This is the summary of the surface decomposition.
As we see, slant triangles on Cone A …
Shown on the left is another example, where blue, yellow, and white flat triangles indicate the area of “In”, “Boundary”, and “Out.”
Shown on the right is a schematic diagram of the relative position of slant triangles and the conjugate roof. Slant triangles belong to “In” until the top vertex crosses the surface of the conjugate roof. Then, it belongs to “Boundary”. All the triangles above the “Boundary” triangle belong to “Out.”