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3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
4  <head>
5    <title>ll_narcs_distances.pro (SAXO Documentation Assistant)</title>
6  </head>
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55
56
57    <h1><font size="-2">Interpolation/</font></h1>
58    <h2>ll_narcs_distances.pro</h2>
59
60    <dl>
61    </dl>
62
63   
64 This function returns the longitude and latitude [lon, lat] of
65 a point a given arc distance (-pi <= Arc_Dist <= pi), and azimuth (Az),
66 from a specified location Lon0, Lat0.
67 Same as <a href="/Applications/itt/idl64/help/online_help/LL_ARC_DISTANCE.html">LL_ARC_DISTANCE</a> but for n points without do loop.
68
69 Formula from Map Projections - a working manual.  USGS paper
70 1395. Equations (5-5) and (5-6).
71
72
73   
74
75     
76      <a name="#_ll_narcs_distances"></a>
77
78      <h2>ll_narcs_distances  <font size="-1" color="#006633">
79 Mapping, geography
80</font></h2>
81
82      <p><font face="Courier"><i>result = </i>ll_narcs_distances(<i><a href="#_ll_narcs_distances_keyword_lon0">lon0</a>, <a href="#_ll_narcs_distances_keyword_lat0">lat0</a>, <a href="#_ll_narcs_distances_keyword_arc_dist">arc_dist</a>, <a href="#_ll_narcs_distances_keyword_az">az</a></i>, <a href="#_ll_narcs_distances_keyword_DEGREES">DEGREES</a>=<i>DEGREES</i>)</font></p>
83
84   
85
86
87    <h3>Return value</h3>
88 a (2,n) array containing the longitude/latitude of the resulting points.
89 Values are in radians unless the keyword DEGREES is set.
90
91
92   
93    <h3>Parameters</h3>
94   
95
96    <a name="#_ll_narcs_distances_keyword_lon0"></a>
97    <h4>lon0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
98      <font size="-1" color="#006633">in</font>
99     
100     
101      <font size="-1" color="#006633">required</font>
102     
103     
104     
105     
106    </h4>
107
108   
109 An array containing the longitude of the starting point.
110 Values are assumed to be in radians unless the keyword DEGREES is set.
111
112   
113
114    <a name="#_ll_narcs_distances_keyword_lat0"></a>
115    <h4>lat0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
116      <font size="-1" color="#006633">in</font>
117     
118     
119      <font size="-1" color="#006633">required</font>
120     
121     
122     
123     
124    </h4>
125
126   
127 An array containing the latitude of the starting point.
128 Values are assumed to be in radians unless the keyword DEGREES is set.
129
130   
131
132    <a name="#_ll_narcs_distances_keyword_arc_dist"></a>
133    <h4>arc_dist&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
134      <font size="-1" color="#006633">in</font>
135     
136     
137      <font size="-1" color="#006633">required</font>
138     
139     
140     
141     
142    </h4>
143
144   
145 The arc distance from Lon_lat0. The value must be between
146 -!PI and +!PI. To express distances in arc units, divide
147  by the radius of the globe expressed in the original units.
148  For example, if the radius of the earth is 6371 km, divide
149  the distance in km by 6371 to obtain the arc distance.
150
151   
152
153    <a name="#_ll_narcs_distances_keyword_az"></a>
154    <h4>az&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
155      <font size="-1" color="#006633">in</font>
156     
157     
158      <font size="-1" color="#006633">required</font>
159     
160     
161     
162     
163    </h4>
164
165   
166 The azimuth from Lon_lat0. The value is assumed to be in
167 radians unless the keyword DEGREES is set.
168
169   
170   
171
172   
173    <h3>Keywords</h3>
174
175   
176    <a name="#_ll_narcs_distances_keyword_DEGREES"></a>
177    <h4>DEGREES&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
178     
179     
180     
181     
182     
183     
184     
185     
186    </h4>
187
188   
189 Set this keyword to express all measurements and results in degrees.
190
191   
192   
193
194    <h3>Examples</h3><pre>
195 IDL> Lon_lat0 = [1.0, 2.0]; Initial point specified in radians
196 IDL> Arc_Dist = 2.0; Arc distance in radians
197 IDL> Az = 1.0; Azimuth in radians
198 IDL> Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az)
199 IDL> PRINT, Result
200       2.91415    -0.622234
201
202 IDL> lon0 = [-10, 20, 100]
203 IDL> lat0 = [0, -10, 45]
204 IDL> lon1 = [10, 60, 280]
205 IDL> lat1 = [0, 10, 45]
206 IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two)
207 IDL> earthradius = 6378206.4d0
208 IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees)
209 IDL> print, reform(res[0, *])
210       10.000000       60.000000       280.00000
211 IDL> print, reform(res[1, *])
212           1.1999280e-15       10.000000       45.000000
213
214    </pre><h3>Version history</h3>
215   
216    <h4>Version</h4>
217 $Id: ll_narcs_distances.pro 327 2007-12-13 16:22:35Z pinsard $
218
219    <h4>History</h4>
220       Based on the IDL function ll_arc_distance.pro,v 1.11 2003/02/03
221 Sebastien Masson (smasson@lodyc.jussieu.fr)
222                  August 2005
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240    <font size="-3"><p>&nbsp;</p></font>
241    <hr size="1" color="#CCCCCC"/>
242     
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245
246    <p><font color="gray" size="-3">&nbsp;&nbsp;Produced by IDLdoc 2.0.</font></p>
247
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