<tr>
<td>
[[Image:ART MANH Fig5.png|thumb|left|640px|The location of the transmitter (in blue circle) and the dense receiver grid (yellow points) placed 1.5m above the ground covering the entire scene.]]
</td>
</tr>
</table>
<table><tr><td>[[Image:ART MANH Fig4.png|thumb|left|720px|The mesh view == SBR Analysis of the Manhattan scene.]]</td></tr></table>Â Â Â All the buildings belong to the same group called Block_1, which is of the "Impenetrable Surface" type. The material composition is "Brick" Scene with ε<sub>r</sub> a Vertical Dipole Transmitter = 4.44 and σ = 0.001S/m. In [[EM.Cube]]'s [[Propagation Module]], you can force all the objects belonging to a group to adjust to their underlying terrain. This means that the Z-coordinate of the base of the buildings is elevated to equal the terrain elevation at the building's LCS center coordinates. For that purpose, you have to check the checkbox labeled "Adjust Blocks to Terrain Elevation" is the surface group's property dialog as shown in the opposite figure. Â The source in the Manhattan scene is a vertically polarized short dipole radiator located at (1050m, 1050m, 40m). The scene contains a very large 128 × 116 grid of isotropic receivers spaced 10m apart from one another covering the entire scene. The receivers are placed 2m above the terrain elevation at each point.
Due to the very large size of the propagation scene, we choose an angular resolution of 0.1° for this simulation. This generates a total of 648,000 initial rays that emanate from the transmitter in all directions. The reflected rays are limited to a maximum of 10 bounces. The sensitivity of the receivers is set to -100dBm. This means that if the power of any ray falls below this threshold before reaching a receiver, that ray is terminated in the scene.
<table>
<tr>
<td>
[[Image:PROP250ART MANH Fig4.png|thumb|750pxleft|A perspective 720px|The mesh view of the Manhattan scene showing the receivers and short dipole transmitter.]]
</td>
</tr>
</table>
==A Note on SBR Mesh Generation for Complex Large-Scale Scenes==
[[EM.Cube]]'s Propagation Modules generates a triangular surface mesh for SBR ray tracing analysis. This mesh is similar in nature to the surface triangular meshes used by some of [[EM.Cube]]'s other modules like the Surface MoM and Physical Optics (PO). However, for ray tracing, the goal of mesh generation is to discretize buildings into flat triangular facets. The size of these facets is driven by geometrical fidelity rather than the simulation's operating wavelength. As a result, the mesh density is specified in terms of "Cell Edge Length" in project units rather than in the form of number of cells per wavelength. For this project, set the edge length to 25 units. Although a lot of buildings have dimensions and geometrical details less then 25m, this would be a good choice. Most geometrical details will be captured accurately in the generated mesh, while you will also avoid creating too many coplanar facets on the flat sides of the larger rectangular buildings.
Generate and view the mesh of the Manhattan scene and see how [[EM.Cube]] combines multi-object buildings together to create a consistent mesh. In fact, connected or overlapped objects undergo a Boolean union operation before being discretized by the mesh generator.
{{Note|In [[EM.Cube]]'s [[Propagation Module]], the mesh of the terrain is not explicitly displayed because a terrain object is either created or imported as a tessellated surface object, which is already a discretized object.}}
Â
<table>
<tr>
<td>
[[Image:PROP251.png|thumb|900px|Buildings of Impenetrable Surface type on the global ground in the Ann Arbor scene propagation scene.]]
</td>
</tr>
</table>
Â
There are numerous cases that mesh generation for complex large-scale scene may fail in the first attempt. Most of such cases stem from [[EM.Cube]]'s failure to perform the Boolean union operation on complex overlapping objects. When your scene contains hundreds or thousands of such objects, the odds of failure would naturally rise. If you look at the list of the building in the Navigation Tree, you will notice that all of the objects except for the last one are of "Generic Solid" type. The last object is a "Boolean" object. When we first imported the Manhattan buildings from external CAD files to build this project, there were initially a total of 622 [[Solid Objects|solid objects]]. The mesh generator failed to union the constituents of the bright-yellow-highlighted building shown in the figure below. This building originally consisted of 8 individual [[Solid Objects|solid objects]], that were indexed from Solid_543 to Solid_550. We divided these objects into groups of 2 or 3 and performed Boolean union operation on each group separately. If Boolean union operations are completed successfully, the mesh will be generated without failure. Finally, we combined the resulting Boolean objects into a single Boolean object called "Boolean_623". You can see from the Navigation Tree that the index range 543-550 is missing from the solids' list for this very reason.
Â
<table>
<tr>
<td>
[[Image:PROP265.png|thumb|500px|The (highlighted) building of the Boolean type in the Manhattan scene.]]
</td>
<td>
[[Image:PROP266.png|thumb|500px|The surface triangular mesh of the Boolean building in the Manhattan scene.]]
</td>
</tr>
</table>
Â
[[Image:PROP253.png|thumb|550px|The received power coverage map of the Manhattan scene with the transmitter located 40m above the ground in the upper right part of the scene.]]
==Running an SBR Analysis of the Manhattan Scene==
Run an SBR analysis of the project's scene and visualize the received power coverage map as shown the opposite figure. Keep in mind that the mesh generation may take a fairly long amount of time. Have patience and let [[EM.Cube]] finish its job. From the figure you can see that the wireless coverage barley penetrates into the streets due to the dense configuration of impenetrable buildings.