ISO 10303-523:2004 specifies the interpretation of the integrated resources to satisfy the requirement for the definition of a shape representation containing implicitly defined solids created by sweeping operations. The solids are defined by sweeping a planar area along a directrix curve. For the surface_curve_swept_area_solid both the area and directrix are explicitly defined. For other types of swept_area_solid the directrix is implicitly defined, as a line or a circle. In the case of the swept_disk_solid, the bounds of the area are implicitly defined circles.