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.
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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";
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DESCRIPTION

CONSTRUCTOR

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

29   set
30       Method sets the current ellipsoid.  This method is called when the
31       object is constructed (default is WGS84).
32
33         $obj->set(); #default WGS84
34         $obj->set('Clarke 1866'); #All built in ellipsoids are stored in meters
35         $obj->set({a=>1, b=>1});  #Custom Sphere 1 unit radius
36
37   list
38       Method returns a list of known elipsoid names.
39
40         my @list=$obj->list;
41
42         my $list=$obj->list;
43         while (@$list) {
44           print "$_\n";
45         }
46
47   a
48       Method returns the value of the semi-major axis.
49
50         my $a=$obj->a;
51
52   b
53       Method returns the value of the semi-minor axis.
54
55         my $b=$obj->b;  #b=a(1-f)
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57   f
58       Method returns the value of flatting
59
60         my $f=$obj->f;  #f=(a-b)/a
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62   i
63       Method returns the value of the inverse flatting
64
65         my $i=$obj->i; #i=1/f=a/(a-b)
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67   invf
68       Method synonym for the i method
69
70         my $i=$obj->invf; #i=1/f
71
72   e
73       Method returns the value of the first eccentricity, e.  This is the
74       eccentricity of the earth's elliptical cross-section.
75
76         my $e=$obj->e;
77
78   e2
79       Method returns the value of eccentricity squared (e.g. e^2). This is
80       not the second eccentricity, e' or e-prime see the "ep" method.
81
82         my $e=sqrt($obj->e2); #e^2 = f(2-f) = 2f-f^2 = 1-b^2/a^2
83
84   ep
85       Method returns the value of the second eccentricity, e' or e-prime.
86       The second eccentricity is related to the first eccentricity by the
87       equation: 1=(1-e^2)(1+e'^2).
88
89         my $ep=$obj->ep;
90
91   ep2
92       Method returns the square of value of second eccentricity, e'
93       (e-prime).  This is more useful in almost all equations.
94
95         my $ep=sqrt($obj->ep2);  #ep2=(ea/b)^2=e2/(1-e2)=a^2/b^2-1
96
97   n
98       Method returns the value of n given latitude (degrees).  Typically
99       represented by the Greek letter nu, this is the radius of curvature of
100       the ellipsoid perpendicular to the meridian plane.  It is also the
101       distance from the point in question to the polar axis, measured
102       perpendicular to the ellipsoid's surface.
103
104         my $n=$obj->n($lat);
105
106       Note: Some define a variable n as (a-b)/(a+b) this is not that
107       variable.
108
109       Note: It appears that n can also be calculated as
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111         n=a^2/sqrt(a^2 * cos($lat)^2 + $b^2 * sin($lat)^2);
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113   n_rad
114       Method returns the value of n given latitude (radians).
115
116         my $n=$obj->n_rad($lat);
117
118       Reference: John P. Snyder, "Map Projections: A Working Manual", USGS,
119       page 25, equation (4-20) http://pubs.er.usgs.gov/usgspubs/pp/pp1395
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121   rho
122       rho is the radius of curvature of the earth in the meridian plane.
123
124         my $rho=$obj->rho($lat);
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126   rho_rad
127       rho is the radius of curvature of the earth in the meridian plane.
128       Sometimes denoted as R'.
129
130         my $rho=$obj->rho_rad($lat);
131
132       Reference: John P. Snyder, "Map Projections: A Working Manual", USGS,
133       page 24, equation (4-18) http://pubs.er.usgs.gov/usgspubs/pp/pp1395
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135   polar_circumference
136       Method returns the value of the semi-minor axis times 2*PI.
137
138         my $polar_circumference=$obj->polar_circumference;
139
140   equatorial_circumference
141       Method returns the value of the semi-major axis times 2*PI.
142
143         my $equatorial_circumference=$obj->equatorial_circumference;
144
145   shortname
146       Method returns the shortname, which is the hash key, of the current
147       ellipsoid
148
149         my $shortname=$obj->shortname;
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151   longname
152       Method returns the long name of the current ellipsoid
153
154         my $longname=$obj->longname;
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156   data
157       Method returns a hash reference for the ellipsoid definition data
158       structure.
159
160         my $datastructure=$obj->data;
161
162   name2ref
163       Method returns a hash reference (e.g. {a=>6378137,i=>298.257223563})
164       when passed a valid ellipsoid name (e.g. 'WGS84').
165
166         my $ref=$obj->name2ref('WGS84')
167

TODO

169       What should we do about bad input?  I tend to die in the module which
170       for most situations is fine.  I guess you could always overload die to
171       handle exceptions for web based solutions and the like.
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173       Support for ellipsoid aliases in the data structure
174

BUGS

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

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

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

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