DeKemp Eric Anthony. (2000). Threedimensional integration and visualization of structural field data : tools for regional subsurface mapping = Integration et visualisation 3D de données structurales de terrain : outils pour la cartographie géologique régionale. Thèse de doctorat, Université du Québec à Chicoutimi.

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Résumé
Threedimensional computer modelling of geological phenomena is rapidly emerging as a field within the already mushrooming science of computer visualization. In geological applications threedimensional interpretations are routinely performed through the use of twodimensional map data and knowledge about the geological history of an area. These interpretations are traditionally depicted with isometric or perspective block diagrams and vertical or horizontal crosssections. Constructing these threedimensional snapshots has been laborious, imprecise and limited to a single viewpoint. The methods presented here automate some of the more laborious tasks and enhance the threedimensional interpretation environment. Methodology focuses on using fieldbased structural data, from a variety of scales, to create speculative threedimensional surfaces that can be useful in addressing geological problems. These methods could help in resolving cryptic early fold geometry, extending stratiform mineralization and the subsurface interpretation of regional thrusts, unconformities or key lithostratigraphic boundaries. Several UNIX based programs are presented for performing the interpolation, extension and conversion tasks required in these approaches. Programs are implemented in conjunction with the commercial threedimensional visualization and modelling software EarthVision® and gOcad®. Algorithms focus on the densification and variable projection of distributed threedimensional data which share a common curvilinear geological feature. The result of the various interpolation and extension functions is the conversion of twodimensional lines to threedimensional surfaces.
A polynomial and hybrid BSpline interpolation technique optimizes geometric property components. The automated datadriven technique is applicable for geological problems in which structures are constrained by local linear and planar measurements. Input features are topographic intersections of relatively continuous irregular curved surfaces, which have a near linear known depth predictability at some point along the structure. The local direction cosine estimates derived along surface traces of geological structures are interpolated, and direction vectors linearly projected to depth to form local structural surfaces or 'ribbons'. The program is useful for depicting portions of variably plunging fold geometries as structural ribbons, which inturn act as visual guides during interpretive fold construction. Idealized and actual field examples of regionally continuous shear zones and brittle faults are presented, along with the development of threedimensional structural fabric trajectories, horizon propagation, and plutonic boundary geometry evaluation.
Semiautomated techniques are utilized with knowledgedriven interactive graphics. An interpretive or 'design' approach to surface construction is applied to low density data sets which are too sparse for standard global automated interpolation. Bézier curves and surface patches are implemented to act as interpretive construction lines that respect the constraints imposed by structural orientation data. The programs hinge.awk, cast.awk, bspline.awk and bezpatch.awk calculate the interpolated values from the spatial input data. Threedimensional construction lines are defined by tangents to local planar features, and the projection of key geologic structures. Supporting the interpolation tools, the program trace.awk estimates the local strike and dip of vertices along elevation registered threedimensional curvilinear map traces. The planar solution method can be applied in highrelief terrains, or to extend threedimensional curvilinear features from subsurface mining data.
Techniques are applied on field data from the lowrelief and structurally complex Archean Abitibi greenstone belt. Speculative models can be created from such terrains, provided data is respected and appropriate methods are applied at a given scale. The field component focuses on extracting data from maps and optimizing the threedimensional graphic editing environment for making better interpretations at outcrop, mine and regional scales.
Applied techniques used in this study include:
? Threedimensional structural symbology: the visualisation of threedimensional structural symbols representing point observations of bedding, lineations and foliation fabric;
? Structural attribution: the attachment of structural point observations to linear features through the use of a proximity filter. This is done with the program field.awk;
? Variable downplunge projection: the construction of custom downplunge projections from surface traces;
? Bézierbased graphics: examples of interactive threedimensional interpretations with Bézierbased curve;
? Hybrid surface design: a twostep approach to threedimensional geologic surface design using both Bézier patches and discrete smooth interpolation (DSI), constrained by map traces and local slopes;
? Threedimensional Map propagation: a method for propagating map elements using twodimensional map data and fieldbased plunge models. The program dive.awk is presented as an example of a simple propagation.
The results of this study indicate that a constrainedinterpretive approach to threedimensional visualization is valid for interpreting large to smallscale geological structures, even if the data base is limited to twodimensional mapbased information. This geometric approach provides an initial development path for what could become the routine combination of extracted geological map based information, surface topographic and structural data, and the intuitive knowledge of a geological 'designer'. The developed techniques listed above and presented in this study enhance the fieldbased geologists ability to create communicable threedimensional models of complex surfaces. Regardless of the state of visualization technologies, the success of threedimensional geological modelling is still dependent on the data density, clustering and depth variability of known structural observations. Most important perhaps are the geological relationships of local and regional structures with the bounding surfaces being modelled. New software will be needed to assess the quality of geological models based on these input parameters.
Type de document:  Thèse ou mémoire de l'UQAC (Thèse de doctorat) 

Date:  2000 
Lieu de publication:  Chicoutimi 
Programme d'étude:  Doctorat en ressources minérales 
Nombre de pages:  181 
ISBN:  1412308941 
Identifiant unique:  10.1522/12127333 
Département, module, service et unité de recherche:  Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre 
Directeur(s), Codirecteur(s) et responsable(s):  Mueller, Wulf Daigneault, Réal 
Motsclés:  Geological mapping, Cartographie géologique, 3D, ABITIBI, CAOPATINA, CARTOGRAPHIE, DONNEE, FORMATION, GEOLOGIE, GEOLOGIESTRUCTURALE, GEOLOGIQUE, GEOMATIQUE, MODELISATION, SNRC32G, STRUCTURAL, THESE 
Déposé le:  01 janv. 2000 12:34 

Dernière modification:  20 sept. 2011 15:33 
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