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/*
* Copyright © 2010 Keith Packard <keithp@keithp.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
package altosui;
import java.lang.Math;
public class AltosGreatCircle {
double distance;
double bearing;
double sqr(double a) { return a * a; }
static final double rad = Math.PI / 180;
static final double earth_radius = 6371.2 * 1000; /* in meters */
AltosGreatCircle (double start_lat, double start_lon,
double end_lat, double end_lon)
{
double lat1 = rad * start_lat;
double lon1 = rad * -start_lon;
double lat2 = rad * end_lat;
double lon2 = rad * -end_lon;
double d_lon = lon2 - lon1;
/* From http://en.wikipedia.org/wiki/Great-circle_distance */
double vdn = Math.sqrt(sqr(Math.cos(lat2) * Math.sin(d_lon)) +
sqr(Math.cos(lat1) * Math.sin(lat2) -
Math.sin(lat1) * Math.cos(lat2) * Math.cos(d_lon)));
double vdd = Math.sin(lat1) * Math.sin(lat2) + Math.cos(lat1) * Math.cos(lat2) * Math.cos(d_lon);
double d = Math.atan2(vdn,vdd);
double course;
if (Math.cos(lat1) < 1e-20) {
if (lat1 > 0)
course = Math.PI;
else
course = -Math.PI;
} else {
if (d < 1e-10)
course = 0;
else
course = Math.acos((Math.sin(lat2)-Math.sin(lat1)*Math.cos(d)) /
(Math.sin(d)*Math.cos(lat1)));
if (Math.sin(lon2-lon1) > 0)
course = 2 * Math.PI-course;
}
distance = d * earth_radius;
bearing = course * 180/Math.PI;
}
}
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