共查询到20条相似文献，搜索用时 15 毫秒
1.
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
2.
Seamus Coveney 《International journal of geographical information science》2013,27(3):467-483
Airborne LiDAR (light detection and ranging) data are now commonly regarded as the most accurate source of elevation data for medium-scale topographical modelling applications. However, quoted LiDAR elevation error may not necessarily represent the actual errors occurring across all surfaces, potentially impacting the reliability of derived predictions in Geographical Information Systems (GIS). The extent to which LiDAR elevation error varies in association with land cover, vegetation class and LiDAR data source is quantified relative to dual-frequency global positioning system survey data captured in a 400-ha area in Ireland, where four separate classes of LiDAR point data overlap. Quoted elevation errors are found to correspond closely with the minimum requirement recommended by the American Society of Photogrammetry and Remote Sensing for the definition of 95% error in urban areas only. Global elevation errors are found to be up to 5 times the quoted error, and errors within vegetation areas are found to be even larger, with errors in individual vegetation classes reaching up to 15 times the quoted error. Furthermore, a strong skew is noted in vegetated areas within all the LiDAR data sets tested, pushing errors in some cases to more than 25 times the quoted error. The skew observed suggests that an assumption of a normal error distribution is inappropriate in vegetated areas. The physical parameters that were found to affect elevation error most fundamentally were canopy depth, canopy density and granularity. Other factors observed to affect the degree to which actual errors deviate from quoted error included the primary use for which the data were acquired and the processing applied by data suppliers to meet these requirements. 相似文献
3.
戈壁风蚀面与植被覆盖面地表性质粗糙度长度的确定 总被引：9，自引：5，他引：4
以Monin-Obukhov相似性理论为基础, 利用量纲分析法分别推导出不同层结稳定度下确定戈壁风蚀面与植被覆盖面空气动力学参数的物理模型, 并利用该模型研究了粗糙度长度与粗糙元性质, 流经近地层流体特征以及大气层结稳定度之间的关系。得出以下结论: 戈壁风蚀面上空气动力学粗糙度长度与砾石粒径、高度、覆盖度、自由风速、摩擦速度以及大气层结稳定度有关; 植被覆盖面空气动力学粗糙度长度取决于植被类型、植被高度、覆盖度、零平面位移高度、自由风速、摩擦速度以及大气层结稳定度。 相似文献
4.
Amii R. Darnell Andrew A. Lovett Jenni Barclay Richard A. Herd 《International journal of geographical information science》2013,27(8):1171-1191
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. 相似文献
5.
Min Liu András Bárdossy Jing Li Yuan Jiang 《International journal of geographical information science》2013,27(7):1281-1308
Solar radiation not only sustains the lives on the Earth, but also creates spatial and temporal variations of hydrological ingredients, such as vegetation, soil moisture, and snow. Precise quantification of spatial solar radiation incident on the Earth's surface which accounts for the topographic modulation, especially in complex terrain, underpins the study of many catchment hydro-meteorological and hydro-ecological processes. Topography is a key parameter that affects the spatial solar radiation pattern across different scales. This article addresses the issue of modelling spatial variability of actual solar radiation caused by topography from the hydrological perspective. Models with different algorithms and different complexities, from the simple empirical equations to process-based physical approach, have been developed to parameterize and calculate the potential radiation (under clear-sky condition) and the actual radiation (under overcast cloudy condition). Based on a review of the general steps of solar radiation modelling and the corresponding models for each step, two models with easily or globally available data for spatial solar radiation modelling in complex terrain, namely, the physically parameterized, remote-sensing-oriented Heliosat-2 model and the sunshine duration-based Angström–Prescott regression model are selected and implemented in a GIS framework. The capability of both models for simulation of cloudy-sky radiation on horizontal surfaces has been verified against observed station data showing an R 2 greater than 0.9. The validity of the models for modelling inclined surface is tested by comparing against each other, which has shown a satisfactory agreement and demonstrated that the simple Angström–Prescott method performed reasonably well compared with the more elaborate Heliosat-2 method. Scale sensitivity of the models and the shading effect are examined with different digital elevation model (DEM) resolutions from 30 to 500 m and reveal the existence of a threshold grid size to resolve the topography-induced spatial solar radiation variability. Spatial mapping of potential solar radiation and actual solar radiation has been demonstrated in a small catchment in Southern Germany, with a spatial difference up to 30% in winter and 5% in summer. This may lead to a significant difference for the energy-limited hydrological processes, such as snowmelt, and evapotranspiration. 相似文献
6.
