</tr>
</table>
== Discretizing the Propagation Scene in EM.Terrano ==
=== Why Do You Need to Discretize the Scene? ===
[[EM.Terrano]]'s SBR solver uses a method known as Geometrical Optics (GO) in conjunction with the Uniform Theory of Diffraction (UTD) to trace the rays from their originating point at the source to the individual receiver locations. Rays may hit obstructing objects on their way and get reflected, diffracted or transmitted. [[EM.Terrano]]'s SBR solver can only handle diffraction off linear edges and reflection from and transmission through planar interfaces. When an incident ray hits the surface of the obstructing object, a local planar surface assumption is made at the specular point. The assumptions of linear edges and planar facets are valid in in the case of a scene with cubic buildings and a flat global ground.
In many practical scenarios, however, your buildings may have curved surfaces, or the terrain may be irregular. [[EM.Terrano]] allows you to draw any type of surface or solid geometric objects such as cylinders, cones, etc. under impenetrable and penetrable surface groups or penetrable volumes. [[EM.Terrano]]'s mesh generator creates a triangular surface mesh of all the objects in your propagation scene, which is called a facet mesh. Even the walls of cubic buildings are meshed using triangular cells. This enables [[EM.Terrano]] to properly discretize composite buildings made of conjoined cubic objects.
Unlike [[EM.Cube]]'s other computational modules, the density or resolution of [[EM.Terrano]]'s surface mesh does not depend on the operating frequency and is not expressed in terms of the wavelength. The sole purpose of [[EM.Terrano]]'s facet mesh is to discretize curved and irregular scatterers into flat facets and linear edges. Therefore, geometrical fidelity is the only criterion for the quality of a facet mesh. It is important to note that discretizing smooth objects using a triangular surface mesh typically creates a large number of small edges among the facets that are simply mesh artifacts and should not be considered as diffracting edges. For example, each rectangular face of a cubic building is subdivided into four triangles along the two diagonals. The four internal edges lying inside the face are obviously not diffracting edges. A lot of subtleties like these must be taken into account by the SBR solver to run accurate and computationally efficient simulations.
=== Generating the SBR Mesh ===
You can view and examine the discretized version of your scene objects as they are sent to the SBR simulation engine. You can adjust the mesh resolution and increase the geometric fidelity of discretization by creating more and finer triangular facets. On the other hand, you may want to reduce the mesh complexity and send to the SBR engine only a few coarse facets to model your buildings. The resolution of [[EM.Terrano]]'s facet mesh generator is controlled by the '''Mesh Cell Size''' parameter, which is expressed in project length units. The default mesh cell size of 100 units might be too large for non-flat objects. You may have to set a smaller mesh cell size in [[EM.Terrano]]'s Mesh Settings dialog, along with a lower curvature angle tolerance value to capture the curvature of your curved structures adequately.
<table>
<tr>
<td>
[[Image:prop_manual-29.png|thumb|left|480px|EM.Terrano's mesh settings dialog.]]
</td>
</tr>
</table>
[[Image:Info_icon.png|30px]] Click here to learn more about '''[[Preparing_Physical_Structures_for_Electromagnetic_Simulation#Working_with_EM.Cube.27s_Mesh_Generators | Working with Mesh Generator]]'''.
[[Image:Info_icon.png|30px]] Click here to learn more about the properties of '''[[Glossary_of_EM.Cube%27s_Simulation-Related_Operations#Facet_Mesh | EM.Terrano's Facet Mesh Generator]]'''.
