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# NAME
Geo::Ellipsoids - Package for standard Geo:: ellipsoid a, b, f and 1/f values.
# SYNOPSIS
use Geo::Ellipsoids;
my $obj = Geo::Ellipsoids->new();
$obj->set('WGS84'); #default
print "a=", $obj->a, "\n";
print "b=", $obj->b, "\n";
print "f=", $obj->f, "\n";
print "i=", $obj->i, "\n";
print "e=", $obj->e, "\n";
print "n=", $obj->n(45), "\n";
# DESCRIPTION
Package for standard Geo:: ellipsoid a, b, f and 1/f values.
# CONSTRUCTOR
## new
The new() constructor may be called with any parameter that is appropriate to the set method.
my $obj = Geo::Ellipsoid->new();
# METHODS
## initialize
## 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
$obj->set({a=>1, b=>1}); #Custom Sphere 1 unit radius
## list
Method returns a list of known ellipsoid names.
my @list=$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 $e2 = sqrt($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_rad = $obj->n_rad($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')
# AUTHOR
Michael R. Davis
# LICENSE
Copyright (c) 2006 Michael R. Davis
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
# SEE ALSO
[Geo::Forward](https://metacpan.org/pod/Geo::Forward), [Geo::Ellipsoid](https://metacpan.org/pod/Geo::Ellipsoid), [Geo::Coordinates::UTM](https://metacpan.org/pod/Geo::Coordinates::UTM), [Geo::GPS::Data::Ellipsoid](https://metacpan.org/pod/Geo::GPS::Data::Ellipsoid), [GIS::Distance](https://metacpan.org/pod/GIS::Distance)
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