摘要:

GIS research has a continuing thread devoted to classifying the operations performed by analytical software. Prior efforts to classify GIS operations have limitations and inconsistencies, often arising from an attempt to establish overly direct links between geographic procedures and arithmetical operations. The transformational view of cartography provides a more solid basis for classifying GIS operations. This paper presents a new scheme for geographical transformations based on measurement frameworks as the principal distinction. Transformations between measurement frameworks can be summarized in terms of a spatial neighbourhood and a rule to process attribute information. This scheme organizes most analytical GIS operations by their geometric and attribute assumptions.

ISSN:1365-8816    

DOI:10.1080/136588199241030

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spatial joins are join operations that involve spatial data types and operators. Spatial access methods are often used to speed up the computation of spatial joins. This paper addresses the issue of benchmarking spatial join operations. For this purpose, we first present a WWW-based benchmark generator to produce sets of rectangles. Using a Web browser, experimenters can specify the number of rectangles in a sample, as well as the statistical distributions of their sizes, shapes, and locations. Second, using the generator and a well-defined set of statistical models we define several tests to compare the performance of three spatial join algorithms: nested loop, scan-and-index, and synchronized tree traversal. We also added two real-life data sets from the Sequoia 2000 storage benchmark. Our results show that the relative performance of the different techniques mainly depends on the selectivity factor of the join predicate. All of the statistical models and algorithms are available on the Web, which allows for easy verification and modification of our experiments.

ISSN:1365-8816    

DOI:10.1080/136588199241049

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

It has been recently recognized that fuzzy set theory provides useful concepts and tools for both the representation and analysis of the uncertainty related to geographical data. Hence the incorporation of fuzzy set methodologies into a DBMS repository for the application domain of GIS should be beneficial and will improve its level of intelligence. Focusing in this area the paper addresses both a representation and a reasoning issue. Specifically, it extends a general spatial data model to deal with the uncertainty of geographical entities, and shows how the standard data interpretation operations available in GIS packages may be extended to support the fuzzy spatial reasoning. Representative geographical operations, suchas the fuzzy overlay, fuzzy distance and fuzzy select, are examined, while several real world examples are given.

ISSN:1365-8816    

DOI:10.1080/136588199241058

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A geostatistical methodology is proposed for integrating elevation estimates derived from digital elevation models (DEMs) and elevation measurements of higher accuracy, e.g., elevation spot heights. The sparse elevation measurements (hard data) and the abundant DEM-reported elevations (soft data) are employed for modeling the unknown higher accuracy (reference) elevation surface in a way that properly reflects the relative reliability of the two sources of information. Stochastic conditional simulation is performed for generating alternative, equiprobable images (numerical models) of the unknown reference elevation surface using both hard and soft data. These numerical models reproduce the hard elevation data at their measurement locations, and a set of auto and crosscovariance models quantifying spatial correlation between data of the two sources of information at various spatial scales. From this set of alternative representations of the reference elevation, the probability that the unknown reference value is greater than that reported at each node in the DEM is determined. Joint uncertainty associated with spatial features observed in the DEM, e.g. the probability for an entire ridge existing, is also modeled from this set of alternative images. A case study illustrating the proposed conflation procedure is presented for a portion of a USGS one-degree DEM. It is suggested that maps of local probabilities for over or underestimation of the unknown reference elevation values from those reported in the DEM, and joint probability values attached to different spatial features, be provided to DEM users in addition to traditionally reported summary statistics used to quantify DEM accuracy. Such a metadata element would be a valuable tool for subsequent decision-making processes that are based on the DEM elevation surface, or for targeting areas where more accurate elevation measurements are required.

ISSN:1365-8816    

DOI:10.1080/136588199241067

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Visual impact studies often make use of Boolean viewshed maps created by standard functions implemented in most raster GIS software. The DEM is used in a deterministic way and possible inaccuracies in the DEM are neglected. Monte Carlo simulations of the errors in the digital elevation data (DEM error) can be used to test the effect of the DEM error on the calculated viewshed. Both an explorational and a quantitative method based on binomial statistics are proposed to analyse the impact of the number of simulations on the accuracy of the probabilistic visibility of a cell. The probabilistic information is used for the creation of a Boolean viewshed map with a known user's and/or producer's accuracy. The importance of this methodology is illustrated.

ISSN:1365-8816    

DOI:10.1080/136588199241076

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper advocates the use of GIS for the evaluation of the vulnerability of coastal waters and presents a method for mapping their vulnerability to algal blooms. The method incorporates probability mapping of parameters used to describe coastal waters and fuzzy sets. To allow the modelling of processes where some components cannot substitute for other components the 'no trade off' convex combination formula is proposed. The maps of vulnerability for the Gulf of Gdansk, which were created using this method, may be used to find out which rivers and water discharges play a dominant role in eutrophication.

ISSN:1365-8816    

DOI:10.1080/136588199241085

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor