CRUSTA: A NEW VIRTUAL GLOBE ENABLING REMOTE GEOLOGIC MAPPING

Virtual globes are becoming ubiquitous for visualizing the Earth and other planets. Although many current virtual globes have proven quite useful for data visualization, they were never designed to support remote geologic investigation. Their shortcomings have become more obvious as earth scientists struggle to visually explore and interpret digital elevation models (DEM) and imagery data with sub-meter pixel resolution spanning large areas (>2000 km²). In response, we developed Crusta as an alternative virtual globe that allows users to investigate such data by conducting interactive, real-time, virtual field mapping. Crusta represents the globe as a 30-sided polyhedron to avoid distortion of the display, in particular the singularities at the poles characteristic of other projections. Each side can be subdivided to an arbitrarily fine grid on the surface of the globe to accommodate input DEM and image data of arbitrary resolution, from global (e.g., BlueMarble) to local (e.g., DEMs from tripod LiDAR). We designed Crusta with a focus on dynamic, interactive exploration of surface data by the user. By using multi-resolution, view-dependent, out-of-core algorithms, Crusta enables real-time, interactive visualization and analysis of massive terrain data sets on a range of platforms from laptops to immersive geowalls and caves. A convenient pre-processing tool based on the GDAL library facilitates importing a number of data formats into the Crusta-specific multi-scale hierarchical format. Shading is computed on-the-fly and the globe's surface can be exaggerated vertically with real-time feedback. The combination of the two effects greatly improves the perception of the shape of surface topography. Color maps associated with the elevation values can be created, modified and applied interactively. This functionality allows the generation of topographic contours that can be adjusted dynamically as an additional tool for discovery. Beyond exploration, Crusta enables real-time generation, editing and display of georeferenced vector lines annotated with geological map symbols directly on the virtual 3D landscape. Crusta enables remote virtual geologic studies that replicate and expand upon field-based observations by allowing operations that are impossible in the field.