Yue Lin Yuyang Cai Yue Gong Lin Li 《International journal of geographical information science》2013,27(12):2406-2423
ABSTRACTUrban landmarks are of significant importance to spatial cognition and route navigation. However, the current landmark extraction methods mainly focus on the visual salience of landmarks and are insufficient for obtaining high extraction accuracy when the size of the geographical dataset varies. This study introduces a random forests (RF) classifier combining with the synthetic minority oversampling technique (SMOTE) in urban landmark extraction. Both GIS and social sensing data are employed to quantify the structural and cognitive salience of the examined urban features, which are available from basic spatial databases or mainstream web service application programming interfaces (APIs). The results show that the SMOTE-RF model performs well in urban landmark extraction, with the values of recall, precision, F-measure and AUC reaching 0.851, 0.831, 0.841 and 0.841, respectively. Additionally, this method is suitable for both large and small geographical datasets. The ranking of variable importance given by this model further indicates that certain cognitive measures – such as feature class, Weibo popularity and Bing popularity – can serve as crucial factors for determining a landmark. The optimal variable combination for landmark extraction is also acquired, which might provide support for eliminating the variable selection requirement in other landmark extraction methods. 相似文献
7.
GIS and ANN model for landslide susceptibility mapping 总被引：1，自引：0，他引：1
XU Zeng-wang 《地理学报》2001,11(3):374-381
Landslide hazard is as the probability of occurrence of a potentially damaging landslide phenomenon within specified period of time and within a given area. The susceptibility map provides the relative spatial probability of landslides occurrence. A study is presented of the application of GIS and artificial neural network model to landslide susceptibility mapping, with particular reference to landslides on natural terrain in this paper. The method has been applied to Lantau Island, the largest outlying island within the territory of Hong Kong. A three-level neural network model was constructed and trained by the back-propagate algorithm in the geographical database of the study area. The data in the database includes digital elevation modal and its derivatives, landslides distribution and their attributes, superficial geological maps, vegetation cover, the raingauges distribution and their 14 years 5-minute observation. Based on field inspection and analysis of correlation between terrain variables and landslides frequency, lithology, vegetation cover, slope gradient, slope aspect, slope curvature, elevation, the characteristic value, the rainstorms corresponding to the landslide, and distance to drainage line are considered to be related to landslide susceptibility in this study. The artificial neural network is then coupled with the ArcView3.2 GIS software to produce the landslide susceptibility map, which classifies the susceptibility into three levels: low, moderate, and high. The results from this study indicate that GIS coupled with artificial neural network model is a flexible and powerful approach to identify the spatial probability of hazards. 相似文献
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9.
GIS and ANN model for landslide susceptibility mapping 总被引：4，自引：0，他引：4
XU Zeng-wang 《地理学报(英文版)》2001,11(3):374-381
1 IntroductionThe population growth and the expansion of settlements and life-lines over hazardous areas exert increasingly great impact of natural disasters both in the developed and developing countries. In many countries, the economic losses and casualties due to landslides are greater than commonly recognized and generate a yearly loss of property larger than that from any other natural disasters, including earthquakes, floods and windstorms. Landslides in mountainous terrain often occur a… 相似文献
10.
