EM.Terrano Tutorial Lesson 6: Modeling Irregular Terrain
What You Will Learn
In this tutorial you will use a wizard to create a plateau terrain profile. You will learn the special properties of terrain objects affecting the elevation of objects above them.
Creating the Plateau Terrain Profile
For this tutorial lesson, you will use a wizard to create a large terrain profile in the project workspace. Click on the Plateau Terrain Wizard button of the Wizard Toolbar or select the menu item Tools → Propagation Wizards → Plateau Terrain. A large plateau terrain object appears with a random rough surface.
Just like impenetrable and penetrable surfaces, a terrain surface is a special type of object in EM.Terrano that is used to model non-flat or irregular ground. Terrain objects are grouped together under Terrain Surfaces node of "Physical Structure" in the navigation tree. Open the variables dialog and see all the variables defined by the wizard for the plateau terrain scene. Edit and change the definition of the following variables:
|Variable Name||Original Definition||New Definition|
Constructing Blocks of Buildings
Create a default impenetrable surface group in the navigation tree with brick composition. Then, under "Block_1" draw two box objects withe following parameters:
|Object||Geometry||Block Group||Surface Type||Material||Dimensions||Location Coordinates||Rotation Angles|
|Box_1||Box||Block_1||Impenetrable surface||Brick||80m × 40m × 20m||(320m, 240m, 0)||(0°, 0°, 0°)|
|Box_2||Box||Block_1||Impenetrable surface||Brick||40m × 80m × 20m||(-300m, -300m, 0)||(0°, 0°, 0°)|
In Tutorial Lesson 1 you learned how to create an array of point objects. In this lesson, you build an array of box objects to model a block of buildings. Select Box_2 and click the Array button of the Tools Toolbar, or simply use the keyboard shortcut A. The Array Dialog opens up. Enter 3, 2 and 1 for the Element Count along the X, Y and Z directions, respectively. Enter 100m, 120m and 0 for Spacing along the three axes, respectively. The table below summarizes the array properties:
|Array Object||Parent Object||X Count||Y Count||Z Count||X Spacing||Y Spacing||Z Spacing|
At this point, your physical scene should look like the figure below:
The most important property of terrain objects in EM.Terrano is that they can (optionally) affect the elevation of objects placed on them. Otherwise, from a modeling point of view, terrain objects behave like impenetrable surface. Open the property dialog of the Impenetrable Surface group "Block_1", and check the box labeled Adjust Blocks to Terrain Elevation.
As soon as you close the impenetrable surface block's property dialog, you will notice that the building objects are lifted up and placed on the surface of the terrain.
It is worth examining the mesh of your scene at this time. A terrain surface is a tessellated surface object, which consists of a large number of triangular cells. View the mesh of your physical structure to get a sense of its geometrical complexity.
Defining the Transmitter & Receivers
For this tutorial lesson, use the Basic Link Wizard to create a vertically polarized half-wave dipole transmitter and a grid of isotropic receivers. Set the Grid Extents equal to 800m, and keep the default values of the other parameters, i.e., a transmitter height of 10m, receiver height of 1.5m and receiver spacing of 5m. The transmitter base location point called "TXP" is originally positioned at (0, 0, 10m). Change its coordinates to (100m, 100m, 10m). At this time the transmitter is hidden under the terrain, and so are a large number of receivers.
Similar to building blocks, a terrain surface can also (optionally) affect the elevation of the transmitters and receivers that are placed above it. Open the property dialogs of the transmitter and receiver sets and check the boxes labeled Adjust Tx Set to Terrain Elevation and Adjust Rx Set to Terrain Elevation, respectively. In the case of the receiver set, also check the box labeled Display Small Rx Points at the bottom of the dialog.
At this time, your project workspace must show a scene like the figure below.
|The Z-coordinate of a transmitter or a receiver located above a terrain surface is adjusted to the sum of its original height and the terrain elevation at its base location.|
To get a better view of the relative position of the tranmsitter and receivers and their corresponding base location points, click the Right View button of the View Toolbar to see a side view of your propagation scene.
Running an SBR Analysis of the Propagation Scene with the Plateau Terrain
Run a single-frequency SBR simulation of your plateau terrain scene and visualize its received power coverage map. You can see from the figure below that the upper portion of the plateau obstructs many direct rays from reaching the valley region. As a result, the reception around the building array is not good.
Now open the simulation run dialog and click the Settings button next to the simulation engine type drop-down list. This opens up EM.Terrano's Ray Tracing Engine Settings dialog. Uncheckmark "Include edge diffraction" checkbox and a new SBR analysis. You will see that there is no reception behind the buildings.
To improve the reception, you can bring the transmitter to the edge of the plateau. Keep in mind that to move a transmitter or receiver, you need to move their associated based point sets. Change the coordinates of the base point "TXP" to X = Y = 30mm. Keep the original Z-coordinate of 10m. Now make sure to checkmark "Include edge diffraction" checkbox and run a new SBR analysis of the scene and visualize its coverage map. You will see that the valley region now gets considerable reception.
The coverage can be further improved by raising the height of the transmitter above the terrain surface. Remember that the height of the transmitter was parameterized by the basic link wizard. Open the variables dialog and change the value of "Tx_h" to 20m.
Run a new SBR simulation. Visualize the received power coverage map and see the improvement in reception due to the increased height of the transmitter.
Changing the Terrain's Surface Roughness Statistics
Among the variables that the wizard initiated are root-mean-square (RMS) height and correlation length of the rough surface. The terrain surface object is assumed to have an additional offset elevation that is represented by the variable called "elevation". Open the variables dialog and change the definition of the following parameters:
|Variable Name||Original Definition||New Definition|
As you can see from the following figure, the new roughness statistics make the terrain more rugged than before.
Run an SBR analysis of the new rugged terrain scene. Note that this is a relatively large computational problem. The simulation output window reports some of the simulation parameters:
|SBR Simulation Parameter||Value|
|Total Number of Facets||62,066|
|Total Number of Edges||39,680|
|Total Number of Receivers||25,921|
|Total Number of Transmitted Rays||64,980|
At the end of the SBR simulation, visualize the coverage map. Note how the rugged terrain surface has caused significant wave diffusion throughout the scene.