PySubdiv: open-source geological modelling and reconstruction by non-manifold subdivision surfaces

Abstract. Sealed geological models are commonly used as an input to process simulations, for example in hydrogeological or geomechanical studies. Creating these meshes often requires tedious manual work – and it is, therefore, difficult to adjust a once-created model. In this work, we propose a flexible framework to create and interact with geological models using explicit surface representations. The essence of the work lies in the determination of the control mesh and the definition of semi-sharp creases values which, in combination, enable the representation of complex structural settings with a low number of control points. We achieve this flexibility through the adaptation of recent algorithms from the field of computer graphics to the specific requirements of geological modelling, specifically the representation of non-manifold topologies and sharp features. We combine the method with a swarm optimization approach to enable the automatic determination of vertex position and crease sharpness values. The result of this work is implemented in an open-source software (PySubdiv) for reconstructing geological structures while resulting in a model which is (1) sealed/watertight, (2) controllable with a control mesh, and (3) topologically similar to the main geological structure. Also, the reconstructed model may include a fewer number of vertices compared to the input geological structure which results in reducing the cost of modelling and simulation. Furthermore, the proposed method resolves some problems known from spline surfaces. In addition to enabling a manual adjustment of sealed geological models, the algorithm also provides a method for the integration of explicit surface representations in inverse frameworks and the consideration of uncertainties.