Eric Guilbert

Multi-level representation of terrain features on a contour map

Contour lines are important for quantitatively displaying relief and identifying morphometric features on a map. Contour trees are often used to represent spatial relationships between contours and assist the user in analysing the terrain. However, automatic analysis from the contour tree is still limited as features identified on a map by sets of contours are not only characterised by local relationships between contours but also by relationships with other features at different levels of representation. In this paper, a new method based on adjacency and inclusion relationships between regions defined by sets of contours is presented. The method extracts terrain features and stores them in a feature tree providing a description of the landscape at multiple levels of detail. The method is applied to terrain analysis and generalisation of a contour map by selecting the most relevant features according to the purpose of the map. Experimental results are presented and discussed.

A multi-agent system approach for feature-driven generalization of isobathymetric line

Generalization is an important branch in cartography. This process abstracts a map for emphasizing important items and increasing its legibility. On a nautical chart, the purpose is also to emphasize navigational hazards and main navigation routes. Therefore, the cartographer not only adapts the amount of information to the scale of the chart but also selects the information according to the types of features on the seabed and their impor- tance to the navigator. Features are characterized by the isobaths. Methods usually applied on contours for topographic maps cannot be applied on isobaths as they do not take information about features into consideration and a new strategy coordinating different generalization operators must be defined for nautical charts. This paper focuses on isobaths generalization and introduces a new approach based on a multi-agent system. It first in- troduces the characteristics and constraints of isobath generalization. Then it presents the multi agent model where features and isobaths are repre- sented by agents at different levels. Possible actions performed by each agent are presented with measures for evaluating their results according to generalization constraints.

Object-oriented tracking of the dynamic behavior of urban heat islands

ABSTRACT The urban heat island (UHI) phenomenon occurring within urban areas or city-clusters is increasingly becoming a severe problem in the urbanization process. Previous research mainly focusing on static UHI modeled at fixed time instants is not capable to track the evolutionary process of the UHIs in both time and space domains. This research designs an object-oriented dynamic model to reconstruct the evolutionary process of UHIs. Each UHI is modeled as a spatiotemporal field-object with its own life-cycle. The dynamic behavior of an UHI is defined by a series of filiations (e.g. expansion and contraction). The model was implemented in an object-relational database and applied to air temperature data collected from weather stations in hourly basis over 7 days. The behaviors of UHI were extracted from the data. Results suggest that the model can effectively identify different behaviors and status of UHIs, and reveal the spatiotemporal behavior of each of them.

An Ontology of the Submarine Relief for Analysis and Representation on Nautical Charts

Abstract A nautical chart is a kind of map used to describe the seafloor morphology and shoreline of adjacent lands. One of its main purposes is to guarantee safety of navigation. As a consequence, the construction of a nautical chart follows very specific rules. The cartographer has to select and highlight undersea features according to their relevance to navigation. In an automated process, the system must be able to identify and classify these features from the terrain model. This paper aims therefore to define ontologies of the submarine relief and nautical chart that will be at the root of a model-oriented generalization process. To the best of our knowledge, no ontology has been defined to formalize the geographical and cartographic objects for nautical chart representation. Thus, a bottom-up approach was developed to extract and model knowledge derived from standards established by the International Hydrographic Organization (IHO) and cartographers’ expertise. The submarine relief ontology formalizes undersea features describing the submarine relief. Four concepts (composition, morphometric class, shape value and depth value) are introduced to describe properties and relationships between undersea features. The cartographic representation ontology of nautical charts will define several concepts (chart, features, isobathymetric lines and soundings) for the representation of undersea features on the chart.

Automatic drainage pattern recognition in river networks

In both geographic information system and terrain analysis, drainage systems are important components. Owing to local topography and subsurface geology, a drainage system achieves a particular drainage pattern based on the form and texture of its network of stream channels and tributaries. Although research has been done on the description of drainage patterns in geography and hydrology, automatic drainage pattern recognition in river networks is not well developed. This article introduces a new method for automatic classification of drainage systems in different patterns. The method applies to river networks, and the terrain model is not required in the process. A series of geometric indicators describing each pattern are introduced. Network classification is based on fuzzy set theory. For each pattern, the level of membership of the network is given by the different indicator values. The method was implemented, and the experimental results are presented and discussed.

