充分反映了物种在不同栖息地之间迁徙的需求,具有一定的生态学意义。同时廊道提取结果在一定程度上反映了城市发展对生态系统尤其是生态廊道的胁迫与挤占。通过对廊道空间结构的分析还发现生态廊道存在一定的瓶颈区域,对该区域的生态恢复与重建将对物种多样性的保持起到关键作用。该方法为区域土地管理以及生态环境保护规划提供一定的科学依据。     

A method for finding a least-cost wide path in raster space

Given a grid of cells each having an associated cost value, a raster version of the least-cost path problem seeks a sequence of cells connecting two specified cells such that its total accumulated cost is minimized. Identifying least-cost paths is one of the most basic functions of raster-based geographic information systems. Existing algorithms are useful if the path width is assumed to be zero or negligible compared to the cell size. This assumption, however, may not be valid in many real-world applications ranging from wildlife corridor planning to highway alignment. This paper presents a method to solve a raster-based least-cost path problem whose solution is a path having a specified width in terms of Euclidean distance (rather than by number of cells). Assuming that all cell values are positive, it does so by transforming the given grid into a graph such that each node represents a neighborhood of a certain form determined by the specified path width, and each arc represents a possible transition from one neighborhood to another. An existing shortest path algorithm is then applied to the graph. This method is highly efficient, as the number of nodes in the transformed graph is not more than the number of cells in the given grid and decreases with the specified path width. However, a shortcoming of this method is the possibility of generating a self-intersecting path which occurs only when the given grid has an extremely skewed distribution of cost values.     

A new algorithm to find raster-based least-cost paths using cut and fill operations

We developed a least-cost path analysis algorithm that satisfies a slope threshold condition in hilly terrain. The new algorithm uses an expanding moving-window to explore a combination of cells that satisfy an elevation threshold condition and then supplements this by executing cut and fill operations when there are obstacle cells between source and destination cells. Cut and fill factors regarding the difference in the actual elevation and revised elevation are considered and a least-cost path is analyzed after calculating the accumulated travel cost to the destination point. After applying the developed algorithm to synthetic and real-world data, the least accumulated travel cost from the source point can then be calculated for all cells on the raster surface by considering various slope thresholds, moving-window sizes and raster data resolutions. This algorithm can be implemented as a useful tool in GIS software as well as engineering design software utilized in the construction and mining industries.     

A spatial and statistical analysis of the impact of transformation of raster cost surfaces on the variation of least-cost paths

Planners who are involved in locational decision-making often use raster-based geographic information systems to quantify the value of land in terms of suitability or cost for a certain use. From a computational point of view, this process can be seen as a transformation of one or more sets of values associated with a grid of cells into another set of such values through a function reflecting one or more criteria. While it is generally anticipated that different transformations lead to different ‘best’ locations, little has been known on how such differences arise (or do not arise). The paper attempts to answer this question in the context of path planning through a series of computational experiments using a number of random landscape grids with a variety of spatial and nonspatial structures. In the experiments, we generated least-cost paths on a number of cost grids transformed from the landscape grids using a variety of transformation parameters and analyzed the locations and (weighted) lengths of those paths. Results show that the same pair of terminal cells may well be connected by different least-cost paths on different cost grids though derived from the same landscape grid and that the variation among those paths is affected by how given values are distributed in the landscape grid as well as by how derived values are distributed in the cost grids. Most significantly, the variation tends to be smaller when the landscape grid contains more distinct patches of cells potentially attracting or distracting cost-saving passage or when the cost grid contains a smaller number of low-cost cells.     

On applying viewshed analysis for determining least-cost paths on Digital Elevation Models

The concept of computing least-cost paths has been proposed and discussed for a few decades but only in simplified form due to the limited computational resources in the past. With the advancement of computer technology in speed and data storage, it is now possible to implement least-cost path algorithms with realistic conditions. In this paper, we present our implementations of least-cost paths by integrating viewshed information computed from digital elevation models. Our implementations and analyses include four possible types of paths. They are scenic paths, strategic paths, hidden paths, and withdrawn paths. While possible applications of these least-cost paths include planning of civil engineering, military and environmental planning, other extensions can be formulated without much difficulty.     

Refining Hernando de Soto's Route Using Electric Circuit Theory and CircuitScape

A least-cost path (LCP) analysis and a circuit theory analysis were used to estimate the path followed by Hernando de Soto as he crossed the Appalachian Mountains between Tennessee and North Carolina in 1540. The analyses were performed on the slope of the terrain and on a function of the slope that estimates hiking speed. The analyses were performed on data sets with 90-m and 180-m spatial resolutions. Three potential routes were found and compared. The most novel element of the work was the use of CircuitScape software, which returned the likelihood that each cell in the raster data was a part of de Soto's route. This clearly illuminated areas where the estimated routes were more constrained and areas where de Soto would have been free to take alternate paths without increasing travel time. The two analysis methods, LCP and circuit theory, corroborate one another and provide insight into de Soto's journey.     

Ant intelligence for solving optimal path‐covering problems with multi‐objectives

Conventional methods have difficulties in forming optimal paths when raster data are used and multi‐objectives are involved. This paper presents a new method of using ant colony optimization (ACO) for solving optimal path‐covering problems on unstructured raster surfaces. The novelty of this proposed ACO includes the incorporation of a couple of distinct features which are not present in classical ACO. A new component, the direction function, is used to represent the ‘visibility’ in the path exploration. This function is to guide an ant walking toward the final destination more efficiently. Moreover, a utility function is proposed to reflect the multi‐objectives in planning applications. Experiments have shown that classical ACO cannot be used to solve this type of path optimization problems. The proposed ACO model can generate near optimal solutions by using hypothetical data in which the optimal solutions are known. This model can also find the near optimal solutions for the real data set with a good convergence rate. It can yield much higher utility values compared with other common conventional models.     

Multistate supernetwork approach to modelling multi-activity,multimodal trip chains

Least-costs path finding methods belong to the standard toolkit of geographical information science and allow one to assign trips with known origin and destination to a transport network. An extension of the network representation is proposed that allows one to model complete trip chains (tours) that may involve multiple transport modes and multiple activities, as a least-cost path through the network. The extension is based on the notion that link costs may change as a consequence of activity and vehicle choices during the tour. The extended network or supernetwork contains as many copies of the network as there are possible activity–vehicle states and additional state transition links to interconnect them. In this way, not only the generalized link cost function, but also the start and end points of a path can be defined state dependently. A least-cost path through a multistate network defines an optimal sequence of travelling, transferring, parking, conducting activities and dropping off products of activities. An application shows how a multistate network can be constructed and used to assess the impacts of network design variables on path choice.     

Modelling surface drainage patterns in altered landscapes using LiDAR

The detailed topographic information contained in light detection and ranging (LiDAR) digital elevation models (DEMs) can present significant challenges for modelling surface drainage patterns. These data frequently represent anthropogenic infrastructure, such as road embankments and drainage ditches. While LiDAR DEMs can improve estimates of catchment boundaries and surface flow paths, modelling efforts are often confounded difficulties associated with incomplete representation of infrastructure. The inability of DEMs to represent embankment underpasses (e.g. bridges, culverts) and the problems with existing automated techniques for dealing with these problems can lead to unsatisfactory results. This is often dealt with by manually modifying LiDAR DEMs to incorporate the effects of embankment underpasses. This paper presents a new DEM pre-processing algorithm for removing the artefact dams created by infrastructure in sites of embankment underpasses as well as enforcing flow along drainage ditches. The application of the new algorithm to a large LiDAR DEM of a site in Southwestern Ontario, Canada, demonstrated that the least-cost breaching method used by the algorithm could reliably enforce drainage pathways while minimizing the impact to the original DEM.     

基于耗费场的最优路径算法研究

在GIS中,有一类应用是基于连续分布耗费场的最优路径计算问题,如公路选线等。该文首先采用规则格网对耗费场进行建模,进而基于规则格网表现,分别建立网络实现模型和元胞自动机实现模型,并探讨了基于元胞自动机模型的最优路径算法,通过实例研究,说明了算法的正确性。     

An efficient method for single-facility location and path-connecting problems in a cell map

This article presents an efficient method for simultaneously finding both the Weber cell and optimal connective paths in a grid. As numerous barriers of arbitrary shape and weighted regions are distributed in the cell map of this research, the problem scenario is similar to working out a real-life facility location selection and path-routing problems in a geographical map. In this study, the Weber problem of finding a single-facility location from an accumulation cost table is generated by a grid wave propagation method (higher-geometry maze router). After finding the Weber point (cell), optimal connective paths with minimum total weighted cost are backtracked between the Weber location cell and the demand cells. This new computation algorithm with linear time and space complexity can be integrated as a spatial analytical function within GIS.     

