+
+ +
+

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.

+
+ +
+
++lat_0=<value>
+

Latitude of projection center.

+

Defaults to 0.0.

+
+ +
+
++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.

+
+ +
+
+ + +
+