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An emerging topic in the field of spatial data management is the handling of location uncertainty of spatial objects, mainly due to inaccurate measurements. The literature on location uncertainty so far has focused on modifying traditional spatial search algorithms in order to handle the impact of objects' location uncertainty on the query results. In this paper, we present the first, to the best of our knowledge, theoretical analysis that estimates the average number of false hits introduced in the results of rectangular range queries in the case of data points uniformly distributed in 2D space. Then, We relax the original distribution assumptions showing how to deal with arbitrarily distributed data points and more realistic location uncertainty distributions. The accuracy of the results of our analytical approach is demonstrated through an extensive experimental study using various synthetic and real data sets. Our proposal can be directly employed in spatial database systems in order to provide users with the accuracy of spatial query results based only on known data set and query parameters. Index Terms--Spatial databases, GIS.

Problem statement: Great attention had been paid on spatial data quality by the scientific community. This was due to the negative impact that a poor spatial data quality had on the competitiveness of an organization. On other hand, we can never obtain good quality data from a poor quality data. In this study, we demonstrate the effects of the different processing and preprocessing on the quality of spatial data. As we know each type of processing introduces errors and deformations at the original spatial data. Approach: Field applications and real samples were presented to prove the effect of data processing on data quality. We used spectrally and spatially processed satellite images which present the following areas: (i) Greater Amman area, (ii) Walla and Habisse basins. Different types of processing using different scales and resolutions were applied to field applications to evaluate the effect of scale, resolution and electronic transfer from vector to raster. Results: The vector layers extracted from these spatial data at different scales and resolutions were compared to each other. The comparison showed a great deformation in shape and value. This research demonstrates the influence of the scale, the resolution and transformation from vector to raster of spatial data base on the accuracy. Conclusion: We concluded that scale, resolution and electronic transfer have great effects on data quality. This effect should be considered in building any data base and all data base must have history file for evaluating its accuracy quality. Key words: Data quality, raster, vector, preprocessing, data acquisition, INTRODUCTION Geographical Information Systems (GIS) are computer based system that is used to store, manipulate and analyze a very wide variety of subjects and fields dealing with: Civil engineering, environment, [...]

In this paper, we introduce a family of expressive models for qualitative spatial reasoning with directions. The proposed family is based on the cognitive plausible cone-based model. We formally define the directional relations that can be expressed in each model of the family. Then, we use our formal framework to study two interesting problems: computing the inverse of a directional relation and composing two directional relations. For the composition operator, in particular, we concentrate on two commonly used definitions, namely, consistency-based and existential composition. Our formal framework allows us to prove that our solutions are correct. The presented solutions are handled in a uniform manner and apply to all of the models of the family. Index Terms--Spatial databases and GIS, cone-based directional relations, inverse and composition operators.

Information in digital libraries and information systems frequently refers to locations or objects in geographic space. Digital gazetteers are commonly employed to match the referred placenames with actual locations in information integration and data cleaning procedures. This process may fail due to missing information in the gazetteer, multiple matches, or false positive matches. We have analyzed the cases of success and reasons for failure of the mapping process to a gazetteer. Based on these, we present a statistical model that permits estimating 1) the completeness of a gazetteer with respect to the specific target area and application, 2) the expected precision and recall of one-to-one mappings of source placenames to the gazetteer, 3) the semantic inconsistency that remains in one-to-one mappings, and 4) the degree to which the precision and recall are improved under knowledge of the identity of higher levels in a hierarchy of places. The presented model is based on statistical analysis of the mapping process of a large set of placenames itself and does not require any other background data. The statistical model assumes that a gazetteer is populated by a stochastic process. The paper discusses how future work could take deviations from this assumption into account. The method has been applied to a real case. Index Terms--Data mapping, knowledge and data engineering tools and techniques, database integration, data translation.

This paper investigates temporal changes of topological relationships and thereby integrates two important research areas: First, two-dimensional topological relationships that have been investigated quite intensively and, second, the change of spatial information over time. We investigate spatio-temporal predicates, which describe developments of well-known spatial topological relationships. A framework is developed in which spatio-temporal predicates can be obtained by temporal aggregation of elementary spatial predicates and sequential composition. We compare our framework with two other possible approaches: one is based on the observation that spatio-temporal objects correspond to three-dimensional spatial objects for which existing topological predicates can be exploited. The other approach is to consider possible transitions between spatial configurations. These considerations help to identify a canonical set of spatio-temporal predicates. Index Terms--Time in geographic information, spatio-temporal data types, representation of spatio-temporal objects, changes of spatial predicates, developments of spatial objects.

A prototypical network expert geographic information system (GIS) is developed to facilitate municipal solid waste landfill siting. A forward chaining knowledge base consisting of related siting rules extracted from various literature is used to establish an expert system. Siting analysis is performed by a GIS and evaluated by rules triggered from the expert system. The expert system and GIS are integrated into an expert GIS to combine the advantages of both systems. Also, a multimedia network interface is designed for local or remote access to the system from anywhere on the Internet. With the interface, a general user does not require previous knowledge of the expert system and GIS to use the system. This networking capability not only significantly reduces the cost of distributing tools to each user, but also avoids the difficulty that each user may encounter in installing and managing tools on the computer. Finally, a case study is provided to demonstrate the effectiveness of the developed system in facilitating landfill-siting analysis. The system can be directly accessed via Internet from the home page http://ev004.ev.nctu.edu.tw/ENGLISH/wsite/index.html.

We present an algorithm that estimates position using the Global Positioning System (GPS) C/A code measurements. We include an approximation for the covariance of the position estimate.

By relating the Global Positioning System (GPS) problem of location to the ancient Problem of Apollonius, this work presents a closed solution to the pseudorange positioning problem for two and three dimensions. The positioning problem, given by a set of nonlinear equations, has been reduced to the solution of a quadratic equation. The resulting expressions yield either two or one physically meaningful solutions for both the two- and three-dimensional problems. Expressions for the boundary curves and surfaces that separate the one-solution domain from the two-solution domains are also given. Asymptotic lines and planes for the boundary curves and surfaces have also been derived.

Carrier phase multipath is currently the limiting error source for high precision Global Positioning System (GPS) applications such as attitude determination and short baseline surveying. Multipath is the corruption of the direct GPS signal by one or more signals reflected from the local surroundings. Multipath reflections affect both the carrier phase measured by the receiver and signal-to-noise ratio (SNR). A technique is described which uses the SNR information to correct multipath errors in differential phase observations. The potential of the technique to reduce multipath to almost the level of receiver noise was demonstrated in simulations. The effectiveness on real data was demonstrated with controlled static experiments. Small errors remained, predominantly from high frequency multipath. The low frequency multipath was virtually eliminated. The remaining high frequency receiver noise can be easily removed by smoothing or Kalman filtering.