技术关联与土地财政对区域产业演化的影响

区域产业演化是新产业进入、旧产业退出的过程,新产业为区域创造新发展路径。受本地技术关联驱动,区域产业演化表现出路径依赖,而外生的制度因素可以改变新路径的方向。基于中国城市土地出让收入数据及工业企业数据库,分析历年土地财政和产业演化的时空分异特征,并利用Logit条件回归模型在城市-产业尺度实证检验技术关联与土地财政对区域产业演化的影响。研究发现：①技术关联促进了中国区域产业新路径产生。②土地财政总体上阻碍了中国区域产业新路径的产生。③城市的土地财政依赖总体上加剧了产业演化的路径依赖,阻碍了我国产业突破既有发展路径和实现转型升级。④土地财政对产业演化的影响存在区域差异：在东部地区,土地供给增长显著促进区域产业发展;土地财政促进了区域内生产业发展,强化了技术关联对产业发展新路径的积极效应。在中部,土地财政的扩张效应促进了区域发展及其路径突破,区域产业演化受产业转移影响,不受本地技术关联驱动。在西部,土地财政抑制了区域发展,本地技术关联的影响不显著。在东北,土地财政带来的土地供给增长有助于区域产业发展,产业演化存在路径依赖。     

Complexity in a cellular model of river avulsion

We propose a new model of river avulsion that emphasizes simplicity, self-organization, and unprogrammed behavior rather than detailed simulation. The model runs on a fixed cellular grid and tracks two elevations in each cell, a high elevation representing the channel (levee) top and a low one representing the channel bottom. The channel aggrades in place until a superelevation threshold for avulsion is met. After an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation. Flow path depends sensitively on floodplain topography, particularly the presence of former abandoned channels. Several behavioral characteristics emerge consistently from this simple model: (1) a tendency of the active flow to switch among a small number of channel paths, which we term the active channel set, over extended periods, leading to clustering and formation of multistory sand bodies in the resulting deposits; (2) a tendency for avulsed channels to return to their previous paths, so that new channel length tends to be generated in relatively short segments; and (3) avulsion-related sediment storage and release, leading to pulsed sediment output even for constant input. Each of these behaviors is consistent with observations from depositional river systems. A single-valued threshold produces a wide variety of avulsion sizes and styles. Larger “nodal” avulsions are rarer because pre-existing floodplain topography acts to steer flow back to the active channel. Channel stacking pattern is very sensitive to floodplain deposition. This work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution.     

An application-driven approach to terrain model construction

Terrain is a surface phenomenon that is measured, modelled, and mapped. However, it is continuously variable and must be simulated by points or mathematical equations that are inherently approximations. The error induced by digitally represented terrain can propagate to surface derivatives and geographical information science (GIS) applications where topography is considered. This can lead to uncertainty in model predictions and the use of data that are unfit for the application to which they are intended. This article outlines the problem of uncertainty in terrain representation and demonstrates the consequences for volcanic mudflow modelling. The response of a simple least-cost single flow algorithm to input parameters was investigated in order to assess output variation from the different sources of input variation. Elevation error was modelled with a probability density function (PDF) and propagated through stochastic simulation (Monte Carlo). Such combined uncertainty and sensitivity analyses enabled a qualitative judgement of the relative significance of elevation error on the flow model prediction. Different methods for terrain model construction were considered and show that supplementing global positioning system (GPS) measurements with information from field notes and reconnaissance photographs greatly improved the model performance and reduced the uncertainty. It is concluded that in terms of validity of model results, there is no substitute for constructing an elevation model that is informed by the terrain.     

