Three-dimensional integration and visualization of structural field data: Tools for regional subsurface mapping

Three-dimensional computer modelling of geological phenomena is rapidly emerging as a field within the already mushrooming science of computer visualization. In geological applications three-dimensional interpretations are routinely performed through the use of two-dimensional 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 cross-sections. Constructing these three-dimensional snap-shots has been laborious, imprecise and limited to a single viewpoint. The methods presented here automate some of the more laborious tasks and enhance the three-dimensional interpretation environment. 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 three-dimensional visualization and modelling software EarthVision® and gOcad ®.; A polynomial and hybrid B-Spline interpolation technique optimizes geometric property components. The automated data-driven 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 in-turn 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 three-dimensional structural fabric trajectories, horizon propagation, and plutonic boundary geometry evaluation.; Semi-automated techniques are utilized with knowledge-driven 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. Three-dimensional 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 three-dimensional curvilinear map traces. The planar solution method can be applied in high-relief terrains, or to extend three-dimensional curvilinear features from sub-surface mining data. (Abstract shortened by UMI.)...