Hourglass

Snyder's Hourglass projection, using the extended formulas described in [JimenezShaw2026].

Added in version 9.9.0.

Classification	Pseudo cylindrical, equal area
Available forms	Forward and inverse, spherical, ellipsoidal
Defined area	Global
Alias	hourglass
Domain	2D
Input type	Geodetic coordinates
Output type	Projected coordinates

proj-string: +proj=hourglass

Parameters

Note

All parameters are optional.

+lon_0=<value>

Central meridian/longitude of natural origin, longitude of origin or longitude of false origin (naming and meaning depend on the projection method).

Defaults to 0.0.

Note

The default convention is to interpret this value as decimal degrees. To specify radians instead, follow the value with the "r" character.

Example: +lon_0=1.570796r

See Projection Units for more information.

+R=<value>

Radius of the sphere, given in meters. If used in conjunction with +ellps, +R takes precedence.

See Ellipsoid size parameters for more information.

+n=<value>

Exponent applied to the meridians shape. Snyder's image used 1.

Defaults to 1.

+s=<value>

Aspect ratio of the total projection. "Landscape" map has "s" less than 1 Snyder's image used 0.5.

Defaults to 1.

+outinvalid=<value>

Integer value setting the scope of the inverse transformation. A value of 1 plots only the hourglass. Values greater than 1 extend the covered area. 0 covers the entire area.

Defaults to 1.