栅格空间中三维地学实体拓扑关系表达的K6N9-I模型

论述栅格空间中三维地学实体拓扑空间关系研究的理论基础和现实意义,基于数字拓扑理论定义了栅格实体的6邻域内部I6、6邻域边界B6和k阶6邻域E6k,并以此分别替换9-I模型中实体的内部I、边界B和外部E,形成一种适用于栅格空间三维实体拓扑关系描述和分析的新9-I模型,即k阶6邻9-I模型(K6N9-I)。以基于规则六面体表达的地学实体为研究对象,通过扩展关系数据库SQL形成空间关系查询语言,实现了栅格空间中三维地学实体拓扑关系的定性表示和定量计算。以若干地学实体为例进行了初步实验,表明该模型实用方便,且在复杂地学实体的度量、方位等空间关系研究方面亦有较好的应用前景。     

GIS‐Based Indices for Comparing Airline Flight‐Path Vulnerability to Volcanoes

Volcanic ash can cause physical damage to an aircraft to the point of mechanical and electrical malfunction. In the event of an ash plume, aircraft would likely be diverted or grounded, leading to economic losses. This article presents two indices to compare the economic vulnerability of flight paths to volcanic ash plumes. The first index includes three factors for a flight path: wind direction, distance to the volcano, and flight‐path attributes (i.e., number of flights per day, number of potential passengers, and average ticket cost). The second index compares the threat posed by different volcanoes to an airline flight‐path network. A case study is presented for two airlines in the northwest United States to a Mt. Adams eruption. The results show that although the first airline has more flight paths in the region, the second airline is slightly more vulnerable due to the spatial relationships of its flight paths to the volcano and their attributes.     

Modelling the network component of geographical information systems

Abstract

This paper presents a data model to manage networks with a Geographical Information System with some consideration of the path operator. The data model is based on the merge of graph theory concepts and the object-oriented paradigm. The introduction of the Master_nodes (with respect to Master_edges) allows definition of a node (with respect to an edge) as an abstraction of a sub-network. A network can be defined using several levels of definition (detail) following the importance of the nodes (with respect to the edges) within an application. The object-oriented concepts are applied to both the alphanumerical data part and to the modelling part of the topology of the graph. The data manipulation operators are basic operators. These operators are the union, an intersection and a difference. More elaborated operators, such as under constraints paths, are obtained by combining these basic operators. We present some considerations of the path operator in a GIS context and introduce the concept of the ‘Open Graph Assumption’ and the notion of direction. These notions take full advantage of the data model and represent an alternative way of defining the path operator. This modelling is well adapted to take account of multi-level networks (i.e., the definition of a view in the context of a multi-user configuration or cartographic generalization).     

基于遥感的黄河三角洲蒸散的动态分析

Evapotranspiration (ET) is an important parameter for water resource management. Compared to the traditional ET computation and measurement methods, the ET computation method based on remote sensing has the advantages of quickness, precision, raster mapping and regional scale. SEBAL, an ET computation model using remote sensing method is based on the surface energy balance equation which is a function of net radiance flux, soil heat flux, sensible heat flux and latent heat flux. The former three fluxes can be computed through the parameters retrieved from remote sensing image, then the latent heat flux can be obtained to provide energy for ET. Finally we can obtain the daily ET. In this study SEBAL was applied to compute ET in the Yellow River Delta of China where water resource faces a rigorous situation. Three Landsat TM images and meteorology data of 1999 were used for ET computation, and spatial and temporal change patterns of ET in the Yellow River Delta were analysed.     

Dynamic analysis of evapotranspiration based on remote sensing in Yellow River Delta

Evapotranspiration (ET) is an important parameter for water resource management. Compared to the traditional ET computation and measurement methods, the ET computation method based on remote sensing has the advantages of quickness, precision, raster mapping and regional scale. SEBAL, an ET computation model using remote sensing method is based on the surface energy balance equation which is a function of net radiance flux, soil heat flux, sensible heat flux and latent heat flux. The former three fluxes can be computed through the parameters retrieved from remote sensing image, then the latent heat flux can be obtained to provide energy for ET. Finally we can obtain the daily ET. In this study SEBAL was applied to compute ET in the Yellow River Delta of China where water resource faces a rigorous situation. Three Landsat TM images and meteorology data of 1999 were used for ET computation, and spatial and temporal change patterns of ET in the Yellow River Delta were analysed.     

A Review of: Environmental Modelling with GIS.

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.