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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 org.altusmetrum.altoslib_4;
  19
  20 import java.lang.Math;
  21
  22 public class AltosGreatCircle implements Cloneable {
  23         public double   distance;
  24         public double   bearing;
  25         public double   range;
  26         public double   elevation;
  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 static final int BEARING_LONG = AltosConvert.BEARING_LONG;
  34         public static final int BEARING_SHORT = AltosConvert.BEARING_SHORT;
  35         public static final int BEARING_VOICE = AltosConvert.BEARING_VOICE;
  36
  37         public String bearing_words(int length) {
  38                 return AltosConvert.bearing_to_words(length, bearing);
  39         }
  40
  41         public AltosGreatCircle (double start_lat, double start_lon, double start_alt,
  42                                  double end_lat, double end_lon, double end_alt) {
  43                 double lat1 = rad * start_lat;
  44                 double lon1 = rad * -start_lon;
  45                 double lat2 = rad * end_lat;
  46                 double lon2 = rad * -end_lon;
  47
  48                 double d_lon = lon2 - lon1;
  49
  50                 /* From http://en.wikipedia.org/wiki/Great-circle_distance */
  51                 double vdn = Math.sqrt(sqr(Math.cos(lat2) * Math.sin(d_lon)) +
  52                                        sqr(Math.cos(lat1) * Math.sin(lat2) -
  53                                            Math.sin(lat1) * Math.cos(lat2) * Math.cos(d_lon)));
  54                 double vdd = Math.sin(lat1) * Math.sin(lat2) + Math.cos(lat1) * Math.cos(lat2) * Math.cos(d_lon);
  55                 double d = Math.atan2(vdn,vdd);
  56                 double course;
  57
  58                 if (Math.cos(lat1) < 1e-20) {
  59                         if (lat1 > 0)
  60                                 course = Math.PI;
  61                         else
  62                                 course = -Math.PI;
  63                 } else {
  64                         if (d < 1e-10)
  65                                 course = 0;
  66                         else
  67                                 course = Math.acos((Math.sin(lat2)-Math.sin(lat1)*Math.cos(d)) /
  68                                                    (Math.sin(d)*Math.cos(lat1)));
  69                         if (Math.sin(lon2-lon1) > 0)
  70                                 course = 2 * Math.PI-course;
  71                 }
  72                 distance = d * earth_radius;
  73                 bearing = course * 180/Math.PI;
  74
  75                 double height_diff = end_alt - start_alt;
  76                 range = Math.sqrt(distance * distance + height_diff * height_diff);
  77                 elevation = Math.atan2(height_diff, distance) * 180 / Math.PI;
  78         }
  79
  80         public AltosGreatCircle clone() {
  81                 AltosGreatCircle n = new AltosGreatCircle();
  82
  83                 n.distance = distance;
  84                 n.bearing = bearing;
  85                 n.range = range;
  86                 n.elevation = elevation;
  87                 return n;
  88         }
  89
  90         public AltosGreatCircle (double start_lat, double start_lon,
  91                                  double end_lat, double end_lon) {
  92                 this(start_lat, start_lon, 0, end_lat, end_lon, 0);
  93         }
  94
  95         public AltosGreatCircle(AltosGPS start, AltosGPS end) {
  96                 this(start.lat, start.lon, start.alt, end.lat, end.lon, end.alt);
  97         }
  98
  99         public AltosGreatCircle() {
 100                 distance = 0;
 101                 bearing = 0;
 102                 range = 0;
 103                 elevation = 0;
 104         }
 105 }