CN Card

On the Construct tab, in the Modify group, click the  Reverse normals (CN) icon.

Figure 1. The CN - Reverse triangle and polygon normals dialog.

Parameters:

Reverse normal of selected

In this group, the user selects to reverse the normals of either Triangles or Polygons.

Selection by

Here, the user specifies whether the triangles or polygonal plates are identified by their Label or absolute element Number.

Selection

The label or element number of the triangles or polygonal plates that are to have their normals reversed.

The normal direction can be important, such as when defining dielectric surfaces. For triangles, the normal vector is reversed by interchanging corners 1 and 3. For polygonal plates, the first point remains as is but the corner points are listed in the opposite direction.

The CN card changes the normal of the affected triangles but it does not change the settings of the ME card (which medium is on which side of the triangle is determined by the normal vector). For example, if the ME card is used to specify that the normal vectors of the triangles point from medium 5 to medium 2 then the application of the CN card will effectively change which medium lies on which physical side of the triangle.