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)
15 #include <Include/fg_constants.h>
16 #include <Math/fg_geodesy.hxx>
17 #include <Math/point3d.hxx>
20 // ONE_SECOND is pi/180/60/60, or about 100 feet at earths' equator
21 #define ONE_SECOND 4.848136811E-6
24 // fgGeocToGeod(lat_geoc, radius, *lat_geod, *alt, *sea_level_r)
26 // lat_geoc Geocentric latitude, radians, + = North
27 // radius C.G. radius to earth center (meters)
30 // lat_geod Geodetic latitude, radians, + = North
31 // alt C.G. altitude above mean sea level (meters)
32 // sea_level_r radius from earth center to sea level at
33 // local vertical (surface normal) of C.G. (meters)
36 void fgGeocToGeod( double lat_geoc, double radius, double
37 *lat_geod, double *alt, double *sea_level_r )
39 double t_lat, x_alpha, mu_alpha, delt_mu, r_alpha, l_point, rho_alpha;
40 double sin_mu_a, denom,delt_lambda, lambda_sl, sin_lambda_sl;
42 if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) // near North pole
43 || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) // near South pole
46 *sea_level_r = EQUATORIAL_RADIUS_M*E;
47 *alt = radius - *sea_level_r;
49 t_lat = tan(lat_geoc);
50 x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
51 double tmp = RESQ_M - x_alpha * x_alpha;
52 if ( tmp < 0.0 ) { tmp = 0.0; }
53 mu_alpha = atan2(sqrt(tmp),E*x_alpha);
54 if (lat_geoc < 0) mu_alpha = - mu_alpha;
55 sin_mu_a = sin(mu_alpha);
56 delt_lambda = mu_alpha - lat_geoc;
57 r_alpha = x_alpha/cos(lat_geoc);
58 l_point = radius - r_alpha;
59 *alt = l_point*cos(delt_lambda);
61 // check for domain error
62 if ( errno == EDOM ) {
63 cout << "Domain ERROR in fgGeocToGeod!!!!\n";
67 denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a);
68 rho_alpha = EQUATORIAL_RADIUS_M*(1-EPS)/
70 delt_mu = atan2(l_point*sin(delt_lambda),rho_alpha + *alt);
71 *lat_geod = mu_alpha - delt_mu;
72 lambda_sl = atan( E*E * tan(*lat_geod) ); // SL geoc. latitude
73 sin_lambda_sl = sin( lambda_sl );
75 sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
77 // check for domain error
78 if ( errno == EDOM ) {
79 cout << "Domain ERROR in fgGeocToGeod!!!!\n";
87 // fgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc )
89 // lat_geod Geodetic latitude, radians, + = North
90 // alt C.G. altitude above mean sea level (meters)
93 // sl_radius SEA LEVEL radius to earth center (meters)
94 // (add Altitude to get true distance from earth center.
95 // lat_geoc Geocentric latitude, radians, + = North
99 void fgGeodToGeoc( double lat_geod, double alt, double *sl_radius,
102 double lambda_sl, sin_lambda_sl, cos_lambda_sl, sin_mu, cos_mu, px, py;
104 lambda_sl = atan( E*E * tan(lat_geod) ); // sea level geocentric latitude
105 sin_lambda_sl = sin( lambda_sl );
106 cos_lambda_sl = cos( lambda_sl );
107 sin_mu = sin(lat_geod); // Geodetic (map makers') latitude
108 cos_mu = cos(lat_geod);
110 sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
111 py = *sl_radius*sin_lambda_sl + alt*sin_mu;
112 px = *sl_radius*cos_lambda_sl + alt*cos_mu;
113 *lat_geoc = atan2( py, px );
