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74<a href="lbcorca.html">&lt;&lt;prev file</a> | <a href="map_npoints.html">next file &gt;&gt;</a>&nbsp;&nbsp;&nbsp;&nbsp;<a href="ll_narcs_distances.html" target="_TOP">view single page</a> | <a href="./../index.html" target="_TOP">view frames</a>&nbsp;&nbsp;&nbsp;&nbsp;summary: fields | routine&nbsp;&nbsp;&nbsp;&nbsp;details: <a href="#routine_details">routine</a>
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81      <h1 class="directory"><a href="directory-overview.html">Interpolation/</a></h1>
82      <h2 class="pro_file">ll_narcs_distances.pro</h2>
83
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85        <dl>
86        </dl>
87      </div>
88
89      <div id="file_comments">
90 This function returns the longitude and latitude [lon, lat] of
91 a point a given arc distance (-pi <= Arc_Dist <= pi), and azimuth (Az),
92 from a specified location Lon0, Lat0.
93 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.
94
95 Formula from Map Projections - a working manual.  USGS paper
96 1395. Equations (5-5) and (5-6).
97</div>
98
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105     
106
107      <div id="routine_details">
108       
109
110        <div class="routine_details" id="_ll_narcs_distances">
111
112          <h2><a class="top" href="#container">top</a>ll_narcs_distances <span class="categories">
113 Mapping, geography
114</span></h2>
115       
116          <p class="header">
117            <span class="result">result = </span>ll_narcs_distances(<span class="result"><a href="#_ll_narcs_distances_param_lon0">lon0</a>, <a href="#_ll_narcs_distances_param_lat0">lat0</a>, <a href="#_ll_narcs_distances_param_arc_dist">arc_dist</a>, <a href="#_ll_narcs_distances_param_az">az</a></span>, <a href="#_ll_narcs_distances_keyword_DEGREES">DEGREES</a>=<span class="result">DEGREES</span>)</p>
118       
119          <div class="comments">
120</div>
121
122          <h3>Return value</h3><div class="preformat">
123 a (2,n) array containing the longitude/latitude of the resulting points.
124 Values are in radians unless the keyword DEGREES is set.
125</div>
126
127         
128            <h3>Parameters</h3>
129       
130           
131            <h4 id="_ll_narcs_distances_param_lon0">lon0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
132              <span class="attr">in</span>
133             
134             
135              <span class="attr">required</span>
136             
137             
138             
139             
140            </h4>
141       
142          <div class="comments">
143 An array containing the longitude of the starting point.
144 Values are assumed to be in radians unless the keyword DEGREES is set.
145</div>
146           
147            <h4 id="_ll_narcs_distances_param_lat0">lat0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
148              <span class="attr">in</span>
149             
150             
151              <span class="attr">required</span>
152             
153             
154             
155             
156            </h4>
157       
158          <div class="comments">
159 An array containing the latitude of the starting point.
160 Values are assumed to be in radians unless the keyword DEGREES is set.
161</div>
162           
163            <h4 id="_ll_narcs_distances_param_arc_dist">arc_dist&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
164              <span class="attr">in</span>
165             
166             
167              <span class="attr">required</span>
168             
169             
170             
171             
172            </h4>
173       
174          <div class="comments">
175 The arc distance from Lon_lat0. The value must be between
176 -!PI and +!PI. To express distances in arc units, divide
177  by the radius of the globe expressed in the original units.
178  For example, if the radius of the earth is 6371 km, divide
179  the distance in km by 6371 to obtain the arc distance.
180</div>
181           
182            <h4 id="_ll_narcs_distances_param_az">az&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
183              <span class="attr">in</span>
184             
185             
186              <span class="attr">required</span>
187             
188             
189             
190             
191            </h4>
192       
193          <div class="comments">
194 The azimuth from Lon_lat0. The value is assumed to be in
195 radians unless the keyword DEGREES is set.
196</div>
197           
198
199         
200
201         
202
203            <h3>Keywords</h3>
204           
205            <h4 id="_ll_narcs_distances_keyword_DEGREES">DEGREES&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
206             
207             
208             
209             
210             
211             
212             
213             
214            </h4>
215       
216            <div class="comments">
217 Set this keyword to express all measurements and results in degrees.
218</div>
219           
220         
221
222          <h3>Examples</h3><div class="preformat">
223 IDL> Lon_lat0 = [1.0, 2.0]; Initial point specified in radians
224 IDL> Arc_Dist = 2.0; Arc distance in radians
225 IDL> Az = 1.0; Azimuth in radians
226 IDL> Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az)
227 IDL> PRINT, Result
228       2.91415    -0.622234
229
230 IDL> lon0 = [-10, 20, 100]
231 IDL> lat0 = [0, -10, 45]
232 IDL> lon1 = [10, 60, 280]
233 IDL> lat1 = [0, 10, 45]
234 IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two)
235 IDL> earthradius = 6378206.4d0
236 IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees)
237 IDL> print, reform(res[0, *])
238       10.000000       60.000000       280.00000
239 IDL> print, reform(res[1, *])
240           1.1999280e-15       10.000000       45.000000
241</div>
242          <h3>Version history</h3>
243         
244          <h4>Version</h4><div class="preformat">
245 $Id: ll_narcs_distances.pro 327 2007-12-13 16:22:35Z pinsard $
246</div>
247          <h4>History</h4><div class="preformat">
248       Based on the IDL function ll_arc_distance.pro,v 1.11 2003/02/03
249 Sebastien Masson (smasson@lodyc.jussieu.fr)
250                  August 2005
251</div>
252         
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267       
268          <h3>Statistics</h3>
269          <table class="statistics">
270            <tr><td>McCabe cyclic</td><td>           5</td></tr>
271            <tr><td>McCabe essential</td><td>           1</td></tr>
272            <tr><td>McCabe modular design</td><td>           1</td></tr>
273          </table>
274         
275       
276        </div>
277       
278      </div>
279
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281
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