<table>
<tr>
<td> [[Image:PROP MAN9.png|thumb|left|640px|The facet mesh of the buildings in the urban propagation scene generated by EM.Terrano's Random City wizard.]] </td>
</tr>
</table>
== Running SBR Simulations in EM.Terrano ==
=== SBR Simulation Types ===
Once you have set up your propagation scene in [[EM.Terrano]] and have defined sources/transmitters and observables/receivers for your scene, you are ready to run a SBR ray tracing simulation. [[EM.Terrano]] offers thee simulation modes:
{| class="wikitable"
|-
! scope="col"| Simulation Mode
! scope="col"| Usage
! scope="col"| Number of Engine Runs
! scope="col"| Frequency
! scope="col"| Restrictions
|-
| style="width:120px;" | [[#Running a Single-Frequency SBR Analysis | Single-Frequency Analysis]]
| style="width:250px;" | Simulates the propagation scene "As Is"
| style="width:100px;" | Single run
| style="width:150px;" | Runs at the center frequency fc
| style="width:100px;" | None
|-
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Frequency_Sweep_Simulations_in_EM.Cube | Frequency Sweep]]
| style="width:250px;" | Varies the operating frequency of the ray tracer
| style="width:100px;" | Single ray tracing run, multiple frequency computations
| style="width:150px;" | Runs at a specified set of frequency samples
| style="width:100px;" | None
|-
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Parametric_Sweep_Simulations_in_EM.Cube | Parametric Sweep]]
| style="width:250px;" | Varies the value(s) of one or more project variables
| style="width:100px;" | Multiple runs
| style="width:150px;" | Runs at the center frequency fc
| style="width:100px;" | None
|}
You set the simulation mode in [[EM.Terrano]]'s simulation run dialog. A single-frequency analysis is a single-run simulation. The two other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain parameters are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.
{{Note| [[EM.Terrano]]'s frequency sweep simulations are very fast because the geometrical optics (ray tracing) part of the simulation is frequency-independent.}}
=== Running a Single-Frequency SBR Analysis ===
A single-frequency SBR analysis is the simplest type of ray tracing simulation and involves the following steps:
* Set the units of your project and the frequency of operation. Note that the default project unit is '''millimeter'''. Wireless propagation problems usually require meter, mile or kilometer as the project unit.
* Create the blocks and draw the buildings at the desired locations.
* Keep the default ray domain and accept the default global ground or change its material properties.
* Define an excitation source and observables for your project.
* If you intend to use transmitters and receivers in your scene, first define the required base sets and then define the transmitter and receiver sets based on them.
* Run the SBR simulation engine.
* Visualize the coverage map and plot other data.
You can access [[EM.Terrano]]'s Simulation Run dialog by clicking the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or by selecting '''Simulate > Run...''' or using the keyboard shortcut {{key|Ctrl+R}}. When you click the {{key|Run}} button, a new window opens up that reports the different stages of the SBR simulation and indicates the progress of each stage. After the SBR simulation is successfully completed, a message pops up and prompts the completion of the process.
<table>
<tr>
<td>
[[Image:Terrano L1 Fig16.png|thumb|left|480px|EM.Terrano's simulation run dialog.]]
</td>
</tr>
</table>
<table>
<tr>
<td>
[[Image:PROP MAN10.png|thumb|left|550px|EM.Terrano's output message window.]]
</td>
</tr>
</table>
=== Changing the SBR Engine Settings ===
There are a number of SBR simulation settings that can be accessed and changed from the SBR Settings Dialog. To open this dialog, click the button labeled {{key|Settings}} on the right side of the '''Select Engine''' drop-down list in the Run Dialog. [[EM.Terrano]]'s SBR simulation engine allows you to separate the physical effects that are calculated during a ray tracing process. You can selectively enable or disable '''Reflection/Transmission''' and '''Edge Diffraction''' in the "Ray-Block Interactions" section of this dialog. By default, the reflection, transmission and edge diffraction effects are enabled and the terrain diffraction effects are disabled. Separating these effects sometimes help you better analyze your propagation scene and understand the impact of various blocks in the scene.
