Geometric shapes of models of accretion disks. (I) Denotes the slab, (II) the wedge, (III) the lens, and (IV) the envelope. The latter is shown as if it was filling the Roche limit, that is R_out = R_L1, where R_out = R_L1 denotes point radius of the Roche lobe. Here it is shown this way to emphasize the geometry of the disk, but its shape may be more symmetric depending on its filling factor. See Sect. 4.3 for the description of individual disk shapes. The Nebula is not presented here, since no simple geometrical sketch can be given. It is illustrated, however, in Fig. 5.