Icosahedral Snyder Equal Area

Snyder's Icosahedral Equal Area map projections on polyhedral globes for the dodecahedron and truncated icosahedron offer relatively low scale and angular distortion. The equations involved are relatively straight-forward, and for certain instructional tools and databases, the projections are useful for world maps. The interruptions remain a disadvantage, as with any low-error projection system applied to the entire globe [Snyder1992].

Classification	Polyhedral, equal area
Available forms	Forward, spherical
Defined area	Global
Alias	isea
Domain	2D
Input type	Geodetic coordinates
Output type	Projected coordinates

proj-string: +proj=isea

Parameters

Note

All parameters are optional for the projection.

+orient=<string>

Can be set to either isea or pole. See Snyder's Figure 12 for pole orientation [Snyder1992].

Defaults to isea

+azi=<value>

Azimuth.

Defaults to 0.0

+aperture=<value>

Defaults to 3.0

+resolution=<value>

Defaults to 4.0

+mode=<string>

Can be either plane, di, dd or hex.

Defaults to plane

+lon_0=<value>

Longitude of projection center.

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.

+lat_0=<value>

Latitude of projection center.

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: +lat_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.

+x_0=<value>

False easting.

Defaults to 0.0.

+y_0=<value>

False northing.

Defaults to 0.0.