Geo::Ellipsoids(3pm)

1Geo::Ellipsoids(3)    User Contributed Perl Documentation   Geo::Ellipsoids(3)
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NAME

6       Geo::Ellipsoids - Package for standard Geo:: ellipsoid a, b, f and 1/f
7       values.
8

SYNOPSIS

10         use Geo::Ellipsoids;
11         my $obj = Geo::Ellipsoids->new();
12         $obj->set('WGS84'); #default
13         print "a=", $obj->a, "\n";
14         print "b=", $obj->b, "\n";
15         print "f=", $obj->f, "\n";
16         print "i=", $obj->i, "\n";
17         print "e=", $obj->e, "\n";
18         print "n=", $obj->n(45), "\n";
19

DESCRIPTION

CONSTRUCTOR

22       new
23
24       The new() constructor may be called with any parameter that is appro‐
25       priate to the set method.
26
27         my $obj = Geo::Ellipsoid->new();
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METHODS

30       set
31
32       Method sets the current ellipsoid.  This method is called when the
33       object is constructed (default is WGS84).
34
35         $obj->set(); #default WGS84
36         $obj->set('Clarke 1866'); #All built in ellipsoids are stored in meters
37         $obj->set({a=>1, b=>1});  #Custom Sphere 1 unit radius
38
39       list
40
41       Method returns a list of known elipsoid names.
42
43         my @list=$obj->list;
44
45         my $list=$obj->list;
46         while (@$list) {
47           print "$_\n";
48         }
49
50       a
51
52       Method returns the value of the semi-major axis.
53
54         my $a=$obj->a;
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56       b
57
58       Method returns the value of the semi-minor axis.
59
60         my $b=$obj->b;  #b=a(1-f)
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62       f
63
64       Method returns the value of flatting
65
66         my $f=$obj->f;  #f=(a-b)/a
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68       i
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70       Method returns the value of the inverse flatting
71
72         my $i=$obj->i; #i=1/f=a/(a-b)
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74       invf
75
76       Method synonym for the i method
77
78         my $i=$obj->invf; #i=1/f
79
80       e
81
82       Method returns the value of the first eccentricity, e.  This is the
83       eccentricity of the earth's elliptical cross-section.
84
85         my $e=$obj->e;
86
87       e2
88
89       Method returns the value of eccentricity squared (e.g. e^2). This is
90       not the second eccentricity, e' or e-prime see the "ep" method.
91
92         my $e=sqrt($obj->e2); #e^2 = f(2-f) = 2f-f^2 = 1-b^2/a^2
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94       ep
95
96       Method returns the value of the second eccentricity, e' or e-prime.
97       The second eccentricity is related to the first eccentricity by the
98       equation: 1=(1-e^2)(1+e'^2).
99
100         my $ep=$obj->ep;
101
102       ep2
103
104       Method returns the square of value of second eccentricity, e'
105       (e-prime).  This is more useful in almost all equations.
106
107         my $ep=sqrt($obj->ep2);  #ep2=(ea/b)^2=e2/(1-e2)=a^2/b^2-1
108
109       n
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111       Method returns the value of n given latitude (degrees).  Typically rep‐
112       resented by the Greek letter nu, this is the radius of curvature of the
113       ellipsoid perpendicular to the meridian plane.  It is also the distance
114       from the point in question to the polar axis, measured perpendicular to
115       the ellipsoid's surface.
116
117         my $n=$obj->n($lat);
118
119       Note: Some define a variable n as (a-b)/(a+b) this is not that vari‐
120       able.
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122       n_rad
123
124       Method returns the value of n given latitude (radians).
125
126         my $n=$obj->n_rad($lat);
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128       rho
129
130       rho is the radius of curvature of the earth in the meridian plane.
131
132         my $rho=$obj->rho($lat);
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134       rho_rad
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136       rho is the radius of curvature of the earth in the meridian plane.
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138         my $rho=$obj->rho_rad($lat);
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140       polar_circumference
141
142       Method returns the value of the semi-minor axis times 2*PI.
143
144         my $polar_circumference=$obj->polar_circumference;
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146       equatorial_circumference
147
148       Method returns the value of the semi-major axis times 2*PI.
149
150         my $equatorial_circumference=$obj->equatorial_circumference;
151
152       shortname
153
154       Method returns the shortname, which is the hash key, of the current
155       ellipsoid
156
157         my $shortname=$obj->shortname;
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159       longname
160
161       Method returns the long name of the current ellipsoid
162
163         my $longname=$obj->longname;
164
165       data
166
167       Method returns a hash reference for the ellipsoid definition data
168       structure.
169
170         my $datastructure=$obj->data;
171
172       name2ref
173
174       Method returns a hash reference (e.g. {a=>6378137,i=>298.257223563})
175       when passed a valid ellipsoid name (e.g. 'WGS84').
176
177         my $ref=$obj->name2ref('WGS84')
178

TODO

180       What should we do about bad input?  I tend to die in the module which
181       for most situations is fine.  I guess you could always overload die to
182       handle exceptions for web based solutions and the like.
183
184       Support for ellipsoid aliases in the data structure
185

BUGS

187       Please send to the geo-perl email list.
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LIMITS

190       No guarantees that Perl handles all of the double precision calcula‐
191       tions in the same manner as Fortran.
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AUTHOR

194       Michael R. Davis qw/perl michaelrdavis com/
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LICENSE

197       Copyright (c) 2006 Michael R. Davis (mrdvt92)
198
199       This library is free software; you can redistribute it and/or modify it
200       under the same terms as Perl itself.
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