EM.Illumina can only handle surface and solid CAD objects. Only the outer surface of [[Solid Objects|solid objects]] is considered in the PO simulation. No line or [[Curve Objects|curve objects]] are allowed in the project workspace; or else, they will be ignored during the PO simulation. You can define several PEC, PMC or impedance surface groups with different colors and impedance values. All the objects created and drawn under a group share the same color and other properties.
A new surface group can be defined by simply right clicking on one of the three '''PEC''', '''PMC''' or '''Impedance Surface''' items in the '''Physical Structure''' section of the navigation tree and selecting '''Insert New PEC..[[Image:Info_icon.png|40px]] Click here to learn more about ''', '''Insert New PMC[[Defining_Materials_in_EM...''', or '''Insert Cube#Defining_a_New_Material_Group | Defining a New Impedance Surface...''' from the contextual menu. A dialog for setting up the group properties opens up. In this dialog you can change the name of the group or its color. In the case of a surface impedance group, you can set the values for the real and imaginary parts of the '''Surface ImpedanceMaterial Group]]''' in Ohms.
<table><tr><td> [[Image:PO19Once a new material node has been created on the navigation tree, it becomes the "Active" material group of the project workspace, which is always listed in bold letters.png|thumb|280px|The PEC dialogWhen you draw a new CAD object such as a Box or a Sphere, it is inserted under the currently active material type.]] </td><td> [[Image:PO20There is only one material group that is active at any time.png|thumb|280px|The PMC dialogAny material can be made active by right clicking on its name in the Navigation Tree and selecting the '''Activate''' item of the contextual menu.]] </td><td> It is recommended that you first create material groups, and then draw new objects under the active material group. However, if you start a new [[Image:PO21.png|thumb|280px|The Impedance Surface dialogEM.Tempo]] </td></tr></table>Â === Creating New Objects & Moving Them Around ===project from scratch, and start drawing a new object without having previously defined any material groups, a new default PEC group is created and added to the navigation tree to hold your new CAD object.
[[Image:PO22(1).png|thumb|400px|Moving objects among different surface groups in EM.Illumina.]]
The objects that you draw in [[EM.Cube]]'s project workspace always belong to the "Active" surface group. By default, the last object group that you created remains active until you change it. The current active group is always listed in bold letters in the Navigation Tree. Any surface group can be made active by right clicking on its name in the Navigation Tree and selecting the '''Activate''' item of the contextual menu. If you start a new EM.Illumina project and draw any object without having previously defined a surface group, a default PEC group is automatically created and added to the Navigation Tree to hold your new object.
You can move one or [[Image:Info_icon.png|40px]] Click here to learn more selected objects to any material group. Right click on the highlighted selection and select about '''Move To > Physical Optics >[[Defining_Materials_in_EM.Cube#Moving_Objects_among_Material_Groups | Moving Objects among Material Groups]]''' from the contextual menu. This opens another sub-menu with a list of all the available surface groups already defined in  {{Note|In [[EM.Illumina. Select the desired surface groupCube]], and all the selected objects will move to that group. The objects you can be selected either in the project workspaceimport external CAD models (such as STEP, or their names can be selected from the Navigation Tree. In the latter caseIGES, make sure that you hold the keyboard's '''Shift Key''' or '''Ctrl Key''' down while selecting a material group's name from the contextual menuSTL models, etc. You can also move one or more objects from a PO surface group ) only to [[EM.CubeCubeCAD]]'s other modules, or vice versa. In that case, the sub-From [[menusCubeCAD]] of , you can then move the '''Move To >''' item of the contextual menu will indicate all the [[imported objects to EM.Cube]] modules that have valid groups for transfer of the selected objectsIllumina. }}
{{Note|In [[EMImage:Info_icon.Cubepng|40px]], you can import external CAD models (such as STEP, IGES, STL models, etc.) only to Click here for a general discussion of '''[[CubeCAD]]Defining Materials in EM. From [[CubeCAD]], you can then move the imported objects to any other computational module including [[PO ModuleCube]]'''.}}
== Discretizing the Physical Structure ==