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trunk/SRC/Documentation/idldoc_html_output/Interpolation/ll_narcs_distances.html
r89 r101 87 87 </div> 88 88 89 <div id="file_comments"></div> 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 LL_ARC_DISTANCE but for n points without do loop. 94 95 96 Formula from Map Projections - a working manual. USGS paper 97 1395. Equations (5-5) and (5-6). 98 </div> 90 99 91 100 … … 102 111 <div class="routine_details" id="_LL_NARCS_DISTANCES"> 103 112 104 <h2><a class="top" href="#container">top</a>LL_NARCS_DISTANCES </h2> 113 <h2><a class="top" href="#container">top</a>LL_NARCS_DISTANCES <span class="categories"> Mapping, geography 114 </span></h2> 105 115 106 116 <p class="header"> … … 108 118 109 119 <div class="comments"> 110 NAME: 111 LL_NARCS_DISTANCES 112 113 PURPOSE: 114 This function returns the longitude and latitude [lon, lat] of 115 a point a given arc distance (-pi <= Arc_Dist <= pi), and azimuth (Az), 116 from a specified location Lon0, lat0. 117 Same as LL_ARC_DISTANCE but for n points without do loop. 118 119 CATEGORY: 120 Mapping, geography. 121 122 CALLING SEQUENCE: 123 Result = LL_NARCS_DISTANCES(Lon, lat0, Arc_Dist, Az) 124 125 INPUTS: 126 Lon0: An array containing the longitude of the starting point. 127 Values are assumed to be in radians unless the keyword 128 DEGREES is set. 129 Lat0: An array containing the latitude of the starting point. 130 Values are assumed to be in radians unless the keyword 131 DEGREES is set. 132 Arc_Dist: The arc distance from Lon_lat0. The value must be between 133 -!PI and +!PI. To express distances in arc units, divide 134 by the radius of the globe expressed in the original units. 135 For example, if the radius of the earth is 6371 km, divide 136 the distance in km by 6371 to obtain the arc distance. 137 Az: The azimuth from Lon_lat0. The value is assumed to be in 138 radians unless the keyword DEGREES is set. 139 140 KEYWORD PARAMETERS: 141 DEGREES: Set this keyword to express all measurements and 142 results in degrees. 143 144 OUTPUTS: 145 This function returns a (2, n) array containing the 120 </div> 121 122 <h3>Return value</h3><div class="value"> 123 a (2, n) array containing the 146 124 longitude / latitude of the resultings points. Values are in radians 147 125 unless the keyword DEGREES is set. 148 149 PROCEDURE: 150 Formula from Map Projections - a working manual. USGS paper 151 1395. Equations (5-5) and (5-6). 152 153 EXAMPLE: 154 Lon_lat0 = [1.0, 2.0] ; Initial point specified in radians 155 Arc_Dist = 2.0 ; Arc distance in radians 156 Az = 1.0 ; Azimuth in radians 157 Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az) 158 PRINT, Result 159 2.91415 -0.622234 160 161 IDL> lon0 = [-10, 20, 100] 162 IDL> lat0 = [0, -10, 45] 163 IDL> lon1 = [10, 60, 280] 164 IDL> lat1 = [0, 10, 45] 165 IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two) 166 IDL> earthradius = 6378206.4d0 167 IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees) 168 IDL> print, reform(res[0, *]) 169 10.000000 60.000000 280.00000 170 IDL> print, reform(res[1, *]) 126 </div> 127 128 129 <h3>Parameters</h3> 130 131 132 <h4 id="_LL_NARCS_DISTANCES_param_lon0">lon0 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 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 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 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 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"> 219 Result = LL_NARCS_DISTANCES(Lon, lat0, Arc_Dist, Az) 220 221 222 Lon_lat0 = [1.0, 2.0]; Initial point specified in radians 223 Arc_Dist = 2.0; Arc distance in radians 224 Az = 1.0; Azimuth in radians 225 Result = LL_ARC_DISTANCE(Lon_lat0, Arc_Dist, Az) 226 PRINT, Result 227 2.91415 -0.622234 228 229 IDL> lon0 = [-10, 20, 100] 230 IDL> lat0 = [0, -10, 45] 231 IDL> lon1 = [10, 60, 280] 232 IDL> lat1 = [0, 10, 45] 233 IDL> dist = map_npoints(lon0, lat0, lon1, lat1, azimuth = azi, /two_by_two) 234 IDL> earthradius = 6378206.4d0 235 IDL> res = ll_narcs_distances(lon0, lat0, dist/earthradius, azi, /degrees) 236 IDL> print, reform(res[0, *]) 237 10.000000 60.000000 280.00000 238 IDL> print, reform(res[1, *]) 171 239 1.1999280e-15 10.000000 45.000000 172 173 MODIFICATION HISTORY: 174 Based on the IDL function ll_arc_distance.pro,v 1.11 2003/02/03</div> 175 176 177 178 179 <h3>Parameters</h3> 180 181 182 <h4 id="_LL_NARCS_DISTANCES_param_lon0">lon0 183 184 185 186 187 188 189 190 191 </h4> 192 193 <div class="comments"></div> 194 195 <h4 id="_LL_NARCS_DISTANCES_param_lat0">lat0 196 197 198 199 200 201 202 203 204 </h4> 205 206 <div class="comments"></div> 207 208 <h4 id="_LL_NARCS_DISTANCES_param_arc_dist">arc_dist 209 210 211 212 213 214 215 216 217 </h4> 218 219 <div class="comments"></div> 220 221 <h4 id="_LL_NARCS_DISTANCES_param_az">az 222 223 224 225 226 227 228 229 230 </h4> 231 232 <div class="comments"></div> 233 234 235 236 237 238 239 <h3>Keywords</h3> 240 241 <h4 id="_LL_NARCS_DISTANCES_keyword_DEGREES">DEGREES 242 243 244 245 246 247 248 249 250 </h4> 251 252 <div class="comments"></div> 253 254 255 256 257 258 259 260 240 </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> 261 248 262 249
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