1 // fg_geodesy.cxx -- routines to convert between geodetic and geocentric
4 // Copied and adapted directly from LaRCsim/ls_geodesy.c
6 // See below for the complete original LaRCsim comments.
9 // (Log is kept at end of this file)
14 #include <Include/fg_constants.h>
15 #include <Math/fg_geodesy.hxx>
16 #include <Math/point3d.hxx>
19 // ONE_SECOND is pi/180/60/60, or about 100 feet at earths' equator
20 #define ONE_SECOND 4.848136811E-6
23 // fgGeocToGeod(lat_geoc, radius, *lat_geod, *alt, *sea_level_r)
25 // lat_geoc Geocentric latitude, radians, + = North
26 // radius C.G. radius to earth center (meters)
29 // lat_geod Geodetic latitude, radians, + = North
30 // alt C.G. altitude above mean sea level (meters)
31 // sea_level_r radius from earth center to sea level at
32 // local vertical (surface normal) of C.G. (meters)
35 void fgGeocToGeod( double lat_geoc, double radius, double
36 *lat_geod, double *alt, double *sea_level_r )
38 double t_lat, x_alpha, mu_alpha, delt_mu, r_alpha, l_point, rho_alpha;
39 double sin_mu_a, denom,delt_lambda, lambda_sl, sin_lambda_sl;
41 if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) // near North pole
42 || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) // near South pole
45 *sea_level_r = EQUATORIAL_RADIUS_M*E;
46 *alt = radius - *sea_level_r;
48 t_lat = tan(lat_geoc);
49 x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
50 mu_alpha = atan2(sqrt(RESQ_M - x_alpha*x_alpha),E*x_alpha);
51 if (lat_geoc < 0) mu_alpha = - mu_alpha;
52 sin_mu_a = sin(mu_alpha);
53 delt_lambda = mu_alpha - lat_geoc;
54 r_alpha = x_alpha/cos(lat_geoc);
55 l_point = radius - r_alpha;
56 *alt = l_point*cos(delt_lambda);
57 denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a);
58 rho_alpha = EQUATORIAL_RADIUS_M*(1-EPS)/
60 delt_mu = atan2(l_point*sin(delt_lambda),rho_alpha + *alt);
61 *lat_geod = mu_alpha - delt_mu;
62 lambda_sl = atan( E*E * tan(*lat_geod) ); // SL geoc. latitude
63 sin_lambda_sl = sin( lambda_sl );
65 sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
70 // fgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc )
72 // lat_geod Geodetic latitude, radians, + = North
73 // alt C.G. altitude above mean sea level (meters)
76 // sl_radius SEA LEVEL radius to earth center (meters)
77 // (add Altitude to get true distance from earth center.
78 // lat_geoc Geocentric latitude, radians, + = North
82 void fgGeodToGeoc( double lat_geod, double alt, double *sl_radius,
85 double lambda_sl, sin_lambda_sl, cos_lambda_sl, sin_mu, cos_mu, px, py;
87 lambda_sl = atan( E*E * tan(lat_geod) ); // sea level geocentric latitude
88 sin_lambda_sl = sin( lambda_sl );
89 cos_lambda_sl = cos( lambda_sl );
90 sin_mu = sin(lat_geod); // Geodetic (map makers') latitude
91 cos_mu = cos(lat_geod);
93 sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
94 py = *sl_radius*sin_lambda_sl + alt*sin_mu;
95 px = *sl_radius*cos_lambda_sl + alt*cos_mu;
96 *lat_geoc = atan2( py, px );