Conflict Removal between B-spline Curves for Isobathymetric Line Generalization using a Snake Model

This paper describes a method for suppressing distance conflicts between isobathymetric lines modeled with B-spline curves for cartographic generalization. The initial B-spline curves are obtained by compressing a set of polygonal lines representing the raw data. The conflict removal is realized by respecting strong cartographic constraints, such as the navigation safety and the legibility of the map, and weak constraints, such as the preservation of the submarine relief. A polygonal line representing the minimal displacement that corrects a conflict is first computed. Then, the curve is deformed using a snake model. The constraints are expressed via different energy terms, and the curve is deformed until a valid solution is reached. In order to apply the method without user intervention, the shape parameters of the snake are set automatically. The advantage of the method is that it ensures the respect of strong constraints in every case while taking into account the weaker ones. The method can also be applied to the correction of visual self-intersections. The use of a snake model combined with B-spline curves permits a better control of the deformation than polygonal lines, better preserving of the shape of the curves. Examples of real case studies issued from bathymetric databases are provided, and the benefits and drawbacks of the method are discussed.

Feature‐driven generalization of isobaths on nautical charts: a multi‐agent system approach

A nautical chart provides a schematic view of the seafloor where isobaths (contour lines joining points of same depth) and depth soundings are generalized to highlight undersea features that form navigational hazards and routes. Considering that the process is ultimately driven by features and their significance to navigation, this article proposes a generalization strategy where isobath generalization is controlled by undersea features directly. The seafloor is not perceived as a continuous depth field but as a set of discrete features composed by groups of isobaths. In this article, generalization constraints and operators are defined at feature level and composed of constraints and operators applying to isobaths. In order to automate the process, a multi-agent system is designed where features are autonomous agents evaluating their environment in order to trigger operations. Interactions between agents are described and an example on a bathymetric database excerpt illustrates the feasibility of the approach.

An Ontology for Submarine Feature Representation on Charts

A landform is a subjective individuation of a part of a terrain. Landform recognition is a difficult task because its definition usually relies on a qualitative and fuzzy description. Achieving automatic recognition of landforms requires a formal definition of the landforms properties and their modelling. In the maritime domain, the International Hydrographic Organisation published a standard terminology of undersea feature names which formalises a set of definition mainly for naming and communication purpose. This terminology is here used as a starting point for the definition of an ontology of undersea features and their automatic classification from a terrain model. First, an ontology of undersea features is built. The ontology is composed of an application domain ontology describing the main properties and relationships between features and a representation ontology deals with representation on a chart where features are portrayed by soundings and isobaths. A database model was generated from the ontology. Geometrical properties describing the feature shape are computed from soundings and isobaths and are used for feature classification. An example of automatic classification on a nautical chart is presented and results and on-going research are discussed.

Line Decomposition Based on Critical Points Detection

The problem of line simplification is a recurrent problem in cartography. The purpose is to remove irrelevant details while emphasising the main features of the line. Most of the current techniques belong to the spatial domain (least square method, active contour, point selection). However, some techniques applying to the frequency domain (Fourier transform, wavelets) have also been introduced. These latter methods are mostly employed for simplification and compression purposes where information about line features is rarely taken into account, thus limiting their usefulness for cartographic applications. This paper presents the principle of Empirical Mode Decomposition which belongs to the frequency domain. It is used in signal processing to decompose a signal into its different frequencies. The method for line simplification has been studied, showing that line features can be taken into account by introducing a new decomposition method based on the detection of critical points. Results obtained at different levels of detail are discussed. Finally, future directions for work are presented.

An ontology-driven multi-agent system for nautical chart generalization

ABSTRACT On nautical charts, undersea features are portrayed by sets of soundings (depth points) and isobaths (depth contours) from which map readers can interpret undersea features. Different techniques were developed for automatic sounding selection and isobath generalization. These methods are mainly used to generate a new chart from the bathymetric database or from a larger scale chart through selection and simplification. However, a part of the process consists in selecting and emphasizing undersea features formed by groups of soundings and isobaths on the chart according to their relevance to maritime navigation. Hence, automation of the process requires classification of features and their generalization through the application of a set of operators according not only to geometric constraints but also to their meaning. The objective of this work is to conceive a multi-agent system (MAS) for nautical chart generalization that is driven by the knowledge on the generalization process and the undersea features and their relationships. First, this work provides a feature-centered ontology modeling of the generalization process. Then, the MAS structure is introduced where agents access cartographic knowledge stored in the ontology. The MAS makes use of measure algorithms to evaluate constraint violations on the chart in order to decide which generalization operators to apply. The whole model has been implemented to provide generalization plans on a real case study.