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1.
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.
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3.
The paper discusses an approach known as ‘distance‐decayed visibility’, implemented using GIS, to the composition of 3D scenes for static forest landscape visualization. The distance‐decay concept is employed to model a spatial interaction in terms of visibility between any observation points and vegetations visible from those points. The vegetation visibility is measured in level of detail where high visibility uses high level of detail and vice versa. The interaction is modelled mathematically using an exponential decay function. The point distribution of projected models on a 3D scene is calculated in GIS to assign an appropriate value of ‘visibility decay constant’ to relate the distance from the observation point to the vegetations with the level of detail of the vegetations in the function. The advantages of the technique as measured against the quantitative benchmarks of rendering time and the number of polygons computed are addressed. Although the forest landscape of the study area consists of a large number of vegetation models, the technique helps to model the relation of vegetation visibility and viewing distance so realistically that the technique yields the visual quality of the result 3D scene visually and statistically comparable to the finest resolution scene.  相似文献   

4.
The calculation of visibility patterns associated with past monuments and sites is an important element in modern landscape archaeology. These types of investigations have been limited by the inability of current viewshed routines to incorporate vegetation information. The following paper presents a new viewshed algorithm aimed at calculating the probability of locations being visible in the presence of vegetation. To this day, little work has been done to address this limitation, a notable exception is Dean's Permeability Index Model (1997 Dean, D. J. 1997. Improving the accuracy of forest viewsheds using triangulated networks and the visual permeability method.. Canadian Journal of Forest Research, 27: 969–977. [Crossref] , [Google Scholar]). A review of Dean's model is provided here in the light of the new proposed algorithm. The new algorithm is based on mathematical principles found in Beer–Lambert's Attenuation Law, a physics law governing the attenuation of light through a medium. In addition to common viewshed parameters, the routine requires a 3D model of a tree/plant and a layer indicating the spatial distribution and density of vegetation on the landscape. The possibility of varying both, the spatial and density distribution of tree/plants, and the three‐dimensional model representing vegetation makes the model well suited to investigate the impact that vegetation may have on visibility patterns.  相似文献   

5.
A rapid and flexible parallel approach for viewshed computation on large digital elevation models is presented. Our work is focused on the implementation of a derivate of the R2 viewshed algorithm. Emphasis has been placed on input/output (IO) efficiency that can be achieved by memory segmentation and coalesced memory access. An implementation of the parallel viewshed algorithm on the Compute Unified Device Architecture (CUDA), which exploits the high parallelism of the graphics processing unit, is presented. This version is referred to as r.cuda.visibility. The accuracy of our algorithm is compared to the r.los R3 algorithm (integrated into the open-source Geographic Resources Analysis Support System geographic information system environment) and other IO-efficient algorithms. Our results demonstrate that the proposed implementation of the R2 algorithm is faster and more IO efficient than previously presented IO-efficient algorithms, and that it achieves moderate calculation precision compared to the R3 algorithm. Thus, to the best of our knowledge, the algorithm presented here is the most efficient viewshed approach, in terms of computational speed, for large data sets.  相似文献   

6.
中国南方传统聚落景观区划及其利用价值   总被引：16，自引：1，他引：15  
聚落文化景观是文化景观研究的最有效的切入点。由于中国南方地区较为多样化的地理环境和文化背景,传统聚落景观的多样化特点比北方地区表现得更为鲜明。不同地方环境与文化背景下的南方传统聚落景观,表现出较为明显的地域分异和景观意象差异,从而划分出识别性较强的8个聚落景观区和40个景观亚区。8个聚落景观区为:Ⅰ.江浙水乡聚落景观区;Ⅱ.皖赣徽商聚落景观区;Ⅲ.闽粤赣边客家聚落景观区;Ⅳ.浙南闽台沿海丘陵聚落景观区;Ⅴ.岭南广府聚落景观区;Ⅵ.湘鄂赣平原山地聚落景观区;Ⅶ.云贵高原及桂西北多民族聚落景观区;Ⅷ.四川盆地及周边巴蜀聚落景观区。南方传统聚落景观区的保护与利用价值主要表现在其独特的遗产价值、科学价值、美学价值及旅游价值。  相似文献   