117 /***************************************************************************
121 ----------------------------------------------------------------------------
123 FUNCTION: Converts geocentric coordinates to geodetic positions
125 ----------------------------------------------------------------------------
127 MODULE STATUS: developmental
129 ----------------------------------------------------------------------------
131 GENEALOGY: Written as part of LaRCSim project by E. B. Jackson
133 ----------------------------------------------------------------------------
135 DESIGNED BY: E. B. Jackson
137 CODED BY: E. B. Jackson
139 MAINTAINED BY: E. B. Jackson
141 ----------------------------------------------------------------------------
143 MODIFICATION HISTORY:
147 930208 Modified to avoid singularity near polar region. EBJ
148 930602 Moved backwards calcs here from ls_step. EBJ
149 931214 Changed erroneous Latitude and Altitude variables to
150 *lat_geod and *alt in routine ls_geoc_to_geod. EBJ
151 940111 Changed header files from old ls_eom.h style to ls_types,
152 and ls_constants. Also replaced old DATA type with new
159 Revision 1.4 1998/11/20 01:00:36 curt
160 Patch in fgGeoc2Geod() to avoid a floating explosion.
161 point3d.hxx include math.h for FreeBSD
163 Revision 1.3 1998/11/11 00:18:36 curt
164 Check for domain error in fgGeoctoGeod()
166 Revision 1.2 1998/10/16 23:36:36 curt
169 Revision 1.1 1998/10/16 19:30:40 curt
170 Renamed .c -> .h so we can start adding c++ supporting routines.
172 Revision 1.6 1998/07/08 14:40:07 curt
173 polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
174 Updated fg_geodesy comments to reflect that routines expect and produce
177 Revision 1.5 1998/04/25 22:06:23 curt
178 Edited cvs log messages in source files ... bad bad bad!
180 Revision 1.4 1998/01/27 00:47:59 curt
181 Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
182 system and commandline/config file processing code.
184 Revision 1.3 1998/01/19 19:27:12 curt
185 Merged in make system changes from Bob Kuehne <rpk@sgi.com>
186 This should simplify things tremendously.
188 Revision 1.2 1997/12/15 23:54:54 curt
189 Add xgl wrappers for debugging.
190 Generate terrain normals on the fly.
192 Revision 1.1 1997/07/31 23:13:14 curt
195 Revision 1.1 1997/05/29 00:09:56 curt
196 Initial Flight Gear revision.
198 * Revision 1.5 1994/01/11 18:47:05 bjax
199 * Changed include files to use types and constants, not ls_eom.h
200 * Also changed DATA type to SCALAR type.
202 * Revision 1.4 1993/12/14 21:06:47 bjax
203 * Removed global variable references Altitude and Latitude. EBJ
205 * Revision 1.3 1993/06/02 15:03:40 bjax
206 * Made new subroutine for calculating geodetic to geocentric; changed name
207 * of forward conversion routine from ls_geodesy to ls_geoc_to_geod.
210 ----------------------------------------------------------------------------
214 [ 1] Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
215 Control and Simulation", Wiley and Sons, 1992.
219 ----------------------------------------------------------------------------
223 ----------------------------------------------------------------------------
227 ----------------------------------------------------------------------------
230 lat_geoc Geocentric latitude, radians, + = North
231 radius C.G. radius to earth center, ft
233 ----------------------------------------------------------------------------
236 lat_geod Geodetic latitude, radians, + = North
237 alt C.G. altitude above mean sea level, ft
238 sea_level_r radius from earth center to sea level at
239 local vertical (surface normal) of C.G.
241 --------------------------------------------------------------------------*/
245 // Revision 1.4 1998/11/20 01:00:36 curt
246 // Patch in fgGeoc2Geod() to avoid a floating explosion.
247 // point3d.hxx include math.h for FreeBSD
249 // Revision 1.3 1998/11/11 00:18:36 curt
250 // Check for domain error in fgGeoctoGeod()
252 // Revision 1.2 1998/10/16 23:36:36 curt
255 // Revision 1.1 1998/10/16 19:30:40 curt
256 // Renamed .c -> .h so we can start adding c++ supporting routines.
258 // Revision 1.6 1998/07/08 14:40:07 curt
259 // polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx
260 // Updated fg_geodesy comments to reflect that routines expect and produce
263 // Revision 1.5 1998/04/25 22:06:23 curt
264 // Edited cvs log messages in source files ... bad bad bad!
266 // Revision 1.4 1998/01/27 00:47:59 curt
267 // Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
268 // system and commandline/config file processing code.
270 // Revision 1.3 1998/01/19 19:27:12 curt
271 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
272 // This should simplify things tremendously.
274 // Revision 1.2 1997/12/15 23:54:54 curt
275 // Add xgl wrappers for debugging.
276 // Generate terrain normals on the fly.
278 // Revision 1.1 1997/07/31 23:13:14 curt