Mapping Toolbox

geoid vector

Define geoid model

Description

The geoid vector is a one- or two-element vector that describes a spheroid approximating the geoid. Its normal form is a two-element vector of the form:

• [semimajor-axis eccentricity]
  

Eccentricity can range from 0 to 1. When only one element is provided, a spherical (0) eccentricity is assumed. When a geoid input is optional, the lack of an input results in a spherical Earth assumption, which is sufficient for most applications. The semimajor axis is entered in terms of some unit of distance measure. While this could be anything, bear in mind that some functions will calculate output based upon the semimajor axis units.

Examples

When used, the default geoid for the Earth is the 1980 Geodetic Reference System ellipsoid:

• almanac('earth','geoid','kilometers')
  ans =
     1.0e+03 *
     6.37813700000000   0.00008181919104
  

Notice how close this is to a spherical geoid definition:

• almanac('earth','sphere','kilometers')
  ans =
          6371           0
  

See Also

almanac

Planetary data

geographic data structure

getm