[[EM.Terrano]] allows a finite number of ray bounces for each original ray emanating from a transmitter. This is very important in situations that may involve resonance effects where rays get trapped among multiple surfaces and may bounce back and forth indefinitely. This is set using the box labeled "'''Max No. Ray Bounces'''", which has a default value of 10. Note that the maximum number of ray bounces directly affects the computation time as well as the size of output simulation data files. This can become critical for indoor propagation scenes, where most of the rays undergo a large number of reflections. Two other parameters control the diffraction computations: '''Max Wedge Angle''' in degrees and '''Min Edge Length''' in project units. The maximum wedge angle is the angle between two conjoined facets that is considered to make them almost flat or coplanar with no diffraction effect. The default value of the maximum wedge angle is 170°. The minimum edge length is size of the common edge between two conjoined facets that is considered as a mesh artifact and not a real diffracting edge. The default value of the minimum edge length is 5 project units.
<table>
<tr>
<td>
[[Image:PROP MAN11.png|thumb|left|720px|EM.Terrano's SBR simulation engine settings dialog.]]
</td>
</tr>
</table>
As rays travel in the scene and bounce from surfaces, they lose their power, and their amplitudes gradually diminish. From a practical point of view, only rays that have power levels above the receiver sensitivity threshold can be effectively received. Therefore, all the rays whose power levels fall below a specified power threshold are discarded. The '''Ray Power Threshold''' is specified in dBm and has a default value of -100dBm. Keep in mind that the value of this threshold directly affects the accuracy of the simulation results as well as the size of the output data file.
You can also set the '''Angular Resolution''' of the transmitter rays in degrees. By default, every transmitter emanates equi-angular ray tubes at a resolution of 1 degree. Lower angular resolutions larger than 1° speed up the SBR simulation significantly, but they may compromise the accuracy. Higher angular resolutions less than 1° increase the accuracy of the simulating results, but they also increase the computation time. The SBR Engine Settings dialog also shows the required '''Minimum Angular Resolution''' in degrees in a greyed-out box. This number is calculated based on the overall extents of your computational domain as well as the SBR mesh resolution. To see this value, you have to generate the SBR mesh first. Keeping the angular resolution of your project above this threshold value makes sure that the small mesh facets at very large distances from the source would not miss any impinging ray tubes during the simulation.
== Working with EM.Terrano's Simulation Data ==
</tr>
</table>
== Discretizing the Propagation Scene in EM.Terrano ==
=== Why Do You Need to Discretize the Scene? ===
[[EM.Terrano]]'s SBR solver uses a method known as Geometrical Optics (GO) in conjunction with the Uniform Theory of Diffraction (UTD) to trace the rays from their originating point at the source to the individual receiver locations. Rays may hit obstructing objects on their way and get reflected, diffracted or transmitted. [[EM.Terrano]]'s SBR solver can only handle diffraction off linear edges and reflection from and transmission through planar interfaces. When an incident ray hits the surface of the obstructing object, a local planar surface assumption is made at the specular point. The assumptions of linear edges and planar facets are valid in in the case of a scene with cubic buildings and a flat global ground.
In many practical scenarios, however, your buildings may have curved surfaces, or the terrain may be irregular. [[EM.Terrano]] allows you to draw any type of surface or solid geometric objects such as cylinders, cones, etc. under impenetrable and penetrable surface groups or penetrable volumes. [[EM.Terrano]]'s mesh generator creates a triangular surface mesh of all the objects in your propagation scene, which is called a facet mesh. Even the walls of cubic buildings are meshed using triangular cells. This enables [[EM.Terrano]] to properly discretize composite buildings made of conjoined cubic objects.
Unlike [[EM.Cube]]'s other computational modules, the density or resolution of [[EM.Terrano]]'s surface mesh does not depend on the operating frequency and is not expressed in terms of the wavelength. The sole purpose of [[EM.Terrano]]'s facet mesh is to discretize curved and irregular scatterers into flat facets and linear edges. Therefore, geometrical fidelity is the only criterion for the quality of a facet mesh. It is important to note that discretizing smooth objects using a triangular surface mesh typically creates a large number of small edges among the facets that are simply mesh artifacts and should not be considered as diffracting edges. For example, each rectangular face of a cubic building is subdivided into four triangles along the two diagonals. The four internal edges lying inside the face are obviously not diffracting edges. A lot of subtleties like these must be taken into account by the SBR solver to run accurate and computationally efficient simulations.
