出租车GPS轨迹集聚和精细化路网提取

针对利用GPS数据提取双向路网和交叉路口转向信息精度低的不足,本文提出一种顾及位置与行驶方向的轨迹集聚和精细化路网提取方法,实现了精细化路网提取。为提高交叉路口路网的提取精度,首先剔除原始轨迹中的离散和异常轨迹点,并按一定的步长对轨迹段进行加密;然后引入行驶方向角来表达车辆在轨迹点处的行驶方向,顾及位置和行驶方向获取每个轨迹点的相似轨迹点集合;接着依次计算每个轨迹点的偏移距离,通过对轨迹点的迭代偏移完成轨迹集聚;最后剔除未成功集聚的轨迹点,将完成集聚的轨迹点连成轨迹线并作缓冲区,运用栅格数据数字化方法提取得到能够反映道路精细转向关系的道路网。以福州市出租车GPS数据进行轨迹集聚和路网提取试验,结果表明:本文方法能有效地将GPS轨迹按车辆行驶方向分别进行集聚,提取的道路网为双向道路并且能反映交叉路口处道路的精细转向关系。     

Catchment‐scale contribution of forest roads to stream exports of sediment,phosphorus and nitrogen

The relative contribution of forest roads to total catchment exports of suspended sediment, phosphorus, and nitrogen was estimated for a 13 451 ha forested catchment in southeastern Australia. Instrumentation was installed for 1 year to quantify total in‐stream exports of suspended sediment, phosphorus, and nitrogen. In addition, a total of 101 road–stream crossings were mapped and characterized in detail within the catchment to identify the properties of the road section where the road network and the stream network intersect. Sediment and nutrient generation rates from different forest road types within the catchment were quantified using permanent instrumentation and rainfall simulation. Sediment and nutrient generation rates, mapped stream crossing information, traffic data and annual rainfall data were used to estimate annual loads of sediment, phosphorus, and nitrogen from each stream crossing in the catchment. The annual sum of these loads was compared with the measured total catchment exports to estimate the proportional contribution of loads from roads within the catchment. The results indicated that 3·15 ha of near‐stream unsealed road surface with an average slope of 8·4% delivered an estimated 50 t of the 1142 t of total suspended sediment exported from the catchment, or about 4·4% of the total sediment load from the forest. Stream discharge over this period was 69 573 Ml. The unsealed road network delivered an estimated maximum of 22 kg of the 1244 kg of total phosphorus from the catchment, or less than 1·8% of the total load from the forest. The average sediment and phosphorous load per crossing was estimated at 0·5 t (standard deviation 1·0 t) and 0·22 kg (standard deviation 0·30 kg) respectively. The lower proportional contribution of total phosphorus resulted from a low ratio of total phosphorus to total suspended sediment for the road‐derived sediment. The unsealed road network delivered approximately 33 kg of the 20 163 kg of total nitrogen, about 0·16% of the total load of nitrogen from the forest. The data indicate that, in this catchment, improvement of stream crossings would yield only small benefits in terms of net catchment exports of total suspended sediment and total phosphorus, and no benefit in terms of total nitrogen. These results are for a catchment with minimal road‐related mass movement, and extrapolation of these findings to the broader forested estate requires further research. Copyright © 2007 John Wiley & Sons, Ltd.     

基于气象监测网络的森林火险快速预警模型

森林火灾发生频繁且突发性强,进行森林火险快速预警对于减小森林火灾损失和促进森林资源可持续发展至关重要。本文基于GIS空间分析和可视化技术,利用地面气象站构建实时气象监测网络,设计了运用气象监测网络的森林火险预警模型,可实现森林火险及时、快速预警。模型应用层次分析法建立了预警因子重要性层次结构并确定预警因子的权重;运用Voronoi图技术,基于气象站点和实时气象数据,构建气象监测网络;利用叠置分析技术计算得出预警结果。基于该模型设计的森林火灾快速预警系统应用于青海省林业局,验证了系统可行性与适用性,该模型可全面、准确、快速地实现对森林火险的预警。结果表明：① 根据预警模型及实时气象监测数据,可及时发出预警信号,快速实现县级、林场级别的森林火险早期预警和及时响应;② 运用GIS可视化技术,可快速生成相关区域森林火险的空间分布专题图,直观地观察预警等级的变化情况。实践表明,森林火险快速预警对森林火灾进行有效预防、中断管理和制定扑救措施具有重要的指导作用,并对森林防火工作、保护森林资源和人类生命财产安全具有重大意义。     

Analysis of behaviour of vehicles using VGI data

This article describes a methodology for analysing the behaviour of vehicles on roads using data obtained from Volunteered Geographic Information and more specifically from GNSS traces. These data have a great potential for this goal due to their distribution, continuity and anonymity. The proposed methodology includes all possible stages, from traces selection and downloading, passing by filtering, matching and enrichment using official linestrings, to the final obtaining of results. The article also shows the main results obtained after applying this methodology to a real case that uses a large quantity of traces, distributed over a large zone of study, including several types of roads and conditions. These results allow us to analyse the behaviour of the implicated vehicles based on the speed and the acceleration or deceleration of each trackpoint which composes the traces and compare them with the general official data published by the traffic authorities. The analysis of the results has demonstrated the viability of this methodology and its possible implementation by traffic authorities in order to obtain information to improve traffic safety.     

