Define a geometric region from the set of surfaces by logically combining the surface names. A region may be removed from the geometry by specifying the release keyword.
To define a region, the operators lt, le, gt, and ge are applied to previously defined surfaces according to the following rules.
lt – if the surface following is a volume then lt means inside not including the surface of the volume. If the surface is a plane or a sheet lt means the space on the side of the plane or sheet opposite to the normal not including the plane or sheet itself.
le – if the surface following is a volume then le means inside including the surface of the volume. If the surface is a plane or a sheet le means the space on the side of the plane or sheet opposite to the normal including the plane or sheet itself.
gt – if the surface following is a volume then gt means outside not including the surface of the volume. If the surface is a plane or a sheet gt means the space on the same side of the plane or sheet as the normal not including the plane or sheet itself.
ge – if the surface following is a volume then ge means outside including the surface of the volume. If the surface is a plane or a sheet ge means the space on the same side of the plane or sheet as the normal including the plane or sheet itself.
The operators or, and, and not applied to surfaces mean union, intersection and complement respectively. The parentheses operators, (and ), are used for nesting. Spaces are required as delimiters to separate all operators and operands. Internal interfaces should be included in exactly one region. In the event of conflicting region commands, the one occurring last in the input stream takes precedence. Defining a region will cause the information associated with this material region to be stored under the name of the geometry of the current mesh object. Releasing the region will remove this information.