7.
A suitable spatial scale needs to be selected in geographical and landscape ecological research, and this requires great consideration as different scales have profound effect on derived landscape spatial patterns. Numerous studies have investigated the effects of different scales on landscape metrics using simulated patterns, but few have been conducted to compare different data sources with variable scale for regional- and landscape-scale assessments. Possibly this has occurred because researchers have been prone to use the best available source, a well-known standard, and easiest to use. This study was conducted to assess the impact of input data resolution on values of landscape pattern metrics in four landscapes at scales 1:10 000, 1:50 000 and 1:100 000. The aim was to determine the applicability of three data sources for thematic models in landscape pattern analyses in the Eastern Baltic region. We found that the utility of CORINE Land Cover data for comprehensive structural assessment in mosaic-type landscapes was very limited, as the level of cartographic generalization excluded many small and linear landscape structure elements with potentially high importance for landscape functioning, such as habitat continuity. We also found that actual area harvested using clearcuts was considerably higher than shown in CORINE data, due to clearcuts size being much smaller than the minimum mapping unit. In the light of this, we suggest using data with spatial resolution corresponding to a cartographic scale of at least 1:50 000, in cases when spatial patches have size up to 25 ha.  相似文献   

8.
李仁杰  谷枫  郭风华  傅学庆 《地理科学》2015,35(9):1086-1094
在已有景观感知度概念和模型基础上,根据景观规模和特征将交通线某一具体位置的景观感知度划分为单点景观、多点景观和组景观感知度,并提出了基于集合表达的交通线景观感知度模型,以解决在一组特定的线性空间单元或区域上开展景观感知的研究和计算问题。以紫荆关长城文化景观为例,利用DEM进行景观视域分析,并引入资源价值、遗存现状等权重因子,实现了紫荆关附近公路和铁路线的景观感知度定量计算。根据景观感知度的空间格局,准确划分了敌台、烽火台和马面等单点景观、墙体景观及各类组景观和综合景观的最佳感知功能路段和最佳观赏位置。总体来看,紫荆关附近的公路线可感知位置连续性更强,铁路线高感知位置相对离散,公路感知效果整体优于铁路感知。交通线景观感知度模型特别适合用于大型造型地貌、宏伟建筑群等景观感知分析,是对旅游景观规划设计方法的一种扩充,能够将旅游景观规划设计从旅游地内部拓展到旅游地外围,对于提高旅游景观导引设计的精准性、提升旅游文化传播效率和增加传播途径等均有理论参考意义和实践应用价值。  相似文献   

9.
As increasingly large‐scale and higher‐resolution terrain data have become available, for example air‐form and space‐borne sensors, the volume of these datasets reveals scalability problems with existing GIS algorithms. To address this problem, a kind of serial algorithm was developed to generate viewshed on large grid‐based digital elevation models (DEMs). We first divided the whole DEM into rectangular blocks in row and column directions (called block partitioning), then processed these blocks with four axes followed by four sectors sequentially. When processing the particular block, we adopted the ‘reference plane’ algorithm to calculate the visibility of the target point on the block, and adjusted the calculation sequence according to the different spatial relationships between the block and the viewpoint since the viewpoint is not always inside the DEM. By adopting the ‘Reference Plane’ algorithm and using a block partitioning method to segment and load the DEM dynamically, it is possible to generate viewshed efficiently in PC‐based environments. Experiments showed that the divided block should be dynamically loaded whole into computer main memory when partitioning, and the suggested approach retains the accuracy of the reference plane algorithm and has near linear compute complexity.  相似文献   

