// fg_geodesy.cxx -- routines to convert between geodetic and geocentric // coordinate systems. // // Copied and adapted directly from LaRCsim/ls_geodesy.c // // See below for the complete original LaRCsim comments. // // $Id$ // (Log is kept at end of this file) #include #include #include #include #include // ONE_SECOND is pi/180/60/60, or about 100 feet at earths' equator #define ONE_SECOND 4.848136811E-6 // fgGeocToGeod(lat_geoc, radius, *lat_geod, *alt, *sea_level_r) // INPUTS: // lat_geoc Geocentric latitude, radians, + = North // radius C.G. radius to earth center (meters) // // OUTPUTS: // lat_geod Geodetic latitude, radians, + = North // alt C.G. altitude above mean sea level (meters) // sea_level_r radius from earth center to sea level at // local vertical (surface normal) of C.G. (meters) void fgGeocToGeod( double lat_geoc, double radius, double *lat_geod, double *alt, double *sea_level_r ) { double t_lat, x_alpha, mu_alpha, delt_mu, r_alpha, l_point, rho_alpha; double sin_mu_a, denom,delt_lambda, lambda_sl, sin_lambda_sl; if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) // near North pole || ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) // near South pole { *lat_geod = lat_geoc; *sea_level_r = EQUATORIAL_RADIUS_M*E; *alt = radius - *sea_level_r; } else { t_lat = tan(lat_geoc); x_alpha = E*EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E); double tmp = RESQ_M - x_alpha * x_alpha; if ( tmp < 0.0 ) { tmp = 0.0; } mu_alpha = atan2(sqrt(tmp),E*x_alpha); if (lat_geoc < 0) mu_alpha = - mu_alpha; sin_mu_a = sin(mu_alpha); delt_lambda = mu_alpha - lat_geoc; r_alpha = x_alpha/cos(lat_geoc); l_point = radius - r_alpha; *alt = l_point*cos(delt_lambda); // check for domain error if ( errno == EDOM ) { cout << "Domain ERROR in fgGeocToGeod!!!!\n"; *alt = 0.0; } denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a); rho_alpha = EQUATORIAL_RADIUS_M*(1-EPS)/ (denom*denom*denom); delt_mu = atan2(l_point*sin(delt_lambda),rho_alpha + *alt); *lat_geod = mu_alpha - delt_mu; lambda_sl = atan( E*E * tan(*lat_geod) ); // SL geoc. latitude sin_lambda_sl = sin( lambda_sl ); *sea_level_r = sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl)); // check for domain error if ( errno == EDOM ) { cout << "Domain ERROR in fgGeocToGeod!!!!\n"; *sea_level_r = 0.0; } } } // fgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc ) // INPUTS: // lat_geod Geodetic latitude, radians, + = North // alt C.G. altitude above mean sea level (meters) // // OUTPUTS: // sl_radius SEA LEVEL radius to earth center (meters) // (add Altitude to get true distance from earth center. // lat_geoc Geocentric latitude, radians, + = North // void fgGeodToGeoc( double lat_geod, double alt, double *sl_radius, double *lat_geoc ) { double lambda_sl, sin_lambda_sl, cos_lambda_sl, sin_mu, cos_mu, px, py; lambda_sl = atan( E*E * tan(lat_geod) ); // sea level geocentric latitude sin_lambda_sl = sin( lambda_sl ); cos_lambda_sl = cos( lambda_sl ); sin_mu = sin(lat_geod); // Geodetic (map makers') latitude cos_mu = cos(lat_geod); *sl_radius = sqrt(RESQ_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl)); py = *sl_radius*sin_lambda_sl + alt*sin_mu; px = *sl_radius*cos_lambda_sl + alt*cos_mu; *lat_geoc = atan2( py, px ); } /*************************************************************************** TITLE: ls_geodesy ---------------------------------------------------------------------------- FUNCTION: Converts geocentric coordinates to geodetic positions ---------------------------------------------------------------------------- MODULE STATUS: developmental ---------------------------------------------------------------------------- GENEALOGY: Written as part of LaRCSim project by E. B. Jackson ---------------------------------------------------------------------------- DESIGNED BY: E. B. Jackson CODED BY: E. B. Jackson MAINTAINED BY: E. B. Jackson ---------------------------------------------------------------------------- MODIFICATION HISTORY: DATE PURPOSE BY 930208 Modified to avoid