=== Computational Domain & Global Ground ===
The SBR simulation engine requires a finite computational domain. All the stray rays that hit the boundaries of 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.
The size of the Ray domain is specified in terms of six '''Offset''' [[parameters]] along the ±X, ±Y and ±Z directions. The default value of all these six offset [[parameters]] is 10 project units. You can To change them arbitrarily. After changing these values, use the '''Apply''' button to make the changes effective while the dialog is still open.You can change the size and color of the ray domain box through the Ray Domain Settings Dialogsettings, which can be accessed in one of follow the following three waysprocedure below:
# Click * Open the Ray Domain Settings Dialog by clicking the '''Domain''' [[File:image025.jpg]] button of the Simulation Toolbar.# Select the '''SimulateToolbar''' > , or by selecting '''Menu > Simulate > Computational Domain''' > '''> Settings...''' item of the Simulate Menu.# Right click , or by right-clicking on the '''Ray Domain''' item of the Navigation Tree navigation tree and select selecting '''Domain Settings...'''# Use from the contextual menu, or simply using the keyboard shortcut '''{{key|Ctrl + A}}.* The size of the Ray domain is specified in terms of six '''Offset''' [[parameters]] along the ±X, ±Y and ±Z directions. The default value of all these six offset [[parameters]] is 10 project units. Change these values as you like.* You can also change the color of the domain box using the {{ket|Color}} button.* After changing the settings, use the {{key|Apply}} button to make the changes effective while the dialog is still open.
Most outdoor and indoor propagation scenes include a flat ground at their bottom, which bounces incident rays back into the scene. [[EM.Cube]]'s [[Propagation Module]] 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. '''Do not forget to disable the global ground if you want to model a free space propagation scene.'''