//
// Written by Curtis Olson, started June 1997.
//
-// Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
+// Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
//
-// 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; either version 2 of the
-// License, or (at your option) any later version.
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Library General Public
+// License as published by the Free Software Foundation; either
+// version 2 of the License, or (at your option) any later version.
//
-// This program is distributed in the hope that it will be useful, but
-// WITHOUT ANY WARRANTY; without even the implied warranty of
+// This library 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.
+// Library 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
// $Id$
+#ifdef HAVE_CONFIG_H
+# include <simgear_config.h>
+#endif
#include <math.h>
-#include <stdio.h>
#include <simgear/constants.h>
#include "polar3d.hxx"
+/**
+ * Calculate new lon/lat given starting lon/lat, and offset radial, and
+ * distance. NOTE: starting point is specifed in radians, distance is
+ * specified in meters (and converted internally to radians)
+ * ... assumes a spherical world.
+ * @param orig specified in polar coordinates
+ * @param course offset radial
+ * @param dist offset distance
+ * @return destination point in polar coordinates
+ */
+Point3D calc_gc_lon_lat( const Point3D& orig, double course,
+ double dist ) {
+ Point3D result;
-// Find the Altitude above the Ellipsoid (WGS84) given the Earth
-// Centered Cartesian coordinate vector Distances are specified in
-// meters.
-double fgGeodAltFromCart(const Point3D& cp)
-{
- double t_lat, x_alpha, mu_alpha;
- double lat_geoc, radius;
- double result;
-
- lat_geoc = FG_PI_2 - atan2( sqrt(cp.x()*cp.x() + cp.y()*cp.y()), cp.z() );
- radius = sqrt( cp.x()*cp.x() + cp.y()*cp.y() + cp.z()*cp.z() );
-
- if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) // near North pole
- || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) // near South pole
- {
- result = radius - EQUATORIAL_RADIUS_M*E;
+ // lat=asin(sin(lat1)*cos(d)+cos(lat1)*sin(d)*cos(tc))
+ // IF (cos(lat)=0)
+ // lon=lon1 // endpoint a pole
+ // ELSE
+ // lon=mod(lon1-asin(sin(tc)*sin(d)/cos(lat))+pi,2*pi)-pi
+ // ENDIF
+
+ // printf("calc_lon_lat() offset.theta = %.2f offset.dist = %.2f\n",
+ // offset.theta, offset.dist);
+
+ dist *= SG_METER_TO_NM * SG_NM_TO_RAD;
+
+ result.sety( asin( sin(orig.y()) * cos(dist) +
+ cos(orig.y()) * sin(dist) * cos(course) ) );
+
+ if ( cos(result.y()) < SG_EPSILON ) {
+ result.setx( orig.x() ); // endpoint a pole
} else {
- t_lat = tan(lat_geoc);
- x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
- mu_alpha = atan2(sqrt(RESQ_M - x_alpha*x_alpha),E*x_alpha);
- if (lat_geoc < 0) {
- mu_alpha = - mu_alpha;
- }
- result = (radius - x_alpha/cos(lat_geoc))*cos(mu_alpha - lat_geoc);
+ result.setx(
+ fmod(orig.x() - asin( sin(course) * sin(dist) /
+ cos(result.y()) )
+ + SGD_PI, SGD_2PI) - SGD_PI );
}
- return(result);
+ return result;
}
+/**
+ * Calculate course/dist given two spherical points.
