Answering Real-World QUESTIONS Continued from page 8 Certain base data is required to analyze this problem: an elevation surface, the proposed flight path, locations of threats, and information about the effective range of each threat. To translate these requirements into GIS terms, you will need an elevation surface such as a raster digital elevation model (DEM), a triangulated irregular network (TIN), or a terrain dataset; a 3D line feature class that describes the proposed route(s); and a 2D (or 3D) point feature class that conconstruction of threat dome features using the following workflow. 1. In the ArcScene application in 3D Analyst, add the point feature class twice to create two layers in the table of contents. 2. Set the symbology for each layer to Simple Marker Symbol > Sphere. 3. Set the Advanced > Size value for one layer to InnerThreatDistance and the other to OuterThreatDistance. 4. Use the Layer 3D To Feature Class geoSkyline tool generates the visible horizon for each threat position. The Skyline Barrier tool can effectively project this horizon up into the sky, displaying the results as a volume representation of the visible airspace above each threat point. Intersecting these volumes with the pure distance-based threat spheres generates danger zones that incorporate both visibility and lethal ranges. To identify which sections of the proposed route intersect the 3D danger zones, use the Intersect Line With Multipatch tool. It splits the route into sections of low, medium, and high risk. The 3D distances of each segment can be easily calculated using the Calculate Geometry option for a field or the Add Z Information tool. This exposes information that will be summarized into graphs. For example, one graph could summarize the overall risk, while another could display the flight path as ordered stretches of risk. Repeating this analysis for multiple proposed routes and comparing the resulting graphs can help select the best route. Advanced users can expand this analysis How tall can the buildings located in the orange area be and still remain unseen from the blue viewpoints? Use the Skyline and Skyline Barrier tools to calculate a barrier or fan that separates the ground from the sky from each viewpoint. tains attributes for threats. This example uses a 5-meter raster DEM. In the first step, the 2D point features are converted to quantifiable threat domes. This example has three antiaircraft (AA) gun positions. Each AA gun has different effective ranges depending on the presence or absence of radar assistance. The outer zone (where radar assistance is required) is less dangerous than the inner zone because the plane's countermeasures are more effective. This information can be converted into threat domes (which are more easily understood) using feature attributes to drive the 10 ArcUser Fall 2010 processing tool to convert these symbolized layers into volumes and store them as multipatch features in two new feature classes. Layer transparency and layer rendering priority provide the framework for seeing these nested/overlapping threat domes in a three-dimensional view. Although these threat domes are useful, they do not take into account one of the most useful factors when trying to protect planes from antiaircraft fire—the terrain. The Skyline and Skyline Barrier tools can help incorporate terrain into this analysis. The www.esri.com