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74<a href="inrecgrid.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?format=raw" 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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82      <h2 class="pro_file">ll_narcs_distances.pro</h2>
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85        <dl>
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90 This function returns the longitude and latitude [lon, lat] of
91a point a given arc distance (-pi <= Arc_Dist <= pi), and azimuth (Az),
92from a specified location Lon0, lat0.
93       Same as LL_ARC_DISTANCE but for n points without do loop.
94
95
96Formula from Map Projections - a working manual.  USGS paper
971395.  Equations (5-5) and (5-6).
98</div>
99
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104     
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106     
107
108      <div id="routine_details">
109       
110
111        <div class="routine_details" id="_LL_NARCS_DISTANCES">
112
113          <h2><a class="top" href="#container">top</a>LL_NARCS_DISTANCES <span class="categories"> 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="value">
123 a (2, n) array containing the
124       longitude / latitude of the resultings points. Values are in radians
125       unless the keyword DEGREES is set.
126</div>
127
128         
129            <h3>Parameters</h3>
130       
131           
132            <h4 id="_LL_NARCS_DISTANCES_param_lon0">lon0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
133              <span class="attr">in</span>
134             
135             
136              <span class="attr">required</span>
137             
138             
139             
140             
141            </h4>
142       
143          <div class="comments">  An array containing the longitude of the starting point.
144             Values are assumed to be in radians unless the keyword
145             DEGREES is set.</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">  An array containing the latitude of the starting point.
159             Values are assumed to be in radians unless the keyword
160             DEGREES is set.</div>
161           
162            <h4 id="_LL_NARCS_DISTANCES_param_arc_dist">arc_dist&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
163              <span class="attr">in</span>
164             
165             
166              <span class="attr">required</span>
167             
168             
169             
170             
171            </h4>
172       
173          <div class="comments">  The arc distance from Lon_lat0. The value must be between
174 -!PI and +!PI. To express distances in arc units, divide
175  by the radius of the globe expressed in the original units.
176  For example, if the radius of the earth is 6371 km, divide
177  the distance in km by 6371 to obtain the arc distance.    </div>
178           
179            <h4 id="_LL_NARCS_DISTANCES_param_az">az&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
180              <span class="attr">in</span>
181             
182             
183              <span class="attr">required</span>
184             
185             
186             
187             
188            </h4>
189       
190          <div class="comments">   The azimuth from Lon_lat0. The value is assumed to be in
191  radians unless the keyword DEGREES is set.
192</div>
193           
194
195         
196
197         
198
199            <h3>Keywords</h3>
200           
201            <h4 id="_LL_NARCS_DISTANCES_keyword_DEGREES">DEGREES&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
202             
203             
204             
205             
206             
207             
208             
209             
210            </h4>
211       
212            <div class="comments">  Set this keyword to express all measurements and
213  results in degrees.
214</div>
215           
216         
217
218          <h3>Examples</h3><div class="value"> 
219Result = LL_NARCS_DISTANCES(Lon, lat0, Arc_Dist, Az)
220
221 
222Lon_lat0 = [1.0, 2.0]; Initial point specified in radians
223Arc_Dist = 2.0; Arc distance in radians
224Az = 1.0; Azimuth in radians
225Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az)
226PRINT, Result
227       2.91415    -0.622234
228
229IDL> lon0 = [-10, 20, 100]
230IDL> lat0 = [0, -10, 45]
231IDL> lon1 = [10, 60, 280]
232IDL> lat1 = [0, 10, 45]
233IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two)
234IDL> earthradius = 6378206.4d0
235IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees)
236IDL> print, reform(res[0, *])
237       10.000000       60.000000       280.00000
238IDL> print, reform(res[1, *])
239          1.1999280e-15       10.000000       45.000000
240</div>
241          <h3>Version history</h3>
242         
243         
244          <h4>History</h4><div class="value">
245       Based on the IDL function ll_arc_distance.pro,v 1.11 2003/02/03
246 Sebastien Masson (smasson@lodyc.jussieu.fr)
247                  August 2005</div>
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