10.
Modern assessment and monitoring of aquatic ecosystems is increasingly based on biota and the “reference condition” approach, in which the observed values (O) of biological variables are compared to those expected in the absence of human disturbance (E). To use this approach, correct estimation and validation of reference conditions are critical. Because appropriate modern or historical data are never available for this approach, palaeolimnological data offer an alternative. We used a calibration data set from 73 profundal sites in semi-pristine Finnish lakes to construct a regression model for estimating expected values for the chironomid Benthic Quality Index (BQI)—a macroinvertebrate metric widely used in bioassessment—from environmental variables that are insensitive to human disturbance. For comparison, reference values were estimated using the European legislative rationale based on a priori lake typology. Performance of the alternative approaches was assessed by internal ‘leave-one-out’ cross-validation using the calibration set and by external cross-validation using independent palaeolimnological data on BQI values representing the historical pristine status of 24 lake basins. Additionally, for 19 of these sites, which vary in their degree of human impact, the ratio of present BQI to that in pristine condition, which shows the degree of actual change, if any, was calculated from palaeolimnological data and compared with the O/E ratios based on the present chironomid data and estimated E. A linear regression model with mean depth and mean/maximum depth ratio as independent variables estimated the reference values of BQI much closer to the observed ones (r 2 = 0.58, RMSEP = 0.65 and r 2 = 0.71 RMSEP = 0.55; for internal and external cross-validation, respectively) than did the typology approach (r 2 = 0.28, RMSEP = 0.86; r 2 = 0.10, RMSEP = 0.97). The regression approach also yielded O/E ratios more similar to the actual ones (r 2 = 0.79, RMSEP = 0.09) than did the typology approach (r 2 = 0.62, RMSEP = 0.23). Our results strongly support the use of lake morphometric variables and modelling instead of categorical lake typology for the establishment of reference conditions for profundal macroinvertebrate communities and demonstrate the utility of palaeolimnological data in the validation of reference values and assessment methods.  相似文献   

11.
This article analyzes lightning/landscape interactions across the State of Colorado. Ten years (2003–2012) of warm season cloud-to-ground (CG) lightning activity are mapped at 500 × 500 m2 to characterize the distribution of thunderstorm activity. Geospatial analyses quantify lightning activity by elevation, physiographic region, and mountain range, and time-series animations outline the general movement of thunderstorms. From these spatio-temporal perspectives, our objective is to elucidate lightning/landscape interactions as they occur over a topographically and climatologically diverse landscape. The information aids meteorologists by exposing orographic and rainshadow effects, mesoscale meteorological effects, fluxes of moisture sources, thunderstorm initiation zones, and thunderstorm movements. Other benefits extend to wildland fire managers, those who maintain lightning-vulnerable infrastructures, and, from a human risk perspective, an overall awareness to those who work and play outdoors. Major findings include (1) elevation alone does not determine the degree of lightning activity, (2) across the state's mountain ranges, lightning density varies considerably, but the number of lightning days does not, and (3) the time of lightning initiation and maxima varies by elevation, with higher mountain elevations experiencing most activity 1 h before lower mountain elevations, and 3 h before lower Great Plains locations.  相似文献   

12.
Landscape pattern is an important determinant of soil contamination at multiple scales, and a proper understanding of their relationship is essential for alleviating soil contamination and making decisions for land planners. Both soil contamination and landscape patterns are heterogeneous across spaces and scale-dependent, but most studies were carried out on a single scale and used the conventional multivariate analyses (e.g. correlation analysis, ordinary least squared regression-OLS) that ignored the issue of spatial autocorrelation. To move forward, this paper examined spatially varying relationships between agricultural soil trace metal contamination and landscape patterns at three block scales (i.e. 5 km × 5  km, 10 km × 10 km, 15 km × 15 km) in the Pearl River Delta (PRD), south China, using geographically weighted regression (GWR). This paper found that GWR performed better than OLS in terms of increasing R square of the model, lowering Akaike Information Criterion values and reducing spatial autocorrelation. GWR results revealed great spatial variations in the relationships across scales, with an increasing explanatory power of the model from small to large block scales. Despite a few negative correlations, more positive correlations were found between soil contamination and different aspects of landscape patterns of water, urban land and the whole landscape (i.e. the proportion, mean patch area, the degree of landscape fragmentation, landscape-level structural complexity, aggregation/connectivity, road density and river density). Similarly, more negative correlations were found between soil contamination and landscape patterns of forest and the distance to the river and industry land (p < 0.05). Furthermore, most significant correlations between soil contamination and landscape variables occurred in the western PRD across scales, which could be explained by the prevailing wind, the distribution of pollutant sources and the pathway of trace metal inputs.  相似文献   

