1 // polar.cxx -- routines to deal with polar math and transformations
3 // Written by Curtis Olson, started June 1997.
5 // Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
7 // This program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License as
9 // published by the Free Software Foundation; either version 2 of the
10 // License, or (at your option) any later version.
12 // This program is distributed in the hope that it will be useful, but
13 // WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
22 // (Log is kept at end of this file)
28 #include <Include/fg_constants.h>
30 #include "polar3d.hxx"
33 // Find the Altitude above the Ellipsoid (WGS84) given the Earth
34 // Centered Cartesian coordinate vector Distances are specified in
36 double fgGeodAltFromCart(const Point3D& cp)
38 double t_lat, x_alpha, mu_alpha;
39 double lat_geoc, radius;
42 lat_geoc = FG_PI_2 - atan2( sqrt(cp.x()*cp.x() + cp.y()*cp.y()), cp.z() );
43 radius = sqrt( cp.x()*cp.x() + cp.y()*cp.y() + cp.z()*cp.z() );
45 if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) // near North pole
46 || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) // near South pole
48 result = radius - EQUATORIAL_RADIUS_M*E;
50 t_lat = tan(lat_geoc);
51 x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
52 mu_alpha = atan2(sqrt(RESQ_M - x_alpha*x_alpha),E*x_alpha);
54 mu_alpha = - mu_alpha;
56 result = (radius - x_alpha/cos(lat_geoc))*cos(mu_alpha - lat_geoc);
64 // Revision 1.6 1999/01/27 04:46:19 curt
65 // Portability tweaks by Bernie Bright.
67 // Revision 1.5 1998/10/18 01:17:13 curt
70 // Revision 1.4 1998/10/16 19:30:09 curt
71 // C++-ified the comments.
73 // Revision 1.3 1998/10/16 00:50:29 curt
74 // Added point3d.hxx to replace cheezy fgPoint3d struct.
76 // Revision 1.2 1998/08/24 20:04:11 curt
77 // Various "inline" code optimizations contributed by Norman Vine.
79 // Revision 1.1 1998/07/08 14:40:08 curt
80 // polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
81 // Updated fg_geodesy comments to reflect that routines expect and produce
84 // Revision 1.2 1998/05/03 00:45:49 curt
85 // Commented out a debugging printf.
87 // Revision 1.1 1998/05/02 01:50:11 curt
88 // polar.[ch] renamed to polar3d.[ch]
90 // Revision 1.6 1998/04/25 22:06:23 curt
91 // Edited cvs log messages in source files ... bad bad bad!
93 // Revision 1.5 1998/01/27 00:48:00 curt
94 // Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
95 // system and commandline/config file processing code.
97 // Revision 1.4 1998/01/19 19:27:12 curt
98 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
99 // This should simplify things tremendously.
101 // Revision 1.3 1997/12/15 23:54:54 curt
102 // Add xgl wrappers for debugging.
103 // Generate terrain normals on the fly.
105 // Revision 1.2 1997/07/31 22:52:27 curt
106 // Working on redoing internal coordinate systems & scenery transformations.
108 // Revision 1.1 1997/07/07 21:02:36 curt