By default, the polygon will drape over the globe surface like a blanket. Close ArcMap and open the ArcGlobe Overpass.3dd file.(The completed polygon feature is overpass_ply and is included in Overpass.gdb.) After adding the imagery file in the Overpass geodatabase to an ArcMap document, create a simple rectangular shape and ensure that there are small areas of overlap at each end of the overpass. Later, this polygon will be extruded to create a 3D volume for the overpass. The first step is to create a polygon feature using ArcMap in universal transverse Mercator (UTM) Zone 18N.Section 1: Create a 3D Multipatch from an Extruded Polygon SketchUp will be used to apply imagery to the top of the 3D overpass model.įigure 4: To determine the elevation of the overpass once it's extruded, sample the value of the DEM on each end of the roadway (as indicated by the ovals). This process requires a polygon file and a swatch of high-resolution imagery.
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Instead of editing the DEM, this tutorial will show how to create a simple but realistic-looking overpass as a 3D multipatch feature that spans the gap and has a void space underneath. Although this fixes the elevation of the overpass road, it creates an impenetrable wall in the underlying expressway.
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One approach to correcting this situation might be to edit the DEM or add a patch to raise that road and create a flat surface. Lower-resolution DEMs, by comparison, just make features look flat. This type sampling error is commonly seen in high-resolution DEMs in urban environments that show overlapping roadways and structures of different elevations. This exercise starts with an overpass feature that has been poorly captured by the existing 1-meter (m) digital elevation model (DEM) for downtown Philadelphia as shown in Figure 1.
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zip file on įigure 2 (left): Add the polygon feature created in ArcMap to Overpass.3dd.įigure 3 (right): By default, the polygon will drape over the globe surface like a blanket.
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To complete this exercise, the following software and data are required Some familiarity with Google SketchUp may also be helpful.
It's assumed that the reader is familiar with ArcGIS Desktop applications and the ArcGIS 3D Analyst extension, including ArcGlobe. The workflow outlined will familiarize the reader with tools in ArcGIS 10 for importing, exporting, and placing different types of 3D features. It uses a geometrically simple urban feature-a freeway overpass in downtown Philadelphia-and starts with a polygon and some high-resolution aerial imagery. This exercise walks the reader through the process of creating and adding texture to a 3D multipatch feature.
ArcGIS 10 introduces a host of new 3D data management and analysis capabilities that enhance 3D analysis. The multipatch, Esri's native 3D feature type, is a key element whether working in ArcGlobe or ArcScene. The 3D virtual city is emerging as an essential GIS tool for visualization and analysis in the urban environment-from placing a proposed building construction in the context of its surroundings to conducting analyses in three dimensions such as line-of-sight or 3D volumetric shadows. Figure 1: This exercise shows how to correct this sampling error, commonly seen in high-resolution DEMs in urban environments.
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