Construction of Geological Maps Using GIS -
A Case Study from Southern Lower Saxony, Germany

R. Seidemann³, S. Shumilov¹,
M. Breunig¹, A.B. Cremers¹, H.-J. Goetze², S. Schmidt², A. Siehl³

¹ Dept. of Computer Science III, University of Bonn, Germany
² FR Geophysik, FU Berlin, Germany
³ Dept. of Geology, University of Bonn, Germany

Abstract

The edition of geological maps by the aid of computers has increased enormously over the last years. However, up to now no software tools and no easy-to-handle solutions for the generation of geological maps from 3D-Geoinformation-Systems are available. The main target of the presented project is to fill this gap and to offer a basic approach. We propose a general solution to generate consistent geological maps from 3D-models. This requires interdisciplinary efforts from various parts of geoscience and computer science as well as differing software tools. Therefore, we are dealing with two main questions: (1) how to construct a consistent model and what kind of software tools should be used, and (2) how to get them work together.

Because any geological map is a projection of 3D-structures onto a 2D domain, the construction of a 3D-model is the basis for generating a map. Therefore, to achieve a consistent map, the underlying 3D-model has to be consistant. Maps generated in a traditional way may hide uncertainties, because the third dimension is not considered adequately in the construction process, due to the geometric complexity of the geological structures.

To avoid these shortcomings, we use geoscientific software for 3-D model generation and an object-oriented database to store geological data and structures. In addition, our approach combines geological and geophysical modeling software which leads to an accurate 3D-model fitting in the observed model constraints.

A first geological model of the studied area west of Hannover (Schaumburg-Lippe-Syncline and Weser-Monocline) is built on primary and derived data (e.g. analysis of field, drilling, seismic, and potential field data sets) using GoCad and Lynx for model construction. This model serves as basic information for both independent geometrical constraints and data input for the gravity modeling tool IGMAS (Interactive Gravity and Magnetic Application System). The resulting model is in turn used for further geological modeling. This process is repeated until a sufficient geological plausibility and accuracy of the model as well as an optimal fitting of modeled and measured gravity/magnetic field are obtained. The geological map will be generated by cutting the 3D-model with the DEM.

All data, geo-objects and models, that were generated during this process, are stored in GeoToolKit/GeoStore. This is a specialized object-oriented database built upon the top of the commercial ODBMS ObjectStore. Due to heterogeneity of used software tools and hardware platforms, the organisation of remote data access by native ObjectStore client-server communication facilities is not always possible. The main idea is to develop an open distributed environment that will integrate the remote geoscientific applications. Taking into account the object-oriented nature of data, the most suitable solution is Common Object Request Broker Architecture (CORBA). Using a standard middleware platform, we made our system extendible and accessible for all other CORBA-compilant applications.

Following appropriate standards for the integration of software components into a CORBA environment, we developed a wrapper around GeoToolKit/GeoStore database. Covering the ODBMS C++ Application Programming Interface (API) with an Interface Definition Language (IDL) interface, makes the database accessible to remote clients. By corresponding wrappers all other applications will be represented as isolated components accessible only through robustly defined IDL interfaces. The integration layer will be based on a global unified data model for spatial data which is compliant with the OGIS standard.

This work is funded by the German Research Foundation (DFG) as part of the program of the research group 'Interoperable Geoscientific Information System (IOGIS)', and the research grant Schm 844/4.
We acknowledge the receipt of industry data from various german oil companies which are active in the southern part of the Northwest German Basin.