Decoupling Mesh and Data Representations for Geo-spatial Data Visualization

Nowadays, data visualization plays an important role in geo-spatial data investigations, speci cally in the context of visual exploration at interactive frame rates. Geo-spatial data typically include geographic information in form of a set of gridded or un-gridded points, where each point identies a location on the earth's surface. A variety of projection methods are in use to re-produce the location of a speci c data point. For example, in contrast to the longitude/latitude projection system, the UTM (Universal Transverse Mercator) system provides a conformal projected location of the earth based on a non-linear scaling in both easting and northing. In this work, geo-spatial data such as terrain or ocean oor data are represented as 2D coordinates, e.g., longitude/latitude, and a number of associated attributes of measured information such as depth or height, backscattering, sub-bottom pro le information, etc. Both main and graphical memory capacities are steadily increasing, but so are data sizes. Hence, current and future storage capacities still lack the ability to handle the targeted enormous data sizes with proper efficiency. To allow for interactive exploration, the number of rendered objects in most dynamic approaches is obligated to be below a certain complexity at run time. Ful lling such goals requires several techniques to be integrated in our data exploration approach. View-dependency, LOD (level of detail) representations, and multi-resolution methods form the basis to tackle the objects redundancy, dynamic data updates, and simplification. Existing approaches can be classi ed into two main groups, the ones that operate on irregular triangular meshes and the ones that operate on regular grids. While irregular triangular meshes can provide better adaptivity, regular grids can be handled more effciently. Our approach is to decouple mesh and data representations such that data management is performed effciently on regular grids while mesh rendering is executed using a fixed adaptive triangular mesh in parameter plane. The triangular mesh is optimized with respect to the projected triangle sizes and shapes. During interaction we update the mesh by merely adjusting the vertices' heights, which are queried from an underlying multi-resolution grid structure. The triangular mesh and the multi-resolution grid structure are precomputed and cached on the GPU. A tiling strategy is employed for the grid structure. We are able to generate very high frame rates using triangles with optimized shape in a high-quality rendering. Our approach is applied to di erent data types as inputs such as terrain data and bathymetry data. Terrain data include heightfield and color information that is acquired using aerial instruments. From the given data, hierarchies are generated in a pre-processing step. Bathymetry data are acquired using multibeam sonar. The measured data include information on the structure and nature of the ocean floor and gas maps underneath the ocean surface. Data exploration, ocean floor rendering, and further data visualization methods are employed in an interactive system. Our work provides highperformance algorithms and evaluates them utilizing synthetic as well as real data from both terrain and bathymetry measurements. Our contribution in the terrain or ocean floor rendering field is providing a new and fast method for height eld exploration and rendering with frame rates exceeding those of most state-of-the-art approaches while providing optimal triangle shapes. In particular, using a fixed mesh, some interactive operations do not require data updates. Moreover, the interactive visual system comprises visualization of backscatter and water column data incorporated in the final rendering scene, which is a novel visualization task that has not yet been tackled by the existing 3D visualization systems for bathymetry data such as Fledermaus.