Miguel Rodríguez Luaces

Measuring consistency with respect to topological dependency constraints

In contrast to the enormous development of database management systems to support spatial databases, very little work has been done in evaluating the quality of spatial data in terms of how much they satisfy a set of topo-semantic integrity constraints, in particular, a set of topological dependency constraints. In the same way, mechanisms for enforcing the satisfaction of those constraints are not necessarily available or even feasible. In this paper we propose measures to evaluate the degree of violation of a topological dependency constraint by geometries stored in a spatial database instance. We also propose how these measures can be aggregated to globally evaluate the data quality of a database instance such that they enable to compare database instances in terms of their constraint satisfaction. We provide an experimental evaluation of those measures using synthetic and real data. We validate our measures by i) analyzing their correlation with the semantic distance of topological relations and ii) checking that the more we randomly modify geometries to make database instances inconsistent, the more our global data quality measure decreases, showing its sensibility to the introduced constraint violations.

A fun application of compact data structures to indexing geographic data

The way memory hierarchy has evolved in recent decades has opened new challenges in the development of indexing structures in general and spatial access methods in particular. In this paper we propose an original approach to represent geographic data based on compact data structures used in other fields such as text or image compression. A wavelet tree-based structure allows us to represent minimum bounding rectangles solving geographic range queries in logarithmic time. A comparison with classical spatial indexes, such as the R-tree, shows that our structure can be considered as a fun, yet seriously competitive, alternative to these classical approaches.

The Galician virtual library

Purpose – This study aims to present the digital library Galician virtual library (BVG, for “Biblioteca Virtual Galega”) in Galician.Design/methodology/approach – The paper shows the objectives pursued by the BVG, its development, putting special emphasis on the main technological challenges, and presents some data about its usage.Findings – A digital library can be used to stimulate a lesser‐used language and to promote the culture and tourism of a region.Originality/value – The paper shows how a digital library can be used to strengthen the Galician language, which is currently categorised as a “Lesser Used Language” in the European Community and to contribute to the preservation and spreading of Galician culture and literary works, either from current authors or from previous documents. It also provides a digital publishing house for new authors and opens a communication channel between current authors and their readers. Finally, it helps to connect a scattered community like the Galician, offering a c...

A New Point Access Method Based on Wavelet Trees

The development of index structures that allow efficient retrieval of spatial objects has been a topic of interest in the last decades. Most of these structures have been designed for secondary memory. However, in the last years the price of memory has decreased drastically. Nowadays it is feasible to place complete spatial indexes in main memory. In this paper we focus in a subcategory of spatial indexes named Point Access Methods. These indexes are designed to solve the problem of indexing points. We present a new index structure designed for two dimensions and main memory that keeps a good trade-off between the space needed to store the index and its search efficiency. Our structure is based on a wavelet tree , which was originally designed to represent sequences, but has been successfully used as an index in areas like information retrieval or image compression.

A generic framework for GIS applications

Geographic information systems (GIS) are becoming more usual due to the improved performance of computer systems. GIS applications are being developed using the three-tier software architecture traditionally used for general-purpose information systems. Even though this architecture is suitable for GIS applications, the special nature and exclusive characteristics of geographic information pose special functional requirements on the architecture in terms of conceptual and logical models, data structures, access methods, analysis techniques, or visualization procedures. In this paper, we propose a generic architecture for GIS that provides support for the special nature of geographic information and conforms with the specifications proposed by the ISO/TC 211 and the OGC. Our strategy to achieve this goal consists of two steps: (i) we analyze the special characteristics of GIS with respect to traditional information systems, (ii) and we adapt the traditional three-tier architecture for information systems to take into account the special characteristics of GIS. Finally, we have tried to apply the architecture that we propose in the development of a complete and complex real-life GIS application using commercial tools in the analysis, design and implementation. We describe this application, and we use it to describe the limitations of current commercial GIS development tools by analyzing the differences in the architecture of the resulting system with respect to our proposal.

Space-efficient representations of rectangle datasets supporting orthogonal range querying

The increasing use of geographic search engines manifests the interest of Internet users in geo-located resources and, in general, in geographic information. This has emphasized the importance of the development of efficient indexes over large geographic databases. The most common simplification of geographic objects used for indexing purposes is a two-dimensional rectangle. Furthermore, one of the primitive operations that must be supported by every geographic index structure is the orthogonal range query, which retrieves all the geographic objects that have at least one point in common with a rectangular query region. In this work, we study several space-efficient representations of rectangle datasets that can be used in the development of geographic indexes supporting orthogonal range queries.

An Ontology-Based Index to Retrieve Documents with Geographic Information

Both Geographic Information Systemsand Information Retrievalhave been very active research fields in the last decades. Lately, a new research field called Geographic Information Retrievalhas appeared from the intersection of these two fields. The main goal of this field is to define index structures and techniques to efficiently store and retrieve documents using both the text and the geographic references contained within the text. We present in this paper a new index structure that combines an inverted index, a spatial index, and an ontology-based structure. This structure improves the query capabilities of other proposals. In addition, we describe the architecture of a system for geographic information retrieval that uses this new index structure. This architecture defines a workflow for the extraction of the geographic references in the document.

An inconsistency measure of spatial data sets with respect to topological constraints

An inconsistency measure can be used to compare the quality of different data sets and to quantify the cost of data cleaning. In traditional relational databases, inconsistency is defined in terms of constraints that use comparison operators between attributes. Inconsistency measures for traditional databases cannot be applied to spatial data sets because spatial objects are complex and the constraints are typically defined using spatial relations. This paper proposes an inconsistency measure to evaluate how dirty a spatial data set is with respect to a set of integrity constraints that define the topological relations that should hold between objects in the data set. The paper starts by reviewing different approaches to quantify the degree of inconsistency and showing that they are not suitable for the problem. Then, the inconsistency measure of a data set is defined in terms of the degree in which each spatial object in the data set violates topological constraints, and the possible representations of spatial objects are points, curves, and surfaces. Finally, an experimental evaluation demonstrates the applicability of the proposed inconsistency measure and compares it with previously existing approaches.

Improving Accessibility of Web-Based GIS Applications

A major problem of vector active map formats such as WebCGM and scalable vector graphics (SVG) is that, in order to display them in most Web browsers, either a plug-in has to be installed or an applet has to be downloaded. In this paper, a Web service is presented whose functionality enables the transformation of vector active maps from SVG to a new DHTML (HTML+JavaScript) active map representation, improving this way the accessibility of Web-based GIS applications. This new representation, which is also part of the present work, includes a raster representation of the map and a vector representation of its geographic objects. The former is used as a background image of the map whereas the latter enables the response to user-triggered events. An R-tree spatial index structure is used to access the geographic objects affected by each event in order to execute the relevant action

Using geographical information systems to browse touristic information.

The current expansion of Internet makes it one of the most popular places to publish and search for almost any kind of information. In particular, touristic information, not only about tours or information about resources, places, museums or monuments, but also cultural tourism, has gained much attention in the last years. We propose the use of geographical information systems technology (GIS) that provides interfaces capable of displaying interactive maps with information associated to the elements present in such maps. In this paper, we present a Web interface to access touristic information about Galicia (Spain) using GIS technology to easily find any touristic or cultural information. This interface is enclosed in the Galician Virtual Library (http://bvg.udc.es) Web site.