## Documentation |

Central Meridian: Straight line (includes meridian opposite the central meridian in one continuous line).

Other Meridians: Straight lines if 90º from central meridian, complex curves concave toward the central meridian otherwise.

Parallels: Complex curves concave toward the nearest pole.

Poles: Points along the central meridian.

Symmetry: About any straight meridian or the Equator.

This is a projection onto a cylinder tangent at the central meridian. Distortion of both shape and area are functions of distance from the central meridian. Scale is true along the central meridian and along any straight line perpendicular to the central meridian (i.e., it is equidistant).

For cylindrical projections, only one standard parallel is specified.
The other standard parallel is the same latitude with the opposite
sign. For this projection, the standard parallel *of the
base projection* is by definition fixed at 0º.

This projection is the transverse aspect of the Plate Carrée projection, developed by César François Cassini de Thury (1714–1784). It is still used for the topographic mapping of a few countries.

`cassinistd` implements the Cassini projection
directly on a sphere or reference ellipsoid, as opposed to using
the equidistant cylindrical projection in transverse mode as in function `cassini`.
Distinct forms are used for the sphere and ellipsoid, because approximations
in the ellipsoidal formulation cause it to be appropriate only within
a zone that extends 3 or 4 degrees in longitude on either side of
the central meridian.

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