Interactive Editing of Sealed Geological 3D Models

1. Abstract We propose a method to interactively modify contacts between surfaces in a 3D boundaryrepresentation geological model. The modification is based on a hierarchy between a slip surface (a surface that other surfaces can slide along, which in geology could include faults, erosion surfaces, salt tops) and a secondary, deformable surface (e.g. horizon, older fault). The border of the deformable surface is allowed to move along the slip surface, and the deformation mechanism watches for and prevents the creation of new spatial regions. The method only uses a mouse as input device; the interaction consists of three main steps: selection of a point on the contact, displacement of the mouse cursor, and release of the point at the new position. During selection, the boundary elements inside a user-defined area of influence are detected and classified. The slip surface in then parameterized locally to allow the mapping of that surface to a plane. During manipulation, a proper position of the input point in 3D space is ensured with a snap-dragging approach. The border of the deformed surface is then interpolated in the parametric space of the slip surface. This deformation can be propagated locally to the reshaped surface, taking care that no collision occurs with other region boundaries. At the end of the manipulation, the split surface is re-triangulated locally in order to maintain the model consistency. This triangulation is performed in 2D parametric space with a constrained Delaunay approach. As new intersections may appear between the reshaped contact and others contacts on the slip surface, some edges used as Delaunay constraints need to be split before the triangulation. The last step is a local updating of the 3D model regions definitions, as the topology of the slip surface may have changed during the modification.