中国适垦耕地空间分异特征研究 总被引：3，自引：0，他引：3
基于GIS空间分析技术,利用数字地形高程图生成地形高程和坡度分级图,将地形高程分级图、地形坡度分级图、2000年耕地分布图和分县行政区划图叠加,提取2000年分县耕地地形分异数据,计算2006年分县适垦耕地面积,以适垦耕地指数和人均适垦耕地面积为指标,分析我国适垦耕地的空间分异特征。结果表明:1)我国耕地的地形分异特点是随着地形高程和坡度的增加,耕地面积均呈现快速下降的趋势,耕地主要集中于海拔500 m以下且坡度较小的地域。2)适垦耕地的空间分异主要受地形条件控制,海拔较低、地形平缓的平原、盆地和河谷适垦耕地指数一般在50%以上,而海拔较高、地形起伏较大的高原、山地和丘陵地区指数值普遍低于30%。3)我国人均适垦耕地面积空间分布的总体特征是北多南少,人均适垦耕地面积在0.2 hm2以上的高类和较高类大都分布在北方地区,而人均适垦耕地面积在0.067 hm2以下的低类和较低类主要集中于青藏高原及东南沿海地区。 相似文献
11.
Federico Ferretti 《The Journal of geography》2017,116(1):3-19
This article addresses Patrick Geddes's relationship with geography and visual education by focusing on his collaboration with the network of the anarchist geographers Élie, Élisée, and Paul Reclus. Drawing on empirical archival research, it contributes to the current debates on geographies of anarchist education and on geographic teaching. The main argument is that the collaboration between Geddes and the Recluses inaugurated specific strategies of multisensorial geographic education that were not limited to the sight, and that questioned and relativized the uniqueness of the observer's standpoint through devices like the Hollow Globe. Focusing on apparatuses like the Outlook Tower's geographic exposition and the Valley Section, it shows in which ways Geddes engaged with Élisée Reclus's critique of representation and geography as a visual discipline. 相似文献
12.
城市暴雨内涝情景模拟与灾害风险评估 总被引：5，自引：1，他引：4
Scenario modelling and the risk assessment of natural disasters is one of the hot-spots in disaster research.However,up until now,urban natural disaster risk assessments lack common procedures and programmes.This paper selects rainstorm waterlogging as a disaster to research,which is one of the most frequently occurring hazards for most cities in China.As an example,we used a small-scale integrated methodology to assess risks relating to rainstorm waterlogging hazards in the Jing’an District of Shanghai.Based on the basic concept of disaster risk,this paper applies scenario modelling to express the risk of small-scale urban rainstorm waterlogging disasters in different return periods.Through this analysis of vulnerability and exposure,we simulate different disaster scenarios and propose a comprehensive analysis method and procedure for small-scale urban storm waterlogging disaster risk assessments.A grid-based Geographical Information System (GIS) approach,including an urban terrain model,an urban rainfall model and an urban drainage model,was applied to simulate inundation area and depth.Stage-damage curves for residential buildings and contents were then generated by the loss data of waterlogging from field surveys,which were further applied to analyse vulnerability,exposure and loss assessment.Finally,the ex-ceedance probability curve for disaster damage was constructed using the damage of each simulated event and the respective exceedance probabilities.A framework was also devel-oped for coupling the waterlogging risk with the risk planning and management through the exceedance probability curve and annual average waterlogging loss.This is a new explora-tion for small-scale urban natural disaster scenario simulation and risk assessment. 相似文献
13.
