共查询到20条相似文献，搜索用时 31 毫秒
1.
《International Journal of Digital Earth》2013,6(12):1231-1252
ABSTRACTOfficial warnings are essential for informing the public of impending hazards and promoting their responses before a disaster occurs. However, research has identified that traditional public warnings, such as generic text messages based on large geographic regions, often fail to promote appropriate responses by at-risk residents. Recently, there has been an increased focus on using map-based approaches for communicating public warnings. However, a systematic framework to guide the design of effective mapping instruments for this purpose is lacking. The researchers sought to fill this gap by merging the scholarly understanding of factors influencing warning effectiveness with the contemporary spatial capacities of the emergency management sector. The current paper presents the conceptual framework resulting from this merger, which can be used to direct the design and implementation of map-based warnings that offer personalised risk visualisation and provide personalised decision support to motivate appropriate responses. An example is then provided to illustrate how this framework can be applied for the development of personalised bushfire warnings in an Australian context. Underpinned by webGIS technologies, the proposed framework shows a potentially ground-breaking approach to improve public warning communication by fostering more efficient and effective risk personalisation and response related decision-making by individuals. 相似文献
2.
《测量评论》2013,45(64):52-70
AbstractIn the last instalment we were able to obtain most of the surveyor's projections in common use by applying simple scale conditions to the meridians and parallels. This method of approach naturally suggests that results of some value might be obtained by applying similar conditions to the plane co-ordinate lines. If we do so, we are immediately led to consider curves on the surface known as geodesics, which are the nearest approach to straight lines it is possible to draw on a curved surface. Accordingly, we give some account of these curves for the benefit of surveyors who have not hitherto made their acquaintance. 相似文献
3.
ADCN: An anisotropic density‐based clustering algorithm for discovering spatial point patterns with noise 
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下载免费PDF全文 Density‐based clustering algorithms such as DBSCAN have been widely used for spatial knowledge discovery as they offer several key advantages compared with other clustering algorithms. They can discover clusters with arbitrary shapes, are robust to noise, and do not require prior knowledge (or estimation) of the number of clusters. The idea of using a scan circle centered at each point with a search radius Eps to find at least MinPts points as a criterion for deriving local density is easily understandable and sufficient for exploring isotropic spatial point patterns. However, there are many cases that cannot be adequately captured this way, particularly if they involve linear features or shapes with a continuously changing density, such as a spiral. In such cases, DBSCAN tends to either create an increasing number of small clusters or add noise points into large clusters. Therefore, in this article, we propose a novel anisotropic density‐based clustering algorithm (ADCN). To motivate our work, we introduce synthetic and real‐world cases that cannot be handled sufficiently by DBSCAN (or OPTICS). We then present our clustering algorithm and test it with a wide range of cases. We demonstrate that our algorithm can perform equally as well as DBSCAN in cases that do not benefit explicitly from an anisotropic perspective, and that it outperforms DBSCAN in cases that do. Finally, we show that our approach has the same time complexity as DBSCAN and OPTICS, namely O(n log n) when using a spatial index and O(n2) otherwise. We provide an implementation and test the runtime over multiple cases. 相似文献
4.
An Assessment of the RAIM Performance of a Combined Galileo/GPS Navigation System Using the Marginally Detectable Errors (MDE) Algorithm 总被引：1，自引：0，他引：1
W. Y. Ochieng K. F. Sheridan K. Sauer X. Han P. A. Cross S. Lannelongue N. Ammour K. Petit 《GPS Solutions》2002,5(3):42-51
Integrity relates to the trust that can be placed in the correctness of information supplied by a navigation system. It includes
the ability of the navigation system to provide timely warning to users when the system fails to meet its stated accuracy.
Specifically, a navigation system is required to deliver a warning (alarm) when the error in the derived user position solution exceeds an allowable level (alarm limit). This warning must be issued to the user within a given period of time (time-to-alarm) and with a given probability (integrity risk). The two main approaches to monitoring the integrity of satellite navigation systems are Receiver Autonomous Integrity Monitoring
(RAIM), and monitoring based on an independent network of integrity monitoring stations and a dedicated Ground Integrity Channel
(GIC). More recently Satellite Autonomous Integrity Monitoring (SAIM) methods have also been investigated.
This article presents the results of a study to assess the RAIM capability of the Galileo system when used alone and when
combined with the Global Positioning System (GPS). The assessment was based on the Marginally Detectable Error (MDE) algorithm.
The results show a significant improvement in the capability to perform RAIM using a combined Galileo/GPS system compared
to the performance using the Galileo system alone. This study was supported by Alcatel Space and was a contribution to the
Galileo definition studies carried out for the European Community under the GALA project. ? 2002 Wiley Periodicals, Inc. 相似文献
5.