=== Generating the SBR Mesh ===
You can view and examine the discretized version of your scene objects as they are sent to the SBR simulation engine. You can adjust the mesh resolution and increase the geometric fidelity of discretization by creating more and finer triangular facets. On the other hand, you may want to reduce the mesh complexity and send to the SBR engine only a few coarse facets to model your buildings. The resolution of [[EM.Terrano]]'s facet mesh generator is controlled by the '''Mesh Cell Size''' parameter, which is expressed in project length units. The default mesh cell size of 100 units might be too large for non-flat objects. You may have to set a smaller mesh cell size in [[EM.Terrano]]'s Mesh Settings dialog, along with a lower curvature angle tolerance value to capture the curvature of your curved structures adequately.
<table>
<tr>
<td>
[[Image:prop_manual-29.png|thumb|left|480px|EM.Terrano's mesh settings dialog.]]
</td>
</tr>
</table>
[[Image:Info_icon.png|30px]] Click here to learn more about '''[[Preparing_Physical_Structures_for_Electromagnetic_Simulation#Working_with_EM.Cube.27s_Mesh_Generators | Working with Mesh Generator]]'''.
[[Image:Info_icon.png|30px]] Click here to learn more about the properties of '''[[Glossary_of_EM.Cube%27s_Simulation-Related_Operations#Facet_Mesh | EM.Terrano's Facet Mesh Generator]]'''.
<table>
<tr>
<td> [[Image:PROP MAN9.png|thumb|left|640px|The facet mesh of the buildings in the urban propagation scene generated by EM.Terrano's Random City wizard.]] </td>
</tr>
</table>
== Running SBR Simulations in EM.Terrano ==
=== SBR Simulation Types ===
Once you have set up your propagation scene in [[EM.Terrano]] and have defined sources/transmitters and observables/receivers for your scene, you are ready to run a SBR ray tracing simulation. [[EM.Terrano]] offers thee simulation modes:
{| class="wikitable"
|-
! scope="col"| Simulation Mode
! scope="col"| Usage
! scope="col"| Number of Engine Runs
! scope="col"| Frequency
! scope="col"| Restrictions
|-
| style="width:120px;" | [[#Running a Single-Frequency SBR Analysis | Single-Frequency Analysis]]
| style="width:250px;" | Simulates the propagation scene "As Is"
| style="width:100px;" | Single run
| style="width:150px;" | Runs at the center frequency fc
| style="width:100px;" | None
|-
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Frequency_Sweep_Simulations_in_EM.Cube | Frequency Sweep]]
| style="width:250px;" | Varies the operating frequency of the ray tracer
| style="width:100px;" | Single ray tracing run, multiple frequency computations
| style="width:150px;" | Runs at a specified set of frequency samples
| style="width:100px;" | None
|-
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Parametric_Sweep_Simulations_in_EM.Cube | Parametric Sweep]]
| style="width:250px;" | Varies the value(s) of one or more project variables
| style="width:100px;" | Multiple runs
| style="width:150px;" | Runs at the center frequency fc
| style="width:100px;" | None
|}
You set the simulation mode in [[EM.Terrano]]'s simulation run dialog. A single-frequency analysis is a single-run simulation. The two other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain parameters are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.
{{Note| [[EM.Terrano]]'s frequency sweep simulations are very fast because the geometrical optics (ray tracing) part of the simulation is frequency-independent.}}
=== Running a Single-Frequency SBR Analysis ===
A single-frequency SBR analysis is the simplest type of ray tracing simulation and involves the following steps:
* Set the units of your project and the frequency of operation. Note that the default project unit is '''millimeter'''. Wireless propagation problems usually require meter, mile or kilometer as the project unit.
* Create the blocks and draw the buildings at the desired locations.
* Keep the default ray domain and accept the default global ground or change its material properties.
* Define an excitation source and observables for your project.
