1 /**************************************************************************
2 * polar.cxx -- routines to deal with polar math and transformations
4 * Written by Curtis Olson, started June 1997.
6 * Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of the
11 * License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
23 * (Log is kept at end of this file)
24 **************************************************************************/
30 #include <Include/fg_constants.h>
32 #include "polar3d.hxx"
35 /* Convert a polar coordinate to a cartesian coordinate. Lon and Lat
36 * must be specified in radians. The FG convention is for distances
37 * to be specified in meters */
38 fgPoint3d fgPolarToCart3d(fgPoint3d p) {
42 tmp = cos(p.lat) * p.radius;
44 pnew.x = cos(p.lon) * tmp;
45 pnew.y = sin(p.lon) * tmp;
46 pnew.z = sin(p.lat) * p.radius;
52 /* Convert a cartesian coordinate to polar coordinates (lon/lat
53 * specified in radians. Distances are specified in meters. */
54 fgPoint3d fgCartToPolar3d(fgPoint3d cp) {
57 pp.lon = atan2( cp.y, cp.x );
58 pp.lat = FG_PI_2 - atan2( sqrt(cp.x*cp.x + cp.y*cp.y), cp.z );
59 pp.radius = sqrt(cp.x*cp.x + cp.y*cp.y + cp.z*cp.z);
61 /* printf("lon = %.2f lat = %.2f radius = %.2f\n",
62 pp.lon, pp.lat, pp.radius); */
67 /* Find the Altitude above the Ellipsoid (WGS84) given the Earth
68 * Centered Cartesian coordinate vector Distances are specified in
70 double fgGeodAltFromCart(fgPoint3d cp)
72 double t_lat, x_alpha, mu_alpha;
73 double lat_geoc, radius;
76 lat_geoc = FG_PI_2 - atan2( sqrt(cp.x*cp.x + cp.y*cp.y), cp.z );
77 radius = sqrt(cp.x*cp.x + cp.y*cp.y + cp.z*cp.z);
79 if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) /* near North pole */
80 || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) /* near South pole */
82 result = radius - EQUATORIAL_RADIUS_M*E;
84 t_lat = tan(lat_geoc);
85 x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
86 mu_alpha = atan2(sqrt(RESQ_M - x_alpha*x_alpha),E*x_alpha);
88 mu_alpha = - mu_alpha;
90 result = (radius - x_alpha/cos(lat_geoc))*cos(mu_alpha - lat_geoc);
98 /* Revision 1.2 1998/08/24 20:04:11 curt
99 /* Various "inline" code optimizations contributed by Norman Vine.
101 * Revision 1.1 1998/07/08 14:40:08 curt
102 * polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
103 * Updated fg_geodesy comments to reflect that routines expect and produce
106 * Revision 1.2 1998/05/03 00:45:49 curt
107 * Commented out a debugging printf.
109 * Revision 1.1 1998/05/02 01:50:11 curt
110 * polar.[ch] renamed to polar3d.[ch]
112 * Revision 1.6 1998/04/25 22:06:23 curt
113 * Edited cvs log messages in source files ... bad bad bad!
115 * Revision 1.5 1998/01/27 00:48:00 curt
116 * Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
117 * system and commandline/config file processing code.
119 * Revision 1.4 1998/01/19 19:27:12 curt
120 * Merged in make system changes from Bob Kuehne <rpk@sgi.com>
121 * This should simplify things tremendously.
123 * Revision 1.3 1997/12/15 23:54:54 curt
124 * Add xgl wrappers for debugging.
125 * Generate terrain normals on the fly.
127 * Revision 1.2 1997/07/31 22:52:27 curt
128 * Working on redoing internal coordinate systems & scenery transformations.
130 * Revision 1.1 1997/07/07 21:02:36 curt