13.
ABSTRACT

The aim of site planning based on multiple viewshed analysis is to select the minimum number of viewpoints that maximize visual coverage over a given terrain. However, increasingly high-resolution terrain data means that the number of terrain points will increase rapidly, which will lead to rapid increases in computational requirements for multiple viewshed site planning. In this article, we propose a fast Candidate Viewpoints Filtering (CVF) algorithm for multiple viewshed site planning to lay a foundation for viewpoint optimization selection. Firstly, terrain feature points are selected as candidate viewpoints. Then, these candidate viewpoints are clustered and those belonging to each cluster are sorted according to the index of viewshed contribution (IVC). Finally, the candidate viewpoints with relatively low viewshed contribution rate are removed gradually using the CVF algorithm, through which, the viewpoints with high viewshed contribution are preserved and the number of viewpoints to be preserved can be controlled by the number of clusters. To evaluate the effectiveness of our CVF algorithm, we compare it with the Region Partitioning for Filtering (RPF) and Simulated Annealing (SA) algorithms. Experimental results show that our CVF algorithm is a substantial improvement in both computational efficiency and total viewshed coverage rate.  相似文献   

14.
Small, shallow, temperate lakes are predominant landscape features in North America, however, little is known about their long-term ecosystem dynamics, and few data exist on the chironomid fauna they harbor. Using multivariate analyses, we defined relationships between sub-fossil chironomid assemblage composition and environmental variables in 26 shallow lakes of northeastern USA and quantified how differences in taxonomic resolution affect transfer function model performance. Using redundancy analysis, we found that chironomid assemblages are best explained by turbidity, dissolved inorganic carbon and drainage basin/lake area ratio. Turbidity explained the greatest proportion of variance found in the chironomid assemblage (10.4%), followed by total nitrogen. Through ordination analyses and an analysis of similarity, we found that macrophyte density was also a significant predictor of chironomid assemblages. We used partial least squares analysis to develop a robust model for quantitative reconstruction of turbidity, with r jack2 = 0.62. When using a more coarsely resolved taxonomic dataset, we found that model performance statistics were weaker, suggesting the need for fine-resolution taxonomy. Overall, our findings highlight the importance of variables related to lake trophic state in structuring chironomid assemblages in shallow, temperate lakes and provide tools for inferring past ecological changes in these ecosystems.  相似文献   

15.
伊犁河三角洲景观结构的影响机制研究   总被引：1，自引：0，他引：1  
在遥感和水文数据的支持下,根据伊犁河三角洲作为典型的中亚干旱区内陆河流域尾闾区域特点,确定了伊犁河三角洲的景观分类系统。通过采用景观结构梯度分析法、景观干扰度指数和景观Kappa指数等方法,系统地分析了近32 a（1975-2007）伊犁河三角洲景观结构的时空演变特征,并对景观结构的影响机制做了充分地探讨。结果表明：（1）沿着一定的地形梯度和水文梯度,伊犁河三角洲流域景观表现出特殊的纵向结构、横向结构的梯度特征和景观内部特征,与地表水直接关联的景观类型表现尤为明显,如湖泊、沼泽、漫滩。（2）在人为活动和自然环境的双重影响下,近32 a伊犁河三角洲景观结构的空间变化具有一定的周期性和不稳定性,主要体现为景观类型面积和空间位置的变化,其中以湿地景观类型的变化最为显著。（3）生态干扰对景观结构的影响因景观类型的不同存在显著的差异性和时空变异性,以湖泊和沼泽受干扰作用最为明显。高、中、低三种干扰强度区域的空间分布及面积变化同样具有一定的周期性和不稳定性。（4）水利工程建设和自然环境是影响伊犁河三角洲景观结构的主要驱动力。水利工程对伊犁河的拦蓄引起景观结构变化的作用最为深远,它通过改变三角洲上游的水文情势直接影响整个区域的景观结构。而自然环境因素中的地形和水文条件主要影响湿地景观类型的时空分布,气候因子则直接影响河川径流量。  相似文献   

16.
快速城市化地区景观组分在地形梯度上的分布特征研究   总被引：65，自引：5，他引：65  
喻红  曾辉  江子瀛 《地理科学》2001,21(1):64-69
采用地形位指数综合描述深圳市龙华地区的地形差异，并在此基础上，利用无量纲的分布指数对景观组分的空间分布特征进行了半定量分析，结果表明，地形位指数可以综合地反映地形条件的空间分布和差异信息，分布指数用于描述某各组分的实际分布与标准分布的差异，可以排险面积的干扰，为各种经较分析创造了条件，研究时段内龙华地区景观组分在地形位梯度上整体分布格局的复杂性显著增加，人为景观改造活动主要表现为一种中尺度土地利用结构调整行为，并有助于对不同地形条件下的土地利用进行加严格的分工，地形差异则是大尺度景观整体格局形成的基本骨架。  相似文献   

