Provided by: libgeo-ellipsoids-perl_0.16-1_all

**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**

newThenew()constructor may be called with any parameter that is appropriate to the set method. my $obj = Geo::Ellipsoid->new();

**METHODS**

setMethod 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 $obj->set({a=>1, b=>1}); #Custom Sphere 1 unit radiuslistMethod returns a list of known elipsoid names. my @list=$obj->list; my $list=$obj->list; while (@$list) { print "$_\n"; }aMethod returns the value of the semi-major axis. my $a=$obj->a;bMethod returns the value of the semi-minor axis. my $b=$obj->b; #b=a(1-f)fMethod returns the value of flatting my $f=$obj->f; #f=(a-b)/aiMethod returns the value of the inverse flatting my $i=$obj->i; #i=1/f=a/(a-b)invfMethod synonym for the i method my $i=$obj->invf; #i=1/feMethod returns the value of the first eccentricity, e. This is the eccentricity of the earth's elliptical cross-section. my $e=$obj->e;e2Method 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^2epMethod 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;ep2Method 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^2-1nMethod 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_radMethod 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/pp1395rhorho is the radius of curvature of the earth in the meridian plane. my $rho=$obj->rho($lat);rho_radrho 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/pp1395polar_circumferenceMethod returns the value of the semi-minor axis times 2*PI. my $polar_circumference=$obj->polar_circumference;equatorial_circumferenceMethod returns the value of the semi-major axis times 2*PI. my $equatorial_circumference=$obj->equatorial_circumference;shortnameMethod returns the shortname, which is the hash key, of the current ellipsoid my $shortname=$obj->shortname;longnameMethod returns the long name of the current ellipsoid my $longname=$obj->longname;dataMethod returns a hash reference for the ellipsoid definition data structure. my $datastructure=$obj->data;name2refMethod 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