zenithal

All round the horizon is built a black cloud-wall, but the zenithal heaven is clear.

It is clear that perspective and zenithal projections are particular groups of conical projections.

This gives either the group of conical projections with rectified meridians, or as a particular case the equidistant zenithal.

Of the above 25 projections, 23 are conical or quasi-conical, if zenithal and perspective projections be included.

It is obvious that all perspective projections are zenithal.