中国比辐射率空间分布特征分析 总被引：1，自引：0，他引：1
使用2003-2013年MOD/MYD11C3地表比辐射率光谱数据、MOD/MYD13C2植被指数光谱数据,合成全国各月地表比辐射率、NDVI(Normalized Difference Vegetation Index)。基于DEM数据分析比辐射率与NDVI随海拔、坡向的变化规律。结果表明:(1)比辐射率低值段(0.960~0.970)主要分布在我国西北荒漠地区,面积比例全年变化不显著,代表了干燥裸土下低比辐射率的特征;中值段(0.970~0.975)分布于我国大部分植被覆盖地区,面积比例夏高冬低,代表植被覆盖下混合像元的中比辐射率特征;高值段(0.975~0.980)位于我国部分高海拔和高纬度地区,面积比例冬高夏低,代表冰雪与植被混合像元的高比辐射率特征。(2)比辐射率与NDVI随坡向变化呈明显的"双峰双谷"分布。东南坡、西坡为峰值,最大值位于东南坡;南坡、北坡为谷值,最小值位于北坡。两者变化一致性很高。受不同坡向太阳方位角下的地形敏感性与植被覆盖综合影响,比辐射率表现出随坡向的峰谷变化规律。(3)随海拔升高,比辐射率呈垂直地带性变化。存在3个下降区:250 m~1250 m、2500 m~3000 m和4750 m~6000 m;3个上升区:1250 m~2500 m、3000 m~4750 m和6000 m~6500 m。这与NDVI随海拔变化特征类似,反映垂直下垫面植被变化对比辐射率空间分布的影响。 相似文献
14.
Historical geographic information systems (GIS) scholarship has provided important insights into a broad spectrum of historical questions in recent years. This article contributes to the emerging field of historical GIS by employing map algebra and transect analysis to quantitatively assess topographical change resulting from rapid urban growth in New York City since the first quarter of the nineteenth century. These methodological techniques enable a systematic comparison of Manhattan's historical and contemporary topography through a spatial analysis of various topographic metrics, including the extent of positive and negative elevation change, shifts in elevation range, the percentage of geographic area that experienced elevation changes, and the estimated volume of Earth added to and removed from particular areas within the study site. The results indicate that there were more valleys filled than hills leveled on Manhattan's East Side, whereas the reverse was the case on the West Side. The West Side, however, experienced considerably more topographic changes than its eastern counterpart, in large part due to the former's more rugged terrain. Overall, the evidence suggests that although Manhattan's topography has been radically transformed in certain respects, the broader spatial pattern of topographic variation has remained largely constant. These findings, therefore, can be used to support competing narrative claims concerning the significance of the topographical transformations that resulted from the urbanization process in New York City. 相似文献
15.
《地理学报(英文版)》2017,(11)
Geomorphometry,the science of digital terrain analysis(DTA),is an important focus of research in both geomorphology and geographical information science(GIS).Given that 70% of China is mountainous,geomorphological research is popular among Chinese scholars,and the development of GIS over the last 30 years has led to significant advances in geomorphometric research.In this paper,we review Chinese progress in geomorphometry based on the published literature.There are three major areas of progress:digital terrain modelling methods,DTA methods,and applications of digital terrain models(DTMs).First,traditional vector-and raster-based terrain modelling methods,including the assessment of uncertainty,have received widespread attention.New terrain modelling methods such as unified raster and vector,high-fidelity,and real-time dynamic geographical scene modelling have also attracted research attention and are now a major focus of digital terrain modelling research.Second,in addition to the popular DTA methods based on topographical derivatives,geomorphological features,and hydrological factors extracted from DTMs,DTA methods have been extended to include analyses of the structure of underlying strata,ocean surface features and even socioeconomic spatial structures.Third,DTMs have been applied to fields including global climate change,analysis of various typical regions,lunar surface and other related fields.Clearly,Chinese scholars have made significant progress in geomorphometry.Chinese scholars have had the greatest international impact in areas including high-fidelity digital terrain modelling and DTM-based regional geomorphological analysis,particularly in the Loess Plateau and the Tibetan Plateau regions. 相似文献
16.
