Towards a 3D Feature Overlay through a Tetrahedral Mesh Data Structure

The use of 3D features within GIS has been increasing due to the need to represent, query, manipulate, and analyze man-made objects in relationship to other 3D features related to the surface of the earth. This will yield an increased use of 3D boundary representations of the features. The spatial relationship between two or more features is often evaluated using a geometrical overlay of these features, which reveals whether these features overlap and—if they do—to which extent. We present the design of a 3D overlay algorithm which overlays 3D triangulated boundary representations through a constrained tetrahedral mesh. The intersections between the constrained facets of the 3D features are calculated on the fly and within a restricted neighborhood. We can identify and reconstruct the overlaid parts of the 3D boundary representation within the tetrahedral mesh. The implementation is based on the Computational Geometry Algorithms Library, which proved to have the functionality needed but also has its limitations.     

Complexity and Intractability: Limitations to Implementation in Analytical Cartography

The computational complexity of algorithms is an important consideration for all computer systems, including geographic information systems and mapping systems. Mathematical cartographers and GIS professionals need to understand and to take into account the limitations imposed on problem solving by the very nature of computation itself. We look at three active research sub-areas of analytical cartography to highlight the differences between traditional mathematical solutions and solutions with computationally tractable algorithms. The three sub-areas are map projections, map feature labeling, and map generalization.     

Report on Cartographic and GIS Activity in the U.S. Fish and Wildlife Service

The U.S. Fish and Wildlife Service (FWS) is a federal agency whose mission is, working with others, to conserve fish and wildlife and their habitats for the continuing benefit of the American people. Under the management of fish and wildlife professionals, the National Wildlife Refuge System has become the world's premier network of wildlife habitats. The FWS is making use of modern cartographic methods and implementing Geographic Information Systems to more effectively manage the lands and resources entrusted to them.