17.
We demonstrate the use of Fourier transform infrared spectroscopy (FTIRS) to make quantitative measures of total organic carbon (TOC), total inorganic carbon (TIC) and biogenic silica (BSi) concentrations in sediment. FTIRS is a fast and cost-effective technique and only small sediment samples are needed (0.01 g). Statistically significant models were developed using sediment samples from northern Sweden and were applied to sediment records from Sweden, northeast Siberia and Macedonia. The correlation between FTIRS-inferred values and amounts of biogeochemical constituents assessed conventionally varied between r = 0.84–0.99 for TOC, r = 0.85–0.99 for TIC, and r = 0.68–0.94 for BSi. Because FTIR spectra contain information on a large number of both inorganic and organic components, there is great potential for FTIRS to become an important tool in paleolimnology.  相似文献   

18.
The fjord landscape of South America, stretching ~ 1500 km between Golfo Corcovado (~ 43°S) and Tierra del Fuego (~ 56°S), is the largest continuous fjord landscape on Earth. This paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models. First-order geological structures are represented by strike-slip faults forming lineaments up to hundreds of kilometres long. The strike-slip faulting has been active since Late Cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to ~ 10 km long. A detailed analysis of these second-order lineaments from digital image data was carried out in three sectors. In Sector 1, located northwest of the North Patagonian Icefield, there are three distinct mean orientations, characterized by a main nearly orogen-parallel orientation (az. ~ 145°) and two orogen-oblique secondary orientations (az. ~ 20° and az. ~ 65°). In Sector 2, located west of the South Patagonian Icefield, there are also three separate mean orientations, with most of the lineaments concentrated between azimuths 0° and 80° (mean at ~ 36°); and two other orogen-oblique means at azimuth ~ 122° and ~ 163°. In Sector 3, around the Cordillera Darwin, there is a single main orogen-parallel mean at ~ 100–115°. In all three sectors, mapped fjord orientations bear a striking similarity to the structural data, with fjords orientated preferentially in the same direction as structural lineaments. We infer that successive glaciations followed the same ice-discharge routes, widening and deepening pre-existing geological structures at the expense of the surrounding terrain to create the fjord landscape. This study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological.  相似文献   

19.
刘前进  于兴修 《地理研究》2010,29(8):1471-1483
以具北方土石山区典型特征的沂蒙山区为例,在分析土壤侵蚀过程的基础上,选取具生态学意义的侵蚀强度景观格局指数,从垂直维度上分析侵蚀景观格局变化特征。结果表明:土壤侵蚀景观格局具有显著垂直分带性。50~200带为低侵蚀稳定区,人类活动影响大,缀块成片分布,连通性强,形状较规则;400~800带为高侵蚀稳定区,自然因素起主导作用,缀块密度大且分散,形状较复杂;200~400带为侵蚀景观急剧变化区,侵蚀程度随高程增加而增大,自然因素作用增强。微度与轻度侵蚀景观、强烈与极强烈侵蚀景观具相同垂直变化趋势,此两组侵蚀景观变化趋势的差异主要分布于低于300带和高于500带处;中度侵蚀景观变化趋势可视为前两组侵蚀景观变化趋势的过渡。  相似文献   

20.
以三工河流域为例,讨论了荒漠绿洲植被变化与景观格局的耦合关系.结果表明:(1)荒漠绿洲景观格局最明显的特征是植被变化,其通过地貌、水资源利用、河流廊道或排碱渠等景观要素的变化对植被产生影响;随着景观格局的变化,流域内的植丛高度、盖度及生物量均表现出较大变异性.(2)以河流廊道为核心,通常荒漠绿洲景观格局呈带状分布且由内向外,随水热条件的改变,植被类型由乔灌木林依次向灌丛草甸、盐化草甸、荒漠化草甸和荒漠层次结构过渡.(3)人类活动影响强烈的景观要素,其缀块多样性、破碎度、分离度和缀块密度等指数的值较高,而人类活动影响较小的,其优势度和均匀度较高.(4)各景观要素的稳定性不同,通常自然缀块的稳定性高于人工缀块,其排序为:荒漠>砾石地、沙地>城镇工矿用地>水体>灌溉水田>牧草地>菜地>林地>农村居民点>盐碱地>荒草地>水浇地>果园.  相似文献   

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