Representation: 3-D

3-D modeling has been the subject of increased attention in the last two decades. Technology has been developed to such a degree that large datasets can be collected, processed, analyzed, managed, and visualized in reasonable time. Domain applications are looking with much interest at 3-D representations, acknowledging the increased possibilities for display and analysis of data. The tendency of using 3-D data from different domains in one application is growing, and this poses many challenges. Developed independently through the years, 3-D applications involve various representations (vector, raster, freeform curves, and surfaces), levels of detail, appearance, semantics, and topology. Representing the real world in 3-D differs significantly from representation in 2-D. Technology and approaches for data collection (detect vertical elements of objects, overhanging sections – as sheds, bridges, and roofs), data processing, data structures, data models, and visualization have to be adapted, extended, and/or improved to deal with vertical and overhanging elements as well as objects located inside, above or below each other. Many of the well-known approaches in 2-D GIS are not readily applicable to 3-D representation. This requires investigation of new possibilities for representation, structuring, and visualization of data. This entry outlines the most commonly used 3-D geometric representations in terms of their geometry, resolution, topology, and semantics, elaborates on their use in a wide range of applications, and discusses some of the challenges in research and development.