Catálogo de publicaciones - libros

Strokes are relatively simple linear elements readily perceived in a network. Apart from their role as graphical elements, strokes reflect lines of flow or movement within the network itself and so constitute natural functional units. Since the functional importance of a stroke is reflected in its perceived salience this makes strokes a suitable basis for network generalization, through the preferential preservation of salient strokes during data reduction. In this paper an exploration of the dual functional-graphical nature of strokes is approached via a look at perceptual grouping in generalization. The identification and use of strokes are then described. The strengths and limitations of stroke-based generalization are discussed; how the technique may be developed is also considered. Finally, the functional role of strokes in networks is highlighted by a look at recent developments in space syntax and related studies.

Virtual worlds, and especially the Internet, become increasingly important for advertisement, planning purposes, and simulation. Concepts that proved useful in the real world have been transferred to the Internet. A frequently seen example is the concept of navigation processes. In the real world such processes are based on the properties of space. A transfer to the virtual reality of the Internet is only useful if the properties of real space and virtual space are similar. In this paper we present different concepts of space and discuss their suitability for the Internet.

Spatial reasoning is a fundamental part of human cognition, playing an important role in structuring our activities and relationships with the physical world. A substantial body of spatial data is now available. In order to make effective use of this large quantity of data, the focus of GIS tools must shift towards helping a user derive relevant, high quality information from the data available. Standard GIS tools have lacked focus in this area, with querying capabilities being limited, and requiring a user to have specialized knowledge in areas such as set theory, or Structured Query Language (SQL). A fundamental issue in standard GIS is that, by relying entirely on numerical methods when working with spatial data, vagueness and imprecision can not be handled. Alternatively, qualitative methods for working with spatial data have been developed to address some key limitations in other standard numerical systems. TreeSap is a GIS application that applies qualitative reasoning, with a strong emphasis on providing a user with powerful and intuitive query support. TreeSap’s query interface is presented, along with visualization strategies that address the issue of conveying complex qualitative information to a user. The notion of a relative feature is introduced as an alternative approach to representing spatial information.

Current navigation services assume wayfinders new to an environment. In contrast, our focus is on route directions for wayfinders who are familiar with the environment, such as taxi drivers and couriers. We observe that people communicate route directions to these wayfinders in a hierarchical and granular manner, assuming some shared knowledge of the environment. These route directions do not focus on the route but rather on the destination. In this paper we solve the first problem of automatically generating route directions in a hierarchical and granular manner: finding the initial entity of such a communication. We propose a formal model to determine the initial entity, based on Grice’s conversational maxims, and applied to a topological hierarchy of elements of the city. An implementation of the model is tested for districts in a political subdivision hierarchy. The tests show a reasonable behavior for a local expert, and demonstrate the efficiency of granular route directions.

In this paper, we present an object-oriented approach to modeling mobile data and algorithms operating on such data. Our model is general enough to capture any kind of continuous motion while at the same time allowing for encompassing algorithms optimized for specific types of motion. Such motion may be available in a specific form, e.g., described by polynomials or splines, or implicitly restricted using bounds for speed or acceleration given by the application context.

Current Geographic Information Systems (GISs) adopt spatial database models that do not allow an easy interaction with users engaged in spatial analysis operations. In fact, users must be well aware of the representation of the spatial entities and specifically of the way in which the spatial reference is structured in order to query the database. The main reason of this inadequacy is that the current spatial database models violate the independence principle of spatial data. The consequence is that potentially simple queries are difficult to specify and strongly depends on the actual data in the spatial database.

In this contribution we tackle the problem of defining a database model to manage in a unified way (classes of spatial elements with common properties) with different levels of complexity. Complex spatial entities are defined by aggregation of primitive spatial entities; instances of spatial entities are called .

The database model is provided with an algebra to perform spatial queries over complex spatial entities; the algebra is defined in such a way it guarantees the independence principle and meets the closure property. By means of the operators provided by the algebra, it is possible to easily perform spatial queries working at the logical level only.

Many emerging applications of location-based services continuously monitor a set of moving objects and answer queries pertaining to their locations. Query processing in such services is critical to ensure high performance of the system. Observing that one predominant cost in query processing is the frequent accesses to the database, in this paper we describe how to reduce the number of moving object to database server round-trips by caching query information on the application server tier. We propose a novel-caching framework, named QACHE, which stores and organizes spatially-relevant queries for selected moving objects. QACHE leverages the spatial indices and other algorithms in the database server for organizing and refreshing relevant cache entries within a configurable area of interest, referred to as the cache-footprint, around a moving object. QACHE contains appropriate refresh policies and prefetching algorithms for efficient cache-based evaluation of queries on moving objects. In experiments comparing QACHE to other proposed mechanisms, QACHE achieves a significant reduction (from 63% to $99%) in database roundtrips thereby improving the throughput of an LBS system.

Although the map algebra framework is very popular within the GIS community for modelling fields, the fact that it is solely based on raster structures has been severely criticised. Instead of representing fields with a regular tessellation, we propose in this paper using the Voronoi diagram (VD), and argue that it has many advantages over other tessellations. We also present a variant of map algebra where all the operations are performed directly on VDs. Our solution is valid in two and three dimensions, and permits us to circumvent the gridding and resampling processes that must be performed with map algebra.

Most object-based approaches to Geographical Information Systems (GIS) have concentrated on the representation of geometric properties of objects in terms of fixed geometry. In our road traffic marking application domain we have a requirement to represent the static locations of the road markings but also enforce the associated regulations, which are typically geometric in nature. For example a give way line of a pedestrian crossing in the UK must be within 1100–3000 mm of the edge of the crossing pattern. In previous studies of the application of spatial rules (often called ‘business logic’) in GIS emphasis has been placed on the representation of topological constraints and data integrity checks. There is very little GIS literature that describes models for geometric rules, although there are some examples in the Computer Aided Design (CAD) literature. This paper introduces some of the ideas from so called variational CAD models to the GIS application domain, and extends these using a Geography Markup Language (GML) based representation. In our application we have an additional requirement; the geometric rules are often changed and vary from country to country so should be represented in a flexible manner. In this paper we describe an elegant solution to the representation of geometric rules, such as requiring lines to be offset from other objects. The method uses a feature-property model embraced in GML 3.1 and extends the possible relationships in feature collections to permit the application of parameterized geometric constraints to sub features. We show the parametric rule model we have developed and discuss the advantage of using simple parametric expressions in the rule base. We discuss the possibilities and limitations of our approach and relate our data model to GML 3.1.

Efficiently exploring a large spatial dataset with the aim of forming a hypothesis is one of the main challenges for information science. This study presents a method for exploring spatial data with a combination of spatial and visual data mining. Spatial relationships are modeled during a data pre-processing step, consisting of the density analysis and vertical view approach, after which an exploration with visual data mining follows. The method has been tried on emergency response data about fire and rescue incidents in Helsinki.