6.
《地理信息系统科学与遥感》2013,50(6):895-914
Vegetation type is an environmental attribute that varies across the landscape and over time. Its continuous assessment is important for monitoring land use changes and forest degradation. There are advanced methods that can estimate the fractional cover of vegetation types within each pixel. This paper compares some methods for subpixel mapping of forest cover in the state of San Luis Potosí, Mexico, using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived spectral data (MCD43A4). Three methods were tested: (1) Bayesian posterior probability, (2) the Fuzzy k nearest neighbor (FkNN), and (3) linear spectral mixture analysis (LSMA). While the Bayesian approach gave the poorest correlations, FkNN (r = 0.78) and LSMA (r = 0.81) estimations were successfully validated with information obtained from a Landsat image. This paper represents an interesting attempt to compare rarely reported FkNN with traditional approaches such as LSMA and the Bayesian one. 相似文献
7.
Social media messages, such as tweets, are frequently used by people during natural disasters to share real‐time information and to report incidents. Within these messages, geographic locations are often described. Accurate recognition and geolocation of these locations are critical for reaching those in need. This article focuses on the first part of this process, namely recognizing locations from social media messages. While general named entity recognition tools are often used to recognize locations, their performance is limited due to the various language irregularities associated with social media text, such as informal sentence structures, inconsistent letter cases, name abbreviations, and misspellings. We present NeuroTPR, which is a Neuro‐net ToPonym Recognition model designed specifically with these linguistic irregularities in mind. Our approach extends a general bidirectional recurrent neural network model with a number of features designed to address the task of location recognition in social media messages. We also propose an automatic workflow for generating annotated data sets from Wikipedia articles for training toponym recognition models. We demonstrate NeuroTPR by applying it to three test data sets, including a Twitter data set from Hurricane Harvey, and comparing its performance with those of six baseline models. 相似文献
8.
Masashi Miyagawa 《Journal of Geographical Systems》2012,14(2):209-222
This paper derives the joint distribution of the distances to the first and the second nearest points for regular and random
patterns. Distance is measured as the Euclidean and the rectilinear distances on a continuous plane. The joint distribution
extends the kth nearest distance distribution of previous works. The kth nearest distance distribution only shows how the distance to the kth nearest point is distributed, whereas the joint distribution provides the relationship between the distances. An application
of the joint distribution can be found in a facility location problem with non-closest facility service where the distance
to the second nearest facility is also important. The joint distribution that allows us to examine the first and the second
nearest distances simultaneously is useful for evaluating the reliability of facility location when some of the existing facilities
are closed. The joint distribution of the road network distances is also obtained to confirm that the model on a continuous
plane can be applied to actual road networks. 相似文献
9.
《测量评论》2013,45(16):66-71
Abstract(I) The deserts of India and Baluchistan.—In the eastern half of the Great Indian Desert there are rock-outcrops projecting above the sand at in tervals averaging twenty miles; these have been landmarks for travellers for centuries, and consequently they all have native names. In the western desert there are no outcrops and no objects to name; but the desert nomads and the camel-breeders do have names for vague undefined areas, which seem to move as the sandhills move. The rock-outcrops in Baluchistan are larger and more numerous, and many are consequently without Baluchi names. Nothing would have been gained from inventing names; names are for use, not for show, and the desert people know their own requirements. It is better on a map to limit the nomenclature to the names that have been born of the people and that have stood the test of time than to supplement them with fictitious names. Survey stations on unnamed hills are therefore generally designated by symbols such as B45. 相似文献
10.
11.
Big location‐based social media messages from China's Sina Weibo network: Collection,storage, visualization,and potential ways of analysis 下载免费PDF全文
下载免费PDF全文 China's social media platform, Sina Weibo, like Twitter, hosts a considerable amount of big data: messages, comments, pictures. Collecting and analyzing information from this treasury of human behavior data is a challenge, although the message exchange on the network is readable by everyone through the web or app interface. The official Application Programming Interface (API) is the gateway to access and download public content from Sina Weibo and is used to collect messages for all mainland China. The nearby_timeline() request is used to harvest only messages with associated location information. This technical note serves as a reference for researchers who do not speak Mandarin but want to collect data from this rich source of information. Ways of data visualization are presented as a point cloud, density per areal unit, or clustered using Density‐Based Spatial Clustering of Applications with Noise (DBSCAN). The relation of messages to census information is also given. 相似文献
12.
