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   1 /*
   2  * Copyright © 2010 Keith Packard <keithp@keithp.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; version 2 of the License.
   7  *
   8  * This program is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  16  */
  17
  18 package altosui;
  19
  20 import altosui.AltosGPS;
  21
  22 import java.lang.Math;
  23
  24 public class AltosGreatCircle {
  25         double  distance;
  26         double  bearing;
  27
  28         double sqr(double a) { return a * a; }
  29
  30         static final double rad = Math.PI / 180;
  31         static final double earth_radius = 6371.2 * 1000;       /* in meters */
  32
  33         public AltosGreatCircle (double start_lat, double start_lon,
  34                                  double end_lat, double end_lon)
  35         {
  36                 double lat1 = rad * start_lat;
  37                 double lon1 = rad * -start_lon;
  38                 double lat2 = rad * end_lat;
  39                 double lon2 = rad * -end_lon;
  40
  41                 double d_lon = lon2 - lon1;
  42
  43                 /* From http://en.wikipedia.org/wiki/Great-circle_distance */
  44                 double vdn = Math.sqrt(sqr(Math.cos(lat2) * Math.sin(d_lon)) +
  45                                        sqr(Math.cos(lat1) * Math.sin(lat2) -
  46                                            Math.sin(lat1) * Math.cos(lat2) * Math.cos(d_lon)));
  47                 double vdd = Math.sin(lat1) * Math.sin(lat2) + Math.cos(lat1) * Math.cos(lat2) * Math.cos(d_lon);
  48                 double d = Math.atan2(vdn,vdd);
  49                 double course;
  50
  51                 if (Math.cos(lat1) < 1e-20) {
  52                         if (lat1 > 0)
  53                                 course = Math.PI;
  54                         else
  55                                 course = -Math.PI;
  56                 } else {
  57                         if (d < 1e-10)
  58                                 course = 0;
  59                         else
  60                                 course = Math.acos((Math.sin(lat2)-Math.sin(lat1)*Math.cos(d)) /
  61                                                    (Math.sin(d)*Math.cos(lat1)));
  62                         if (Math.sin(lon2-lon1) > 0)
  63                                 course = 2 * Math.PI-course;
  64                 }
  65                 distance = d * earth_radius;
  66                 bearing = course * 180/Math.PI;
  67         }
  68
  69         public AltosGreatCircle(AltosGPS start, AltosGPS end) {
  70                 this(start.lat, start.lon, end.lat, end.lon);
  71         }
  72
  73         public AltosGreatCircle() {
  74                 distance = 0;
  75                 bearing = 0;
  76         }
  77 }