singularity near polar region. EBJ 930602 Moved backwards calcs here from ls_step. EBJ 931214 Changed erroneous Latitude and Altitude variables to *lat_geod and *alt in routine ls_geoc_to_geod. EBJ 940111 Changed header files from old ls_eom.h style to ls_types, and ls_constants. Also replaced old DATA type with new SCALAR type. EBJ CURRENT RCS HEADER: $Header$ $Log$ Revision 1.4 1998/11/20 01:00:36 curt Patch in fgGeoc2Geod() to avoid a floating explosion. point3d.hxx include math.h for FreeBSD Revision 1.3 1998/11/11 00:18:36 curt Check for domain error in fgGeoctoGeod() Revision 1.2 1998/10/16 23:36:36 curt c++-ifying. Revision 1.1 1998/10/16 19:30:40 curt Renamed .c -> .h so we can start adding c++ supporting routines. Revision 1.6 1998/07/08 14:40:07 curt polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx Updated fg_geodesy comments to reflect that routines expect and produce meters. Revision 1.5 1998/04/25 22:06:23 curt Edited cvs log messages in source files ... bad bad bad! Revision 1.4 1998/01/27 00:47:59 curt Incorporated Paul Bleisch's new debug message system and commandline/config file processing code. Revision 1.3 1998/01/19 19:27:12 curt Merged in make system changes from Bob Kuehne This should simplify things tremendously. Revision 1.2 1997/12/15 23:54:54 curt Add xgl wrappers for debugging. Generate terrain normals on the fly. Revision 1.1 1997/07/31 23:13:14 curt Initial revision. Revision 1.1 1997/05/29 00:09:56 curt Initial Flight Gear revision. * Revision 1.5 1994/01/11 18:47:05 bjax * Changed include files to use types and constants, not ls_eom.h * Also changed DATA type to SCALAR type. * * Revision 1.4 1993/12/14 21:06:47 bjax * Removed global variable references Altitude and Latitude. EBJ * * Revision 1.3 1993/06/02 15:03:40 bjax * Made new subroutine for calculating geodetic to geocentric; changed name * of forward conversion routine from ls_geodesy to ls_geoc_to_geod. * ---------------------------------------------------------------------------- REFERENCES: [ 1] Stevens, Brian L.; and Lewis, Frank L.: "Aircraft Control and Simulation", Wiley and Sons, 1992. ISBN 0-471-61397-5 ---------------------------------------------------------------------------- CALLED BY: ls_aux ---------------------------------------------------------------------------- CALLS TO: ---------------------------------------------------------------------------- INPUTS: lat_geoc Geocentric latitude, radians, + = North radius C.G. radius to earth center, ft ---------------------------------------------------------------------------- OUTPUTS: lat_geod Geodetic latitude, radians, + = North alt C.G. altitude above mean sea level, ft sea_level_r radius from earth center to sea level at local vertical (surface normal) of C.G. --------------------------------------------------------------------------*/ // $Log$ // Revision 1.4 1998/11/20 01:00:36 curt // Patch in fgGeoc2Geod() to avoid a floating explosion. // point3d.hxx include math.h for FreeBSD // // Revision 1.3 1998/11/11 00:18:36 curt // Check for domain error in fgGeoctoGeod() // // Revision 1.2 1998/10/16 23:36:36 curt // c++-ifying. // // Revision 1.1 1998/10/16 19:30:40 curt // Renamed .c -> .h so we can start adding c++ supporting routines. // // Revision 1.6 1998/07/08 14:40:07 curt // polar3d.[ch] renamed to polar3d.[ch]xx, vector.[ch] renamed to vector.[ch]xx // Updated fg_geodesy comments to reflect that routines expect and produce // meters. // // Revision 1.5 1998/04/25 22:06:23 curt // Edited cvs log messages in source files ... bad bad bad! // // Revision 1.4 1998/01/27 00:47:59 curt // Incorporated Paul Bleisch's new debug message // system and commandline/config file processing code. // // Revision 1.3 1998/01/19 19:27:12 curt // Merged in make system changes from Bob Kuehne // This should simplify things tremendously. // // Revision 1.2 1997/12/15 23:54:54 curt // Add xgl wrappers for debugging. // Generate terrain normals on the fly. // // Revision 1.1 1997/07/31 23:13:14 curt // Initial revision. //