100 /***************************************************************************
104 ----------------------------------------------------------------------------
106 FUNCTION: Converts geocentric coordinates to geodetic positions
108 ----------------------------------------------------------------------------
110 MODULE STATUS: developmental
112 ----------------------------------------------------------------------------
114 GENEALOGY: Written as part of LaRCSim project by E. B. Jackson
116 ----------------------------------------------------------------------------
118 DESIGNED BY: E. B. Jackson
120 CODED BY: E. B. Jackson
122 MAINTAINED BY: E. B. Jackson
124 ----------------------------------------------------------------------------
126 MODIFICATION HISTORY:
130 930208 Modified to avoid singularity near polar region. EBJ
131 930602 Moved backwards calcs here from ls_step. EBJ
132 931214 Changed erroneous Latitude and Altitude variables to
133 *lat_geod and *alt in routine ls_geoc_to_geod. EBJ
134 940111 Changed header files from old ls_eom.h style to ls_types,
135 and ls_constants. Also replaced old DATA type with new
142 Revision 1.2 1998/10/16 23:36:36 curt
145 Revision 1.1 1998/10/16 19:30:40 curt
146 Renamed .c -> .h so we can start adding c++ supporting routines.
148 Revision 1.6 1998/07/08 14:40:07 curt
149 polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
150 Updated fg_geodesy comments to reflect that routines expect and produce
153 Revision 1.5 1998/04/25 22:06:23 curt
154 Edited cvs log messages in source files ... bad bad bad!
156 Revision 1.4 1998/01/27 00:47:59 curt
157 Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
158 system and commandline/config file processing code.
160 Revision 1.3 1998/01/19 19:27:12 curt
161 Merged in make system changes from Bob Kuehne <rpk@sgi.com>
162 This should simplify things tremendously.
164 Revision 1.2 1997/12/15 23:54:54 curt
165 Add xgl wrappers for debugging.
166 Generate terrain normals on the fly.
168 Revision 1.1 1997/07/31 23:13:14 curt
171 Revision 1.1 1997/05/29 00:09:56 curt
172 Initial Flight Gear revision.
174 * Revision 1.5 1994/01/11 18:47:05 bjax
175 * Changed include files to use types and constants, not ls_eom.h
176 * Also changed DATA type to SCALAR type.
178 * Revision 1.4 1993/12/14 21:06:47 bjax
179 * Removed global variable references Altitude and Latitude. EBJ
181 * Revision 1.3 1993/06/02 15:03:40 bjax
182 * Made new subroutine for calculating geodetic to geocentric; changed name
183 * of forward conversion routine from ls_geodesy to ls_geoc_to_geod.
186 ----------------------------------------------------------------------------
190 [ 1] Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
191 Control and Simulation", Wiley and Sons, 1992.
195 ----------------------------------------------------------------------------
199 ----------------------------------------------------------------------------
203 ----------------------------------------------------------------------------
206 lat_geoc Geocentric latitude, radians, + = North
207 radius C.G. radius to earth center, ft
209 ----------------------------------------------------------------------------
212 lat_geod Geodetic latitude, radians, + = North
213 alt C.G. altitude above mean sea level, ft
214 sea_level_r radius from earth center to sea level at
215 local vertical (surface normal) of C.G.
217 --------------------------------------------------------------------------*/
221 // Revision 1.2 1998/10/16 23:36:36 curt
224 // Revision 1.1 1998/10/16 19:30:40 curt
225 // Renamed .c -> .h so we can start adding c++ supporting routines.
227 // Revision 1.6 1998/07/08 14:40:07 curt
228 // polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
229 // Updated fg_geodesy comments to reflect that routines expect and produce
232 // Revision 1.5 1998/04/25 22:06:23 curt
233 // Edited cvs log messages in source files ... bad bad bad!
235 // Revision 1.4 1998/01/27 00:47:59 curt
236 // Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
237 // system and commandline/config file processing code.
239 // Revision 1.3 1998/01/19 19:27:12 curt
240 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
241 // This should simplify things tremendously.
243 // Revision 1.2 1997/12/15 23:54:54 curt
244 // Add xgl wrappers for debugging.
245 // Generate terrain normals on the fly.
247 // Revision 1.1 1997/07/31 23:13:14 curt