* If you intend to use transmitters and receivers in your scene, first define the required base sets and then define the transmitter and receiver sets based on them.
* Run the SBR simulation engine.
* Visualize the coverage map and plot other data.
You can access [[EM.Terrano]]'s Simulation Run dialog by clicking the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or by selecting '''Simulate > Run...''' or using the keyboard shortcut {{key|Ctrl+R}}. When you click the {{key|Run}} button, a new window opens up that reports the different stages of the SBR simulation and indicates the progress of each stage. After the SBR simulation is successfully completed, a message pops up and prompts the completion of the process.
<table>
<tr>
<td>
[[Image:Terrano L1 Fig16.png|thumb|left|480px|EM.Terrano's simulation run dialog.]]
</td>
</tr>
</table>
<table>
<tr>
<td>
[[Image:PROP MAN10.png|thumb|left|550px|EM.Terrano's output message window.]]
</td>
</tr>
</table>
=== Changing the SBR Engine Settings ===
There are a number of SBR simulation settings that can be accessed and changed from the SBR Settings Dialog. To open this dialog, click the button labeled {{key|Settings}} on the right side of the '''Select Engine''' drop-down list in the Run Dialog. [[EM.Terrano]]'s SBR simulation engine allows you to separate the physical effects that are calculated during a ray tracing process. You can selectively enable or disable '''Reflection/Transmission''' and '''Edge Diffraction''' in the "Ray-Block Interactions" section of this dialog. By default, the reflection, transmission and edge diffraction effects are enabled and the terrain diffraction effects are disabled. Separating these effects sometimes help you better analyze your propagation scene and understand the impact of various blocks in the scene.
[[EM.Terrano]] allows a finite number of ray bounces for each original ray emanating from a transmitter. This is very important in situations that may involve resonance effects where rays get trapped among multiple surfaces and may bounce back and forth indefinitely. This is set using the box labeled "'''Max No. Ray Bounces'''", which has a default value of 10. Note that the maximum number of ray bounces directly affects the computation time as well as the size of output simulation data files. This can become critical for indoor propagation scenes, where most of the rays undergo a large number of reflections. Two other parameters control the diffraction computations: '''Max Wedge Angle''' in degrees and '''Min Edge Length''' in project units. The maximum wedge angle is the angle between two conjoined facets that is considered to make them almost flat or coplanar with no diffraction effect. The default value of the maximum wedge angle is 170°. The minimum edge length is size of the common edge between two conjoined facets that is considered as a mesh artifact and not a real diffracting edge. The default value of the minimum edge length is 5 project units.
<table>
<tr>
<td>
[[Image:PROP MAN11.png|thumb|left|720px|EM.Terrano's SBR simulation engine settings dialog.]]
</td>
</tr>
</table>
As rays travel in the scene and bounce from surfaces, they lose their power, and their amplitudes gradually diminish. From a practical point of view, only rays that have power levels above the receiver sensitivity threshold can be effectively received. Therefore, all the rays whose power levels fall below a specified power threshold are discarded. The '''Ray Power Threshold''' is specified in dBm and has a default value of -100dBm. Keep in mind that the value of this threshold directly affects the accuracy of the simulation results as well as the size of the output data file.
You can also set the '''Angular Resolution''' of the transmitter rays in degrees. By default, every transmitter emanates equi-angular ray tubes at a resolution of 1 degree. Lower angular resolutions larger than 1° speed up the SBR simulation significantly, but they may compromise the accuracy. Higher angular resolutions less than 1° increase the accuracy of the simulating results, but they also increase the computation time. The SBR Engine Settings dialog also shows the required '''Minimum Angular Resolution''' in degrees in a greyed-out box. This number is calculated based on the overall extents of your computational domain as well as the SBR mesh resolution. To see this value, you have to generate the SBR mesh first. Keeping the angular resolution of your project above this threshold value makes sure that the small mesh facets at very large distances from the source would not miss any impinging ray tubes during the simulation.
== Statistical Analysis of Propagation Scene ==