Thomas Devogele

On spatial database integration

This paper investigates the problems that arise when application requirements dictate that autonomous spatial databases be integrated into a federated one. The paper focuses on the most critical issues raised by the integration of databases of different scales. A short presentation of approaches to interoperability and of the main steps composing the integration process is given first. Next, a general format is proposed for precisely defining correspondences between objects of two databases. The format can deal with a wide range of discrepancies in GIS data. Last, a solution is presented for aggregation conflicts which arise when one object of one database corresponds to a set of objects in the other database, a very frequent case when the databases are of different scales. The method is applied to excerpts of real cartographic databases.

Matching Networks with Different Levels of Detail

This paper deals with the issue of automatically matching networks with different levels of details. We first present why this issue is complex through an analysis of the differences that can be encountered between networks. We also present different criteria, tools and approaches used for network matching. We then propose a matching process, named NetMatcher. This process is a several steps process looking for potential candidates and then analysing them in order to determine the final results. It relies on the comparison of geometrical, attributive, and topological properties of objects. It determines one-to-many links between networks: in particular a node of the less detailed network can be matched to several arcs and nodes forming a complex junction in the most detailed network. An important strength of the process is to self-evaluate its results through the comparison of topological organisation of networks. This paves the way to an interactive editing of the results. The NetMatcher process has been intensively tested on a wide range of actual datasets, thus highlighting its effectiveness as well as its limits.

A New Merging Process for Data Integration Based on the Discrete Fréchet Distance

The overlay process is currently one of the main computational solutions used to integrate several data layers from different sources. Unfortunately, it is problematic when trying to overlay many layers. This leads to several geometric problems such as the management of sliver polygons. This paper proposes a new merging process to complement the vector overlay for data integration of several layers. This process, based on measures derived from the Frechet distance, matches common points (either lines or polygons). It also merges an ordered set of pairs of matching points (vertices) into a single geometry.

A Relative Representation of Trajectories in Geogaphical Spaces

The research presented in this paper introduces a relative representation of trajectories in space and time. The objective is to represent space the way it is perceived by a moving observer acting in the environment, and to provide a complementary view to the usual absolute vision of space. Trajectories are characterized from the perception of a moving observer where relative positions and relative velocities are the basic primitives. This allows for a formal identification of elementary trajectory configurations, and their relationships with the regions that compose the environment. The properties of the model are studied, including transitions and composition tables. These properties characterize trajectory transitions by the underlying processes that semantically qualify them. The approach provides a representation that might help the understanding of trajectory patterns in space and time.

Coastline Matching Process Based on the Discrete Fréchet Distance

Spatial distances are the main tools used for data matching and control quality. This paper describes new measures adapted to sinuous lines to compute the maximal and average discrepancy: Discrete Frechet distance and Discrete Average Frechet distance. Afterwards, a global process is defined to automatically handle two sets of lines. The usefulness of these distances is tested, with a comparison of coastlines. The validation is done with the computation of three sets of coastlines, obtained respectively from SPOT 5 orthophotographs and GPS points. Finally, an extension to Digital Elevation Model is presented.

Maritime GIS: From Monitoring to Simulation Systems

Combined research in the fields of Geographical Information Systems (GIS) and maritime systems has finally reached the point where paths should overlap and continue in better unison. This paper introduces methodological and experimental results of several marine-related GIS projects whose objectives are to develop spatial data models and computing architectures that favour the development of monitoring and decision-aid systems. The computing architectures developed integrate agent-based reasoning and distributed systems for the real-time monitoring, manipulation and simulation of maritime transportation systems.

A formal model for representing point trajectories in two-dimensional spaces

Modelling moving points is a subject of interest that has attracted a wide range of spatio-temporal database research. Efforts so far have been oriented towards the development of database structures and query languages. The preliminary research presented in this paper introduces a formal analysis of spatio-temporal trajectories, where the objective is to complement current proposals by a categorization of the underlying processes that characterize moving points. The model introduced identifies the semantic exhibited by point versus point, point versus line and point versus region trajectories.

Web architecture for monitoring and visualizing mobile objects in maritime contexts

Recent advances in telecommunication and positioning systems, web and wireless architectures offer new perspectives and challenges to the management and visualization of mobile and geo-referenced objects. Amongst many research challenges still opened, the development of integrated sensorbased architectures necessary to the integration of mobile data has been often neglected. Real-time integration of sensor-based data, their management within a distributed system, and diffusion to different levels of services and interfaces to what should be considered as a collaborative web GIS constitutes the objective of the research presented in this paper. This paper introduces a modular and experimental web GIS framework applied to maritime navigation, and where mobile objects behave in a maritime environment. Different levels of services are developed, including a web-based wireless access and interface to a traffic monitoring application.

Trajectory Box Plot: a new pattern to summarize movements

Nowadays, an abundance of sensors are used to collect very large datasets of moving objects. The movement of these objects can be analysed by identifying common routes. For this, a cluster of trajectories must be defined and the pattern of each cluster discovered. In this article, we introduce a new pattern, called the Trajectory Box Plot (TBP), to summarize a set of trajectories following the same route. The TBP is an extension of the well-known descriptive statistics Box Plot concept. Each TBP is described by a median trajectory, a 3D box and a 3D fence. The median trajectory depicts the typical movement of mobile objects. The box and the fences (whiskers) describe the spatial and temporal spreading around the central tendency. TBPs are useful to summarize and analyse trajectory streams, understand their spatio-temporal density and detect outliers. In this article, visual analysis highlights how the TBP pattern effectively describes how the density of trajectory clusters change over time.

Towards distributed convoy pattern mining

Mining movement data to reveal interesting behavioral patterns has gained attention in recent years. One such pattern is the convoy pattern which consists of at least m objects moving together for at least k consecutive time instants where m and k are user-defined parameters. Existing algorithms for detecting convoy patterns, however do not scale to real-life dataset sizes. Therefore a distributed algorithm for convoy mining is inevitable. In this paper, we discuss the problem of convoy mining and analyze different data partitioning strategies to pave the way for a generic distributed convoy pattern mining algorithm.