From 3d geomodelling systems towards 3d geoscience information systems: Data model, query functionality, and data management

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Abstract

Two-dimensional GIS are extensively used in geology to create, analyse, and interpret geological map models. However, these systems are unable to represent the Earth's subsurface in three spatial dimensions. The objective of this article is to overcome this deficiency and to provide a general framework for a 3d GIS.

The presented approach is based on existing 3d geomodelling theory and software, and is characterized by an integrated data model for geological observation data and geomodels, data management supported by an XML-enabled database server, and functionality for querying observation data and 3d geomodels based on their 3d spatial and geological properties. The resulting 3d GIS framework enables geologists to manipulate, analyse and interpret 3d geomodels analogously as they work with 2d geological maps.

Introduction

Geoscience Information Systems (GIS) provide a means to create and analyse models of real world geological situations based on data. In contemporary two-dimensional (2d) GIS, geological objects are represented as map objects in two spatial dimensions. These systems are not appropriate for three-dimensional (3d) geological applications as they are not capable of representing 3d spatial geological relationships and properties with 3d spatial variation. Two-dimensional GIS and so-called 2.5-dimensional GIS represent the altitude values z of geoobjects as a continuous function of the geographical coordinates: z=f(x,y). Such systems cannot model 3d geological objects whose boundary geometry features multiple z-values for a single x,y-value, like thrusts and faulted horizons.

On the other hand, 3d geomodelling software provides data models and functionality to represent sophisticated geological situations in three spatial dimensions as geomodels. Geomodelling systems are widely applied in the petroleum and mining exploration industry, geological surveys, and academic science departments. Such systems are commonly based on 3d discrete topological data models and special interpolation methods like, Discrete Smooth Interpolation (Mallet, 2002) and structural inversion (Courrioux et al., 2001). In a sense, 3d geomodelling software can be regarded as a fundamental 3d GIS user application.

The increase of digital geodata and the possibility to create detailed regional geological 3d geomodels (see, for example, Fig. 1) results in new, specific needs for geodata management, and new opportunities for geodata query and analysis. However, these fields are underdeveloped in existing 3d geomodelling environments. This becomes obvious when comparing geomodelling software with mature 2d geographical information systems. For example, queries like “Select all structural observation points with azimuth=12±10,dip=24±15 and distance from a given fault d<1km” are not intrinsic features of geomodelling systems.

The objective of this work has been the development of geologically sensible query functionality for spatial and non-spatial properties of geoobjects, and the integration of 3d geological modelling and data management system components in a generic framework. The underlying data management should provide maximum interoperability, flexibility, and long-term usability.

Section snippets

Adapting 3d data models for 3d GIS

An integrated data model for geological data needs to account for both primary observed data and geomodels. The work presented here follows the geomodelling concepts of Mallet (Mallet, 2002). A geomodel is an abstract digital representation of a part of the Earth's subsurface. Geomodels are derived by interpolation and interpretation of data observed at points and can represent geological situations in 3d space. Knowledge and geophysical models may, for example, be used as additional

Requirements

An essential functionality of GIS is the capability to select and investigate geodata by the means of query. While the aspects of spatial geoscience queries have been extensively studied in the context of 2d GIS (for example, Bonham-Carter, 1994), few workers examined 3d spatial geoscience queries in GIS, namely Breunig (1996). This may be due to the relatively late advent of 3d geomodelling systems which allow to build sophisticated geomodels. The investigation of 3d geomodels of large and

Geodata management and implementation features

For common 3d geomodelling projects a large amount of geodata need to be stored and served to many users for a long time. Therefore, for 3d GIS projects it is essential to have an efficient and reliable data management. Currently, no appropriate solution for the integrated, XML-based storage and query of primary geological data and 3d geomodels exists. Therefore a data management system is suggested which features

  • (1)

    A client-server architecture, where geomodelling applications act as clients of a

Conclusions and results

While geomodelling software is increasingly used by geologists in academic research, geological surveys and industry, such software is not intrinsically equivalent to a 3d GIS. Instead, it can be considered the core component of a 3d GIS which provides sophisticated spatial modelling functionality. Extending the data model with geological semantics opens the door for complex spatial and non-spatial queries and thus 3d GIS environments, analogously to 2d GIS used for the creation and

Acknowledgement

The author acknowledges Dr. E. de Kemp (NRCan, Ottawa) for his remarks on the manuscript.

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