A data archive of GPS navigation messages 总被引：2，自引：1，他引：1
Since 18 June 2007 navigation data messages transmitted by the GPS constellation are recorded by five receivers within GeoForschungsZentrum’s
global groundstation network. We describe the recording, processing, validation, analysis and archiving of the navigation
data. During the 197 days between 18 June 2007 and 31 December 2007 a total of 125,723,666 subframes were collected. By taking
into consideration that the same data set frequently is observed by two or more receivers concurrently, 65,153,955 unique
subframes could be extracted from the observations. With an estimated 88,099,200 subframes transmitted by the constellation
during this time period a data yield of about 74% was achieved. Simulation studies suggest that with two additional GPS receivers,
which are scheduled for addition to the network in 2008, about 95% of the transmitted subframes will be retrieved. The message
data archive is open to the scientific community for non-commercial purposes and may be accessed through GFZ’s Information
System and Data Center ().
相似文献
| G. BeyerleEmail: |
13.
Testing for similarity in area‐based spatial patterns: Alternative methods to Andresen's spatial point pattern test 下载免费PDF全文
下载免费PDF全文 Andresen's spatial point pattern test (SPPT) compares two spatial point patterns on defined areal units; it identifies areas where the spatial point patterns diverge and aggregates these local (dis)similarities to one global measure. We discuss the limitations of the SPPT and provide two alternative methods to calculate differences in the point patterns. In the first approach we use differences in proportions tests corrected for multiple comparisons. We show how the size of differences matters, as with large point patterns many areas will be identified by SPPT as statistically different, even if those differences are substantively trivial. The second approach uses multinomial logistic regression, which can be extended to identify differences in proportions over continuous time. We demonstrate these methods by identifying areas where pedestrian stops by the New York City Police Department are different from violent crimes for 2006–2016. 相似文献
14.
Geocoding systems typically use more than one geographic reference dataset to improve match rates and spatial accuracy, resulting in multiple candidate geocodes from which the single “best” result must be selected. Little scientific evidence exists for formalizing this selection process or comparing one strategy to another, leading to the approach used in existing systems which we term the hierarchy‐based criterion: place the available reference data layers into qualitative, static, and in many cases, arbitrary hierarchies and attempt a match in each layer, in order. The first non‐ambiguous match with suitable confidence is selected and returned as output. This approach assumes global relationships of relative accuracy between reference data layers, ignoring local variations that could be exploited to return more precise geocodes. We propose a formalization of the selection criteria and present three alternative strategies which we term the uncertainty‐, gravitationally‐, and topologically‐based strategies. The performance of each method is evaluated against two ground truth datasets of nationwide GPS points to determine any resulting spatial improvements. We find that any of the three new methods improves on current practice in the majority of cases. The gravitationally‐ and topologically‐based approaches offer improvement over a simple uncertainty‐based approach in cases with specific characteristics. 相似文献
15.
none 《The Cartographic journal》2013,50(1):49-60
AbstractMany of the traditional data visualization techniques, which proved to be supportive for exploratory analysis of datasets of moderate sizes, fail to fulfil their function when applied to large datasets. There are two approaches to coping with large amounts of data: data selection, when only a portion of data is displayed, and data aggregation, i.e. grouping data items and considering the groups instead of the original data. None of these approaches alone suits the needs of exploratory data analysis, which requires consideration of data on all levels: overall (considering a dataset as a whole), intermediate (viewing and comparing collective characteristics of arbitrary data subsets, or classes), and elementary (accessing individual data items). Therefore, it is necessary to combine these approaches, i.e. build a tool showing the whole set and arbitrarily defined subsets (object classes) in an aggregated way and superimposing this with a representation of arbitrarily selected individual data items.We have achieved such a combination of approaches by modifying the technique of parallel coordinate plot. These modifications are described and analysed in the paper. 相似文献
16.
Geoffrey J. Hay Guillermo Castilla Michael A. Wulder Jose R. Ruiz 《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):339-359
Over the last decade the analysis of Earth observation data has evolved from what were predominantly per-pixel multispectral-based approaches, to the development and application of multiscale object-based methods. To empower users with these emerging object-based approaches, methods need to be intuitive, easy to use, require little user intervention, and provide results closely matching those generated by human interpreters. In an attempt to facilitate this, we present multiscale object-specific segmentation (MOSS) as an integrative object-based approach for automatically delineating image-objects (i.e., segments) at multiple scales from a high-spatial resolution remotely sensed forest scene. We further illustrate that these segments cognitively correspond to individual tree crowns, ranging up to forest stands, and describe how such a tool may be used in computer-assisted forest inventory mapping. MOSS is composed of three primary components: object-specific analysis (OSA), object-specific upscaling (OSU), and a new segmentation algorithm referred to as size constrained region merging (SCRM). The rationale for integrating these methods is that the first two provide the third with object-size parameters that otherwise would need to be specified by a user. Analysis is performed on an IKONOS-2 panchromatic image that represents a highly fragmented forested landscape in the Sooke Watershed on southern Vancouver Island, BC, Canada. 相似文献
17.
