An isoline is used to give a visual clue to the shape of an object. The AcGiWorldDraw::isolines() function allows an entity to display the same number of isolines per surface as specified by the user. This value is an integer between 0 and 2047. The default number of isolines is 4. The AcGiViewportDraw class provides an analogous function:
virtual Adesk::UInt32 AcGiWorldDraw::numberOfIsolines() const;