Guonian LV Liyang XIONG Min CHEN Guoan TANG Yehua SHENG Xuejun LIU Zhiyao SONG Yuqi LU Zhaoyuan YU Ka ZHANG Meizhen WANG 《地理学报(英文版)》2017,27(11):1389-1412
Geomorphometry, the science of digital terrain analysis (DTA), is an important focus of research in both geomorphology and geographical information science (GIS). Given that 70% of China is mountainous, geomorphological research is popular among Chinese scholars, and the development of GIS over the last 30 years has led to significant advances in geomorphometric research. In this paper, we review Chinese progress in geomorphometry based on the published literature. There are three major areas of progress: digital terrain modelling methods, DTA methods, and applications of digital terrain models (DTMs). First, traditional vector- and raster-based terrain modelling methods, including the assessment of uncertainty, have received widespread attention. New terrain modelling methods such as unified raster and vector, high-fidelity, and real-time dynamic geographical scene modelling have also attracted research attention and are now a major focus of digital terrain modelling research. Second, in addition to the popular DTA methods based on topographical derivatives, geomorphological features, and hydrological factors extracted from DTMs, DTA methods have been extended to include analyses of the structure of underlying strata, ocean surface features and even socioeconomic spatial structures. Third, DTMs have been applied to fields including global climate change, analysis of various typical regions, lunar surface and other related fields. Clearly, Chinese scholars have made significant progress in geomorphometry. Chinese scholars have had the greatest international impact in areas including high-fidelity digital terrain modelling and DTM-based regional geomorphological analysis, particularly in the Loess Plateau and the Tibetan Plateau regions. 相似文献
17.
城市不同下垫面的能量平衡及温度差异模拟 总被引：2，自引：0，他引：2
城市能量平衡是研究城市热岛效应的物理基础。利用北京市教学植物园2010年的实测数据,设置不同类型下垫面(植被覆盖类型:林地、草地和不透水层覆盖类型:道路、房屋),利用局地尺度城市气象参数化方案模拟并分析了相同气象条件和净辐射通量输入下,不同类型下垫面的显热、潜热通量及蒸散降温效应的差异。结果显示:(1)不同类型下垫面的各能量支出项有明显差异,植被覆盖区域和不透水层覆盖区域的波文比年均值分别为0.28和4.60,且在植被生长季差异较大;(2)城市扩展过程中道路、房屋替换林地、草地的过程,也是显热增加而潜热减少的过程。植被层向不透水层转换的过程中,显热通量年均增加32.74W/m2,潜热通量减少38.87W/m2,储热通量增加7.95W/m2;(3)理论上,植被蒸散的年降温效应使单位面积植被覆盖区域的气温比不透水层区域可低2.63℃。 相似文献
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19.
Kang-Tsung Chang Zhaoxing Li 《International journal of geographical information science》2013,27(7):693-707
Snow courses that measure snow water equivalent (SWE) are clustered and limited in areal coverage in Idaho. This study used a cell-based geographic information system and multiple regression models to construct SWE surfaces from the snow course data by month (January to May) and by watershed. SWE was the dependent variable and location and topographic variables derived from a digital elevation model were used as the independent variables. Multiple regression performed better than the traditional interpolation methods for SWE estimation. The estimated SWE surface can be displayed at different spatial scales through neighbourhood operations, or used directly as a map layer for hydrologic modelling. 相似文献
20.
等高线蕴含的历史高程信息可有效延长地形研究的时间序列,有利于深入挖掘地形变化长期规律,然而,图幅接边处的高程属性错误降低了等高线的数据质量,制约着等高线高程信息的实际应用。针对这一问题,该文提出一种基于层次格网索引的图幅接边处等高线高程错误识别和自动修正方法:首先,将层次格网索引与方向性二邻域算法相结合,以减少数据重复计算;然后,利用等高线空间位置标签及快速排序算法构建强空间位置关系,解决图幅接边处等高线匹配的准确性问题;最后,以高程冲突位点为驱动因子进行逻辑判断,实现等高线高程错误的识别及自动修正。实验结果表明:该方法运算效率较未进行效率优化时提高了203倍,接边处等高线高程错误识别与修正精度的最大值分别达97.71%和91.40%;相较于现有方法,该方法在精度和效率方面表现更佳,对区域性错误和变形等高线具有更高的适用性。 相似文献