利用模板匹配和BSnake算法准自动提取遥感影像面状道路

针对已有的遥感影像面状道路提取策略在自动化程度、效率及精度方面的不足,提出了一种新的快速有效的准自动提取方法。遥感影像上各种面状道路的提取实验证明了算法的有效性,在自动化程度、速度和精度上均有明显成效。     

THE NINETEENTH‐CENTURY EVOLUTION OF LOCAL‐SCALE ROADS IN KENTUCKY'S BLUEGRASS

ABSTRACT. In the nineteenth century, local‐scale roads in central Kentucky were built subject to local knowledge and cultural tradition but within the context of legal authority and folk‐ or science‐based engineering precepts. This study demonstrates how legal and engineering standards‐though conceived as transcendent and objective‐were in fact contingent on the region's physical attributes as well as its cultural traditions and character. Thus local road alignment and construction have been influenced by and contingent on local knowledge, dialogue, and debate since frontier times.     

The concept of hydrological connectivity and its contribution to understanding runoff‐dominated geomorphic systems

The term ‘connectivity’ is increasingly being applied in hydrological and geomorphological studies. Relevant research encompasses aspects of landscape connectivity, hydrological connectivity and sedimentological connectivity. Unlike other disciplines, notably ecology, published studies show no consensus on a standard definition. This paper provides an overview of how existing research relates to the concept of connectivity in both ecology and hydrology by proposing and evaluating a conceptual model of hydrological connectivity that includes five major components: climate; hillslope runoff potential; landscape position; delivery pathway and lateral connectivity. We also evaluate a proposed measure of connectivity called the volume to breakthrough to quantify changing connectivity between different environments and catchments. Copyright © 2007 John Wiley & Sons, Ltd.     

A methodology to assess the delivery of road runoff in forestry environments

This paper outlines a conceptual and methodological approach to evaluating the risk of road derived runoff delivery, which is based on the principle of hydrological connectivity. Three different types of runoff delivery pathways are identified (stream crossings, gullied pathways and diffuse pathways) and the volume of runoff that may reach the stream through these pathways during a one in 10 year 30 minute event is estimated. The methodology is applied to three catchments of contrasting forest use, both plantation and native. Results show that degree of connectivity of a road depends on catchment characteristics such as the topography, road placement, drain spacing and road and drainage density. Maps outlining the distribution of different delivery pathways within a catchment are used to assess the potential for runoff connectivity. In one of the selected study catchments, the Albert River, greatest potential connectivity can be isolated to a single road. The upper part of this road crosses many tributaries resulting in high connectivity via stream crossings, whereas the lower part of the road is located within the valley bottom, where the majority of drains will contribute runoff during a one in 10 year event through diffuse overland flow. The presented methodology is also used to highlight hot‐spots in terms of runoff and sediment delivery through the creation of risk assessment maps, which allows for the evaluation of different procedures for road rehabilitation. Using examples from the Albert River catchment, we demonstrate that minimizing diffuse overland flow can generally be achieved by the placement of additional road drains, whereas at highly connected road segments the relocation of the road might be the only option. Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling plumes of overland flow from logging tracks

Most land‐based forestry systems use extensive networks of unsealed tracks to access the timber resource. These tracks are normally drained by constructing cross‐banks, or water bars, across the tracks immediately following logging. Cross‐banks serve three functions in controlling sediment movement within forestry compartments:

• 1. they define the specific catchment area of the snig track (also known as skid trails) so that the overland flow does not develop sufficient energy to cause gullies, and sheet and rill erosion is reduced;
• 2. they induce some sediment deposition as flow velocity reduces at the cross‐bank;
• 3. they redirect overland flow into the adjacent general harvesting area (GHA) so that further sediment deposition may take place.

This paper describes a simple model that predicts the third of these functions in which the rate of runoff from the track is combined with spatial attributes of the track and stream network. Predictions of the extent of the overland flow plumes and the volume of water delivered to streams is probabilistically presented for a range of rainfall‐event scenarios with rainfall intensity, time since logging and compartment layout as model inputs. Generic equations guiding the trade‐off between intercross‐bank length and flow path distance from cross‐bank outlet to the stream network needed for infiltration of track runoff are derived. Copyright © 2002 John Wiley & Sons, Ltd. Copyright © 2002 John Wiley & Sons, Ltd.