== Creating & Analyzing a Semi-Random City Propagation Scene ==
For this tutorial lesson, you will use a wizard to build the geometry of an urban environment. Click on the <b>Random City Wizard</b> [[Image:RandomCityWizardIcon.png]] button of the Wizard Toolbar or select the menu item '''Tools → Propagation Wizards → Random City'''. A dialog pops up and asks for the total city extents and number of buildings. Select <b>Custom</b> option for “Select Scene Type”. Reduce the “City Extents” to 250 and accept the default value of 25 for the total number of buildings in the scene. Change the Max Building Base Size to 20 and press the {{key|OK}} button. The wizard creates 25 buildings with random locations and random dimensions in an area of 250m × 250m centered at the origin of coordinates.
Since the location of the buildings is totally random, there is a chance that your transmitter may fall inside an "impenetrable" building and becomes useless. In that case, you may change the location of your transmitter or repeat this process until you get an acceptable scene.
== Exporting Your Urban Canyon Scene ==
A fully random city scene changes very quickly with few mouse clicks. This is helpful at the beginning when updating the random variables until you get a desirable scene. After that, the random feature may not be useful. [[EM.Cube]] allows you to export your physical structure to a number of popular CAD file formats such as STEP, IGES, STL, <i>etc</i>. The STEP and IGES options export all the solid, surface, curve and point objects. The STL format exports only solid and surface objects as sets of interconnected triangles and ignores all the curve or point objects. This is more suitable for propagation scenes if you don't want to exports all the base location pointspoint radiators. CubeCAD is the module where import and export operations should normally take place. For convenience, you can export your physical structure from any module including [[EM.Terrano]]. However, you can import external files only to CubeCAD.
In the case of stereolithography (STL) file export, [[EM.Cube]] offers two options: ASCII STL and Binary STL. The latter format results in a more compact file. You can generate a triangular surface mesh of objects in CubeCAD. This mesh is what is exported as the STL file. [[EM.Cube]] allows you to control the shape and size of the triangular patches that are used to model your objects. Switch to CubeCAD by clicking its button at the top of the navigation tree. Then, clicking the <b>Mesh Settings</b> [[Image:fdtd_meshsettings.png]] button of the Simulate Toolbar in CubeCAD or use the keyboard shortcut {{key|Ctrl+G}} to open the CAD Mesh Settings Dialog. Change the value of '''Mesh Cell Size''' to 100 units. This will generate very large triangular patches or cells. The parameter '''Mesh Cell Size''' is the counterpart of '''Cell Edge Length''' in [[EM.Terrano]]'s SBR Mesh Settings dialog, which you already encountered in Tutorial Lesson 3.