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

CONSTRUCTOR

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

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

METHODS

   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')

TODO

       What should we do about bad input?  I tend to die in the module which for most situations
       is fine.  I guess you could always overload die to handle exceptions for web based
       solutions and the like.

       Support for ellipsoid aliases in the data structure

BUGS

       Please send to the geo-perl email list.

LIMITS

       No guarantees that Perl handles all of the double precision calculations in the same
       manner as Fortran.

AUTHOR

       Michael R. Davis qw/perl michaelrdavis com/

LICENSE

       Copyright (c) 2006 Michael R. Davis (mrdvt92)

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

SEE ALSO

       Geo::Forward Geo::Ellipsoid Geo::Coordinates::UTM Geo::GPS::Data::Ellipsoid GIS::Distance