If you look carefully at Figure 21.14, you see that the cylinder has a top but the triangular prism and the box don’t. AutoCAD creates top and bottom surfaces on some objects with thickness but not on others.
Če si pozorno ogledate sliko 21.14, lahko opazite, da ima valj pokrov, trikotna prizma in kvader pa ne. AutoCAD na nekatere predmete z višino postavi pokrov in dno (zgornjo in spodnjo površino), na druge pa ne.