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

Icosahedral Snyder Equal Area

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=1.5708r

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=1.5708r

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.