=== Terrain Surfaces vs. Global Ground ===
[[File:PROP16.png|thumb|200px|[[Propagation Module]]'s Terrain dialog]]
A terrain surface acts as a custom, unlevel or irregular ground for your propagation scene. EM.Cube's default global ground blocks the z < 0 half-space everywhere in the computational domain. You can simply turn off the global ground and create one or more terrain objects and place them arbitrarily in the scene. You can also import an external terrain model or file. A terrain represents an impenetrable surface with a more complex surface profile. You can have one or more terrain objects of finite extents and place them on or above the global ground.
* Similar to other blocks, you have to specify the material properties, Permittivity (ε<sub>r</sub>) and Electric Conductivity (σ), of the terrain group. Rock with ε<sub>r</sub> = 5 and σ = 0.005 S/m is the default material choice for a new terrain.
* Click the '''OK''' button of the dialog to accept the changes and close it.
[[File:PROP16.png]]
Figure 1: [[Propagation Module]]'s Terrain dialog.
You can change the properties of a terrain surface group from its property dialog. Click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog, which is identical to the case of impenetrable surfaces. You can also use EM.Cube's Material List, which will be explained later. When a new terrain type is created, its node on the Navigation Tree becomes active. Under this node you can create and add new terrain objects. When a terrain node is active for drawing, all CAD object creation tools are disabled. You have three options for creating a new terrain object, which will be described in detail in the next sections of this manual: