new¶

The new() constructor may be called with any parameter that is appropriate to the set method.

  my $obj = Geo::Ellipsoid->new();

set¶

Method sets the current ellipsoid. This method is called when the object is constructed (default is WGS84).

  $obj->set(); #default WGS84
  $obj->set('Clarke 1866'); #All built in ellipsoids are stored in meters
  $obj->set({a=>1, b=>1});  #Custom Sphere 1 unit radius

list¶

Method returns a list of known elipsoid names.

  my @list=$obj->list;
  my $list=$obj->list;
  while (@$list) {
    print "$_\n";
  }

a¶

Method returns the value of the semi-major axis.

  my $a=$obj->a;

b¶

Method returns the value of the semi-minor axis.

  my $b=$obj->b;  #b=a(1-f)

f¶

Method returns the value of flatting

  my $f=$obj->f;  #f=(a-b)/a

i¶

Method returns the value of the inverse flatting

  my $i=$obj->i; #i=1/f=a/(a-b)

invf¶

Method synonym for the i method

  my $i=$obj->invf; #i=1/f

e¶

Method returns the value of the first eccentricity, e. This is the eccentricity of the earth's elliptical cross-section.

  my $e=$obj->e;

e2¶

Method returns the value of eccentricity squared (e.g. e^2). This is not the second eccentricity, e' or e-prime see the "ep" method.

  my $e=sqrt($obj->e2); #e^2 = f(2-f) = 2f-f^2 = 1-b^2/a^2

ep¶

Method returns the value of the second eccentricity, e' or e-prime. The second eccentricity is related to the first eccentricity by the equation: 1=(1-e^2)(1+e'^2).

  my $ep=$obj->ep;

ep2¶

Method returns the square of value of second eccentricity, e' (e-prime). This is more useful in almost all equations.

  my $ep=sqrt($obj->ep2);  #ep2=(ea/b)^2=e2/(1-e2)=a^2/b^2-1

n¶

Method returns the value of n given latitude (degrees). Typically represented by the Greek letter nu, this is the radius of curvature of the ellipsoid perpendicular to the meridian plane. It is also the distance from the point in question to the polar axis, measured perpendicular to the ellipsoid's surface.

  my $n=$obj->n($lat);

Note: Some define a variable n as (a-b)/(a+b) this is not that variable.

Note: It appears that n can also be calculated as

  n=a^2/sqrt(a^2 * cos($lat)^2 + $b^2 * sin($lat)^2);

n_rad¶

Method returns the value of n given latitude (radians).

  my $n=$obj->n_rad($lat);

Reference: John P. Snyder, "Map Projections: A Working Manual", USGS, page 25, equation (4-20) http://pubs.er.usgs.gov/usgspubs/pp/pp1395

rho¶

rho is the radius of curvature of the earth in the meridian plane.

  my $rho=$obj->rho($lat);

rho_rad¶

rho is the radius of curvature of the earth in the meridian plane. Sometimes denoted as R'.

  my $rho=$obj->rho_rad($lat);

Reference: John P. Snyder, "Map Projections: A Working Manual", USGS, page 24, equation (4-18) http://pubs.er.usgs.gov/usgspubs/pp/pp1395

polar_circumference¶

Method returns the value of the semi-minor axis times 2*PI.

  my $polar_circumference=$obj->polar_circumference;

equatorial_circumference¶

Method returns the value of the semi-major axis times 2*PI.

  my $equatorial_circumference=$obj->equatorial_circumference;

shortname¶

Method returns the shortname, which is the hash key, of the current ellipsoid

  my $shortname=$obj->shortname;

longname¶

Method returns the long name of the current ellipsoid

  my $longname=$obj->longname;

data¶

Method returns a hash reference for the ellipsoid definition data structure.

  my $datastructure=$obj->data;

name2ref¶

Method returns a hash reference (e.g. {a=>6378137,i=>298.257223563}) when passed a valid ellipsoid name (e.g. 'WGS84').

  my $ref=$obj->name2ref('WGS84')