+ * @param start starting point
+ * @param dest ending point
+ * @param course resulting course
+ * @param dist resulting distance
+ */
+void calc_gc_course_dist( const Point3D& start, const Point3D& dest,
+ double *course, double *dist )
+{
+ if ( start == dest) {
+ *dist=0;
+ *course=0;
+ return;
+ }
+ // d = 2*asin(sqrt((sin((lat1-lat2)/2))^2 +
+ // cos(lat1)*cos(lat2)*(sin((lon1-lon2)/2))^2))
+ double cos_start_y = cos( start.y() );
+ double tmp1 = sin( (start.y() - dest.y()) * 0.5 );
+ double tmp2 = sin( (start.x() - dest.x()) * 0.5 );
+ double d = 2.0 * asin( sqrt( tmp1 * tmp1 +
+ cos_start_y * cos(dest.y()) * tmp2 * tmp2));
+ *dist = d * SG_RAD_TO_NM * SG_NM_TO_METER;
+
+#if 1
+ double c1 = atan2(
+ cos(dest.y())*sin(dest.x()-start.x()),
+ cos(start.y())*sin(dest.y())-
+ sin(start.y())*cos(dest.y())*cos(dest.x()-start.x()));
+ if (c1 >= 0)
+ *course = SGD_2PI-c1;
+ else
+ *course = -c1;
+#else
+ // We obtain the initial course, tc1, (at point 1) from point 1 to
+ // point 2 by the following. The formula fails if the initial
+ // point is a pole. We can special case this with:
+ //
+ // IF (cos(lat1) < EPS) // EPS a small number ~ machine precision
+ // IF (lat1 > 0)
+ // tc1= pi // starting from N pole
+ // ELSE
+ // tc1= 0 // starting from S pole
+ // ENDIF
+ // ENDIF
+ //
+ // For starting points other than the poles:
+ //
+ // IF sin(lon2-lon1)<0
+ // tc1=acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
+ // ELSE
+ // tc1=2*pi-acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
+ // ENDIF
+
+ // if ( cos(start.y()) < SG_EPSILON ) {
+ // doing it this way saves a transcendental call
+ double sin_start_y = sin( start.y() );
+ if ( fabs(1.0-sin_start_y) < SG_EPSILON ) {
+ // EPS a small number ~ machine precision
+ if ( start.y() > 0 ) {
+ *course = SGD_PI; // starting from N pole
+ } else {
+ *course = 0; // starting from S pole
+ }
+ } else {
+ // For starting points other than the poles:
+ // double tmp3 = sin(d)*cos_start_y);
+ // double tmp4 = sin(dest.y())-sin(start.y())*cos(d);
+ // double tmp5 = acos(tmp4/tmp3);
+
+ // Doing this way gaurentees that the temps are
+ // not stored into memory
+ double tmp5 = acos( (sin(dest.y()) - sin_start_y * cos(d)) /
+ (sin(d) * cos_start_y) );
+
+ // if ( sin( dest.x() - start.x() ) < 0 ) {
+ // the sin of the negative angle is just the opposite sign
+ // of the sin of the angle so tmp2 will have the opposite
+ // sign of sin( dest.x() - start.x() )
+ if ( tmp2 >= 0 ) {
+ *course = tmp5;
+ } else {
+ *course = SGD_2PI - tmp5;
+ }
+ }
+#endif
+}
+
+
+#if 0
+/**
+ * Calculate course/dist given two spherical points.
+ * @param start starting point
+ * @param dest ending point
+ * @param course resulting course
+ * @param dist resulting distance
+ */
+void calc_gc_course_dist( const Point3D& start, const Point3D& dest,
+ double *course, double *dist ) {
+ // d = 2*asin(sqrt((sin((lat1-lat2)/2))^2 +
+ // cos(lat1)*cos(lat2)*(sin((lon1-lon2)/2))^2))
+ double tmp1 = sin( (start.y() - dest.y()) / 2 );
+ double tmp2 = sin( (start.x() - dest.x()) / 2 );
+ double d = 2.0 * asin( sqrt( tmp1 * tmp1 +
+ cos(start.y()) * cos(dest.y()) * tmp2 * tmp2));
+ // We obtain the initial course, tc1, (at point 1) from point 1 to
+ // point 2 by the following. The formula fails if the initial
+ // point is a pole. We can special case this with:
+ //
+ // IF (cos(lat1) < EPS) // EPS a small number ~ machine precision
+ // IF (lat1 > 0)
+ // tc1= pi // starting from N pole
+ // ELSE
+ // tc1= 0 // starting from S pole
+ // ENDIF
+ // ENDIF
+ //
+ // For starting points other than the poles:
+ //
+ // IF sin(lon2-lon1)<0
+ // tc1=acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
+ // ELSE
+ // tc1=2*pi-acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
+ // ENDIF
+
+ double tc1;
+
+ if ( cos(start.y()) < SG_EPSILON ) {
+ // EPS a small number ~ machine precision
+ if ( start.y() > 0 ) {
+ tc1 = SGD_PI; // starting from N pole
+ } else {
+ tc1 = 0; // starting from S pole
+ }
+ }
+
+ // For starting points other than the poles:
+
+ double tmp3 = sin(d)*cos(start.y());
+ double tmp4 = sin(dest.y())-sin(start.y())*cos(d);
+ double tmp5 = acos(tmp4/tmp3);
+ if ( sin( dest.x() - start.x() ) < 0 ) {
+ tc1 = tmp5;
+ } else {
+ tc1 = SGD_2PI - tmp5;
+ }
+
+ *course = tc1;
+ *dist = d * SG_RAD_TO_NM * SG_NM_TO_METER;
+}
+#endif // 0
projects / simgear.git / blobdiff