You can tell FeatureCAM to rough your part as a 3D Pocket, or as a 3D Boss. If you select 3D Pocket, the tool plunges or ramps onto the part and cuts from the inside of the part out toward the boundary of the part. A 3D Boss typically plunges off the part and cuts from the outside toward the center.
Even if the surfaces of your part create a boss shape (meaning it protrudes instead of being a cavity), you can still select 3D Pocket. The first image below shows the slices of a part being cut as a boss, and the second as a pocket. Notice that the slides of the boss go all the way around the part at each slice, but the pocket example has slices that just cut a region of the part.
