2 1/2 D objects.Objects are actually one simplest class of objects created sweep . In generalised sweep a 2D area is taken and swept along a path called generator which itself can be a straight line or curve , to create a 3D geometry. There is further generalisation that 2D area itself can vary , also 3D object can be taken for sweep . But for the class of 2 1/2 D objects 2D area of constant cross section and in horizontal ,xy-plane, is swept along straight line perpendicular to area (z-direction ), to create the object. . Example of 2 1/2 D or layered object.

There are different basic approaches in this area.

1. One method is to cut the geometry with sequential layers and machine each identified feature in logical sequence.
2. The other methodology based on extracting the manufacturing details from the from the geometry , then machining of each identified feature in logical sequence. In Feature Recognition there are again different approaches like Hint based reasoning, Convex hull decomposition and Cell based decomposition etc. The problem in this is that many times conflicts arise in the identified features.