-/**************************************************************************
- * fg_geodesy.c -- 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 <math.h>
-
-#include <Include/fg_constants.h>
-
-#include "fg_geodesy.h"
-
-
-/* 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, 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.
- */
-
-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_KM*E;
- *alt = radius - *sea_level_r;
- } else {
- t_lat = tan(lat_geoc);
- x_alpha = E*EQUATORIAL_RADIUS_KM/sqrt(t_lat*t_lat + E*E);
- mu_alpha = atan2(sqrt(RESQ_KM - x_alpha*x_alpha),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);
- denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a);
- rho_alpha = EQUATORIAL_RADIUS_KM*(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_KM / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
- }
-}
-
-
-/* fgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc )
- * INPUTS:
- * lat_geod Geodetic latitude, radians, + = North
- * alt C.G. altitude above mean sea level, ft
- *
- * OUTPUTS:
- * sl_radius SEA LEVEL radius to earth center, ft (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_KM / (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 1.1 1998/04/08 23:21:11 curt
-Adopted Gnu automake/autoconf system.
-
-Revision 1.4 1998/01/27 00:47:59 curt
-Incorporated Paul Bleisch's <bleisch@chromatic.com> 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 <rpk@sgi.com>
-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 1.1 1998/04/08 23:21:11 curt
-/* Adopted Gnu automake/autoconf system.
-/*
- * Revision 1.4 1998/01/27 00:47:59 curt
- * Incorporated Paul Bleisch's <bleisch@chromatic.com> 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 <rpk@sgi.com>
- * 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.
- *
- */