GIS Data Modelling

Abstract: This paper describes a unified framework for the problems of modelling and processing spatial entities. We propose a general definition of spatial objects, and show that the different types of spatial data can be expressed as particular cases of this definition. Furthermore, we present a taxonomy for the various types of GIS operations, defined in terms of the properties of this definition. Our goal is to argue that GIS data types and operations can be defined based on a single formal notion, which encapsulates the GIS concepts of both continuous fields and discrete features, with important consequences for system and interface design, interoperabilty issues and language proposal.

Resumo: Este artigo define objetos geográficos, que servem como base formal para a definição dos outros tipos de dados geográficos, englobando tanto geo-campos quanto geo-objetos. Este artigo não aborda implementação e sim a modelagem matemática destes objetos geográficos. São propostas quatro classificações possíveis de objetos geográficos: simples e homogênea, composta e homogênea, simples e não homogênea e composta e não-homogênea. São definidas operações sobre objetos geográficos, que podem ser atômicas ou compostas. A idéia é que operações complexas possam ser definidas a partir de operações atômicas. O artigo cita algumas operações, como: Alteração/Consulta de atributos, Relacionamento Espacial, Distância, etc.

Abstract: Geographic representation has become more complex through time as researchers have added new concepts, leading to apparently endless proliferation and creating a need for simplification. We show that many of these concepts can be derived from a single foundation that we term the atomic form of geographic information. The familiar concepts of continuous fields and discrete objects can be derived under suitable rules applied to the properties and values of the atomic form. Fields and objects are further integrated through the concept of phase space, and in the form of field objects. A second atomic concept is introduced, termed the geo-dipole, and shown to provide a foundation for object fields, metamaps, and the association classes of object-oriented data modelling. Geographic dynamics are synthesized in a three-dimensional space defined by static or dynamic object shape, the possibility of movement, and the possibility of dynamic internal structure. The atomic form also provides a tentative argument that discrete objects and continuous fields are the only possible bases for geographic representation.

Resumo: Com o foco voltado mais para a teoria que para a prática, este artigo propõe um framework conceitual e prático para esclarecer e integrar pensamentos sobre representações geográficos em SIG. Propõe o geo-átomo como sendo uma abstração a partir do qual outros elementos geográficos poderão ser derivados.

Abstract: Geospatial data modelling is dominated by the distinction between continuousfield and discrete-object conceptualizations. However, the boundary between them is not always clear, and the field view is more fundamental in some respects than the object view. By viewing a set of objects as an object field and unifying it with conventional field models, a new concept, the General Field (G-Field) model, is proposed. In this paper, the properties of G-Field models, including domain, range, and categorization, are discussed. As a summary, a descriptive framework for G-Field models is proposed. Then, some common geospatial operations in geographic information systems are reconsidered from the G-Field perspective. The geospatial operations are classified into order-increasing operations and non-order-increasing operations, depending on changes induced in the G-Field’s order. Generally, the order can be viewed as an indicator of the level of information extraction of geospatial data. It is thus possible to integrate the concept of order with a geo-workflow management system to support geographic semantics.

Resumo: A partir da unificação dos conceitos de geo-campos e geo-objetos, o artigo propõe um novo conceito: General Field (G-Field) . Um framework para os modelos G-Field também é proposto, sendo que enfoca também conceitos de implementação. Goodchild argumenta que todas as informações geográficas podem ser decompostas em conjuntos de pontos ou geo-átomos.

Abstract: Earth sciences are about to follow the mapping domain where raster data increasingly get integrated in online services, contribute by far the largest volume. Interestingly, although more and more raster services are getting online, there is few work on a comprehensive model of raster services, rather architectures are of ad-hoc style and optimized towards very narrow applications, such as fast zoom and pan on seamless maps. We claim that databases introduce a new quality of service on high-volume multi-dimensional earth science raster data, characterized by clear and understandable concepts, extensibility, and scalability. To support this, we present a comprehensive conceptual model for raster data in earth science and discuss how an efficient architecture can be derived from it, which is implemented in the rasdaman system. Further, we show how such concepts play a role in the development of OGC's geo raster services, WCS and WCPS. Finally, we discuss some research challenges.

Resumo: Propõe um modelo conceitual para dados Raster. Discute como uma arquitetura eficiente pode ser derivada a partir deste modelo. Implementado no sistema Rasdaman, o modelo possui algumas características importantes:

• Baseado em arrays n-dimensionais, podendo ter qualquer dimensão, qualquer extensão e qualquer tipo de célula;
• Permite particionamento em blocos, não necessariamente regulares. Usa índices geo para rapidamente determinar os blocos consultados;
• Opcionalmente, blocos e também resultados de consultas podem ser comprimidos;
• Oferece paralelismo entre consultas e estudos pretendem aplicar o paralelismo dentro de uma mesma consulta.

Propõe também uma extensão do modelo WCS (Web Coverage Service), permitindo análise e navegação não-trivial em Rasters de larga-escala, bem como outras melhorias.