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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>
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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 LL_ARC_DISTANCE 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"> Mapping, geography
79</font></h2>
80
81      <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>
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83   
84
85
86    <h3>Return value</h3>
87 a (2, n) array containing the longitude/latitude of the resulting points.
88 Values are in radians unless the keyword DEGREES is set.
89
90
91   
92    <h3>Parameters</h3>
93   
94
95    <a name="#_ll_narcs_distances_keyword_lon0"></a>
96    <h4>lon0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
97      <font size="-1" color="#006633">in</font>
98     
99     
100      <font size="-1" color="#006633">required</font>
101     
102     
103     
104     
105    </h4>
106
107   
108 An array containing the longitude of the starting point.
109 Values are assumed to be in radians unless the keyword DEGREES is set.
110
111   
112
113    <a name="#_ll_narcs_distances_keyword_lat0"></a>
114    <h4>lat0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
115      <font size="-1" color="#006633">in</font>
116     
117     
118      <font size="-1" color="#006633">required</font>
119     
120     
121     
122     
123    </h4>
124
125   
126 An array containing the latitude of the starting point.
127 Values are assumed to be in radians unless the keyword DEGREES is set.
128
129   
130
131    <a name="#_ll_narcs_distances_keyword_arc_dist"></a>
132    <h4>arc_dist&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
133      <font size="-1" color="#006633">in</font>
134     
135     
136      <font size="-1" color="#006633">required</font>
137     
138     
139     
140     
141    </h4>
142
143   
144 The arc distance from Lon_lat0. The value must be between
145 -!PI and +!PI. To express distances in arc units, divide
146  by the radius of the globe expressed in the original units.
147  For example, if the radius of the earth is 6371 km, divide
148  the distance in km by 6371 to obtain the arc distance.
149
150   
151
152    <a name="#_ll_narcs_distances_keyword_az"></a>
153    <h4>az&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
154      <font size="-1" color="#006633">in</font>
155     
156     
157      <font size="-1" color="#006633">required</font>
158     
159     
160     
161     
162    </h4>
163
164   
165 The azimuth from Lon_lat0. The value is assumed to be in
166 radians unless the keyword DEGREES is set.
167
168   
169   
170
171   
172    <h3>Keywords</h3>
173
174   
175    <a name="#_ll_narcs_distances_keyword_DEGREES"></a>
176    <h4>DEGREES&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
177     
178     
179     
180     
181     
182     
183     
184     
185    </h4>
186
187   
188 Set this keyword to express all measurements and results in degrees.
189
190   
191   
192
193    <h3>Examples</h3>
194 IDL> Lon_lat0 = [1.0, 2.0]; Initial point specified in radians
195 IDL> Arc_Dist = 2.0; Arc distance in radians
196 IDL> Az = 1.0; Azimuth in radians
197 IDL> Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az)
198 IDL> PRINT, Result
199       2.91415    -0.622234
200
201 IDL> lon0 = [-10, 20, 100]
202 IDL> lat0 = [0, -10, 45]
203 IDL> lon1 = [10, 60, 280]
204 IDL> lat1 = [0, 10, 45]
205 IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two)
206 IDL> earthradius = 6378206.4d0
207 IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees)
208 IDL> print, reform(res[0, *])
209       10.000000       60.000000       280.00000
210 IDL> print, reform(res[1, *])
211           1.1999280e-15       10.000000       45.000000
212
213    <h3>Version history</h3>
214   
215    <h4>Version</h4> $Id: ll_narcs_distances.pro 163 2006-08-29 12:59:46Z navarro $
216
217    <h4>History</h4>
218       Based on the IDL function ll_arc_distance.pro,v 1.11 2003/02/03
219 Sebastien Masson (smasson@lodyc.jussieu.fr)
220                  August 2005
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238    <font size="-3"><p>&nbsp;</p></font>
239    <hr size="1" color="#CCCCCC"/>
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244    <p><font color="gray" size="-3">&nbsp;&nbsp;Produced by IDLdoc 2.0 on Wed Sep  6 12:27:22 2006.</font></p>
245
246  </body>
247</html>
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