== Building a Propagation Scene ==
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=== The different Elements of a Propagation Scene ===
A typical propagation scene in EM.Terrano consists of several elements. At a minimum, you need a transmitter (Tx) at some location to launch rays into the scene and a receiver (Rx) at another location to receive and collect the incoming rays. A transmitter and a receiver together make the simplest propagation scene, representing a free-space line-of-sight (LOS) channel. A transmitter is one of EM.Terrano's several source types, while a receiver is one of EM.Terrano's several observable types. A simpler source type is a Hertzian dipole representing an almost omni-directional radiator. A simpler observable is a field sensor that is used to compute the electric and magnetic fields on a specified plane.
[[Image:PROP4.png|thumb|400px|EM.Terrano's Global Ground Settings dialog.]]
=== Understanding the Why Do You Need a Finite Computational Domain & Global Ground ? ===
The SBR simulation engine requires a finite computational domainfor ray termination. All the stray rays that emanate from a source inside this finite domain and hit its boundaries are terminated during the simulation process. Such rays exit the computational domain and travel to the infinity, with no chance of ever reaching any receiver in the scene. When you define a propagation scene with various elements like buildings, walls, terrain, etc., a dynamic domain is automatically established and displayed as a green wireframe box that surrounds the entire scene. Every time you create a new object, the domain box is automatically adjusted and extended to enclose all the objects in the scene.
To change the ray domain settings, follow the procedure below:
* You can also change the color of the domain box using the {{key|Color}} button.
* After changing the settings, use the {{key|Apply}} button to make the changes effective while the dialog is still open.
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=== Understanding the Global Ground ===
Most outdoor and indoor propagation scenes include a flat ground at their bottom, which bounces incident rays back into the scene. EM.Terrano provides a global flat ground at z = 0. The global ground indeed acts as an impenetrable surface that blocks the entire computational domain from the z = 0 plane downward. It is displayed as a translucent green plane at z = 0 extending downward. The color of the ground plane is always the same as the color of the ray domain. The global ground is assumed to be made of a homogeneous dielectric material with a specified permittivity ε<sub>r</sub> and electric conductivity σ. By default, a rocky ground is assumed with ε<sub>r</sub> = 5 and σ = 0.005 S/m. You can remove the global ground, in which case, you will have a free space scene. To disable the global ground, open up the "Global Ground Settings" dialog, which can be accessed by right clicking on the '''Global Ground''' item in the Navigation Tree and selecting '''Global Ground Settings... '''Remove the check mark from the box labeled '''"Include Half-Space Ground (z<0)"''' to disable the global ground. This will also remove the green translucent plane from the bottom of your scene. You can also change the material properties of the global ground and set new values for the permittivity and electric conductivity of the impenetrable, half-space, dielectric medium.
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Alternatively, you can use EM.Terrano's '''Empirical Soil Model''' to define the material properties of the global ground. This model requires a number of [[parameters]]: Temperature in °C, and Volumetric Water Content, Sand Content and Clay Content all as percentage.
{{Note|To model a free-space propagation scene, you have to disable EM.Terrano's default global ground.}}