The paper proposes an upgraded landmark-Isometric mapping (UL-Isomap) method to solve the two problems of landmark selection and computational complexity in dimensionality reduction using landmark Isometric mapping (LIsomap) for hyperspectral imagery (HSI) classification. First, the vector quantization method is introduced to select proper landmarks for HSI data. The approach considers the variations in local density of pixels in the spectral space. It locates the unique landmarks representing the geometric structures of HSI data. Then, random projections are used to reduce the bands of HSI data. After that, the new method incorporates the Recursive Lanczos Bisection (RLB) algorithm to construct the fast approximate k-nearest neighbor graph. The RLB algorithm accompanied with random projections improves the speed of neighbor searching in UL-Isomap. After constructing the geodesic distance graph between landmarks and all pixels, the method uses a fast randomized low-rank approximate method to speed up the eigenvalue decomposition of the inner-product matrix in multidimensional scaling. Manifold coordinates of landmarks are then computed. Manifold coordinates of non-landmarks are computed through the pseudo inverse transformation of landmark coordinates. Five experiments on two different HSI datasets are run to test the new UL-Isomap method. Experimental results show that UL-Isomap surpasses LIsomap, both in the overall classification accuracy (OCA) and in computational speed, with a speed over 5 times faster. Moreover, the UL-Isomap method, when compared against the Isometric mapping (Isomap) method, obtains only slightly lower OCAs. 相似文献
18.
青藏高原小嵩草高寒草甸返青期遥感识别方法筛选 总被引：3，自引：1，他引：2
小嵩草高寒草甸是青藏高原的主要植被类型,研究其返青期识别方法对于模拟及预测青藏高原植被物候变化具有重要意义。常用的植被返青期遥感识别方法主要是先对遥感植被指数原始时序数据进行拟合去噪声再求取返青期,各种方法对研究区域、研究经验、参数设置、函数初值设置等有很强的依赖性。为避免返青期识别方法在曲线拟合时对参数初值的依赖性和陷入局部最优解,本文引入了模拟退火算法对双高斯和双逻辑斯蒂函数进行参数优化,并分别对基于以上两种函数及多项式拟合的植被指数时序曲线进行对比,从而选出最佳拟合方法,最后采用最大斜率阈值法、动态阈值法和曲率法识别返青期。利用青藏高原小嵩草高寒草甸34个样本点的返青期地面观测数据及相应的8 km分辨率的NOAA归一化差值植被指数(NDVI)时序数据对以上各种组合的返青期遥感识别方案进行了测试,并选取了153个遥感实验点求取了近30年(1982年—2011年)青藏高原小嵩草高寒草甸的返青期,结果表明:采用双高斯函数拟合的NDVI曲线与原始NDVI时序数据最为接近,在此基础上采用最大斜率阈值法识别的小嵩草高寒草甸返青期及其变化趋势与地面物候观测结果最为一致;同时发现近30年青藏高原小嵩草高寒草甸的平均返青期主要集中在每年的第120—140天,并且呈逐年提前趋势,30年来提前了7天。 相似文献
19.
In Geographic Information Systems (GIS), geoprocessing workflows allow analysts to organize their methods on spatial data in complex chains. We propose a method for expressing workflows as linked data, and for semi-automatically enriching them with semantics on the level of their operations and datasets. Linked workflows can be easily published on the Web and queried for types of inputs, results, or tools. Thus, GIS analysts can reuse their workflows in a modular way, selecting, adapting, and recommending resources based on compatible semantic types. Our typing approach starts from minimal annotations of workflow operations with classes of GIS tools, and then propagates data types and implicit semantic structures through the workflow using an OWL typing scheme and SPARQL rules by backtracking over GIS operations. The method is implemented in Python and is evaluated on two real-world geoprocessing workflows, generated with Esri's ArcGIS. To illustrate the potential applications of our typing method, we formulate and execute competency questions over these workflows. 相似文献
20.
Identifying local spatial association in flow data 总被引：5，自引：1，他引：4
In this paper we develop a spatial association statistic for flow data by generalizing the statistic of Getis-Ord, G
i (and G
i
*). This local measure of spatial association, G
ij, is associated with each origin-destination pair. We define spatial weight matrices with different metrics in flow space.
These spatial weight matrices focus on different aspects of local spatial association. We also define measures which control
for generation or attraction nonstationarity. The measures are implemented to examine the spatial association of residuals
from two different models. Using the permutation approach, significance bounds are computed for each statistic. In contrast
to the G
i statistic, the normal approximation is often appropriate, but the statistics are still correlated. Small sample properties
are also briefly discussed.
Received: 18 February 1998/Accepted: 29 September 1998 相似文献