{{twoimg|FDTD34.png|A human head model and a cellular phone handset on its side.|FDTD33.png|The regular FDTD mesh of the human head model and the cellular phone handset.}}
===Mesh Profiling & Grid Coordinate System=== A volumetric FDTD mesh is overwhelming for visualization in Changing the 3D space. For this reason, [[EM.Cube]]'s mesh view only shows the outline of the (staircased) meshed objects, skipping the outline of all the individual brick cells in the entire computational domain. The mesh grid planes provide a 2D profile of the mesh cells along the principal coordinate planes. Since the Yee cells are congruent along the coordinate axes, the three mesh grid planes together provide a complete picture of the entire FDTD mesh. To display a mesh grid planes, select '''Menu > Simulate > Discretization > Grid Planes >''' and pick one of the three options: '''XY Plane''', '''YZ Plane''' or '''ZX Plane'''. You may also right click on one of the '''XY Plane''', '''YZ Plane''' or '''ZX Plane''' items in the '''Discretization''' section of the Navigation Tree and select '''Show''' from the contextual menu. While a mesh grid plane is visible, you can move it back and forth between the two boundary planes at the two opposite sides of the computational domain. You can do this in one of the following four ways: * Using the keyboard's '''Page Up (PgUp) Key''' and '''Page Down (PgDn) key'''.* By selecting '''Menu > Simulate > Discretization > Grid Planes > Increment Grid''' or ''' Decrement Grid'''.* By right clicking on one of the '''XY Plane''', '''YZ Plane''' or '''ZX Plane''' items in the '''Discretization''' section of the Navigation Tree and selecting '''Increment Grid''' or ''' Decrement Grid''' from the contextual menu.* Using the [[Keyboard Shortcuts|keyboard shortcuts]] '''">"''' or '''"<"'''. As you âstep throughâ or profile the mesh grid, you can see how the structure is discretized along internal planes of the computational domain. Once the project structure is meshed in [[EM.Cube]]'s [[FDTD Module]], a second coordinate system becomes available to you. The mesh grid coordinate system allows you to specify any location in the computational domain in terms of node indices on the mesh grid. [[EM.Cube]] displays the total number of mesh grid lines of an FDTD simulation domain (N<sub>x</sub> à N<sub>y</sub> à N<sub>z</sub>) along the three principal axes on the '''Status Bar'''. Therefore, the number of cells in each direction is one less than the number of grid lines, i.e. (N<sub>x</sub>-1)à (N<sub>y</sub>-1) à (N<sub>z</sub>-1). The minimum X, Y, and Z coordinates of the FDTD domain in the world coordinate system (Xmin, Ymin, Zmin), which represent the lower left front corner of the domain box, become the origin of the mesh grid coordinate system (0,0,0), The maximum domain coordinates, which represent the upper right back corner of the domain box, are therefore (N<sub>x</sub>-1, N<sub>y</sub>-1, N<sub>z</sub>-1). [[EM.Cube]] allows you to navigate through the mesh grid and evaluate the grid points individually. Every time you display one of the three mesh grid planes, the "'''Grid Coordinate System (GCS)'''" is automatically activated. On the Status Bar, you will see [[Image:statusgrid.png]] instead of the default [[Image:statusworld.png]]. This means that the current coordinates reported on Status Bar are now expressed in grid coordinate system. The current grid point is displayed by a small white circle on the current mesh grid plane, and it always starts from (I= 0, J=0, K=0). Using the keyboard's '''Arrow Keys''', you can move the white circle through the mesh grid plane and read the current node's (I, J, K) indices on the status bar. You can switch back to the "'''World Coordinate System (WCS)'''" or change to the "'''Domain Coordinate System'''" by double-clicking the status bar box that shows the current coordinate system and cycling through the three options. The domain coordinate system is one that establishes its origin at the lower left front corner of the computational domain and measure distances in project unit just like the WCS. {{isoimg|FDTD35(1).png|The grid cursor on the XY grid plane and its grid coordinates (I, J, K) displayed on the status bar.}} === FDTD Mesh Settings ===
[[Image:FDTD80.png|thumb|400px|[[FDTD Module]]'s Mesh Settings dialog]]
Occasionally, you may prefer a more regular FDTD mesh with almost equal grid line spacing everywhere, but still with a frequency-dependent cell size. In that case, you can select the "<u>'''Regular'''</u>" option of the '''Mesh Type '''dropdown list in the FDTD Mesh Settings dialog. The regular FDTD mesh enforces only two of the above [[parameters]]: '''Minimum Mesh Density''' and '''Absolute Minimum Grid Spacing'''. Or you may opt for an absolutely "<u>'''Uniform'''</u>" mesh type, for which you need to specify the '''Cell Size '''along the X, Y, Z directions in project units.
===Global vs. Local Control Of FDTD Mesh===Â {{mainpage|Click here to learn more about [[[Advanced Meshing in EM.Tempo]]}} Â When [[EM.Cube]] generates an FDTD mesh, a large number of geometrical considerations are taken into account. These include the bounding box of each object and its corners, the ends of a line, the apex of a cone or pyramid, or the locations of lumped sources, field probes and sensors, vertices of plane wave or far field boxes, to name a few examples. These points are âlockedâ as fixed grid nodes in the FDTD mesh. Â You can control the global mesh more selectively using the Advanced FDTD Mesh Settings Dialog. To open this dialog, click the '''Advanced '''button at the bottom of the FDTD Mesh Settings dialog. For example, you can control the quality of the gradual grid transitions by setting the value of '''Max Adjacent Cell Size Ratio'''. Â In certain cases, you may wish to exert some level of local mesh control. For example, you may want to increase the mesh density at a very particular area of your structure. Or you may want to increase or decrease the mesh resolution inside certain types of materials independent of their permittivity and permeability. [[EM.Cube]] provides two additional mechanisms for local control of the FDTD mesh: locking mesh of object groups and user defined fixed grid points.