200 lines
6.1 KiB
C
200 lines
6.1 KiB
C
/**************************************************************************
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* fg_geodesy.c -- routines to convert between geodetic and geocentric
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* coordinate systems.
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*
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* Copied and adapted directly from LaRCsim/ls_geodesy.c
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*
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* See below for the complete original LaRCsim comments.
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*
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* $Id$
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* (Log is kept at end of this file)
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**************************************************************************/
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#include <math.h>
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#include "fg_geodesy.h"
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#include "../constants.h"
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/* ONE_SECOND is pi/180/60/60, or about 100 feet at earths' equator */
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#define ONE_SECOND 4.848136811E-6
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/* fgGeocToGeod(lat_geoc, radius, *lat_geod, *alt, *sea_level_r)
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* INPUTS:
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* lat_geoc Geocentric latitude, radians, + = North
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* radius C.G. radius to earth center, ft
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*
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* OUTPUTS:
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* lat_geod Geodetic latitude, radians, + = North
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* alt C.G. altitude above mean sea level, ft
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* sea_level_r radius from earth center to sea level at
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* local vertical (surface normal) of C.G.
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*/
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void fgGeocToGeod( double lat_geoc, double radius, double
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*lat_geod, double *alt, double *sea_level_r )
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{
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double t_lat, x_alpha, mu_alpha, delt_mu, r_alpha, l_point, rho_alpha;
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double sin_mu_a, denom,delt_lambda, lambda_sl, sin_lambda_sl;
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if( ( (FG_PI_2 - lat_geoc) < ONE_SECOND ) /* near North pole */
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|| ( (FG_PI_2 + lat_geoc) < ONE_SECOND ) ) /* near South pole */
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{
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*lat_geod = lat_geoc;
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*sea_level_r = EQUATORIAL_RADIUS_KM*E;
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*alt = radius - *sea_level_r;
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} else {
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t_lat = tan(lat_geoc);
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x_alpha = E*EQUATORIAL_RADIUS_KM/sqrt(t_lat*t_lat + E*E);
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mu_alpha = atan2(sqrt(RESQ_KM - x_alpha*x_alpha),E*x_alpha);
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if (lat_geoc < 0) mu_alpha = - mu_alpha;
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sin_mu_a = sin(mu_alpha);
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delt_lambda = mu_alpha - lat_geoc;
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r_alpha = x_alpha/cos(lat_geoc);
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l_point = radius - r_alpha;
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*alt = l_point*cos(delt_lambda);
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denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a);
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rho_alpha = EQUATORIAL_RADIUS_KM*(1-EPS)/
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(denom*denom*denom);
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delt_mu = atan2(l_point*sin(delt_lambda),rho_alpha + *alt);
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*lat_geod = mu_alpha - delt_mu;
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lambda_sl = atan( E*E * tan(*lat_geod) ); /* SL geoc. latitude */
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sin_lambda_sl = sin( lambda_sl );
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*sea_level_r =
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sqrt(RESQ_KM / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
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}
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}
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/* fgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc )
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* INPUTS:
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* lat_geod Geodetic latitude, radians, + = North
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* alt C.G. altitude above mean sea level, ft
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*
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* OUTPUTS:
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* sl_radius SEA LEVEL radius to earth center, ft (add Altitude to
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* get true distance from earth center.
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* lat_geoc Geocentric latitude, radians, + = North
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*
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*/
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void fgGeodToGeoc( double lat_geod, double alt, double *sl_radius,
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double *lat_geoc )
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{
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double lambda_sl, sin_lambda_sl, cos_lambda_sl, sin_mu, cos_mu, px, py;
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lambda_sl = atan( E*E * tan(lat_geod) ); /* sea level geocentric latitude */
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sin_lambda_sl = sin( lambda_sl );
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cos_lambda_sl = cos( lambda_sl );
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sin_mu = sin(lat_geod); /* Geodetic (map makers') latitude */
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cos_mu = cos(lat_geod);
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*sl_radius =
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sqrt(RESQ_KM / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
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py = *sl_radius*sin_lambda_sl + alt*sin_mu;
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px = *sl_radius*cos_lambda_sl + alt*cos_mu;
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*lat_geoc = atan2( py, px );
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}
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/***************************************************************************
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TITLE: ls_geodesy
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----------------------------------------------------------------------------
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FUNCTION: Converts geocentric coordinates to geodetic positions
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----------------------------------------------------------------------------
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MODULE STATUS: developmental
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----------------------------------------------------------------------------
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GENEALOGY: Written as part of LaRCSim project by E. B. Jackson
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----------------------------------------------------------------------------
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DESIGNED BY: E. B. Jackson
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CODED BY: E. B. Jackson
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MAINTAINED BY: E. B. Jackson
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----------------------------------------------------------------------------
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MODIFICATION HISTORY:
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DATE PURPOSE BY
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930208 Modified to avoid singularity near polar region. EBJ
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930602 Moved backwards calcs here from ls_step. EBJ
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931214 Changed erroneous Latitude and Altitude variables to
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*lat_geod and *alt in routine ls_geoc_to_geod. EBJ
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940111 Changed header files from old ls_eom.h style to ls_types,
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and ls_constants. Also replaced old DATA type with new
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SCALAR type. EBJ
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CURRENT RCS HEADER:
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$Header$
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$Log$
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Revision 1.1 1997/07/31 23:13:14 curt
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Initial revision.
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Revision 1.1 1997/05/29 00:09:56 curt
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Initial Flight Gear revision.
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* Revision 1.5 1994/01/11 18:47:05 bjax
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* Changed include files to use types and constants, not ls_eom.h
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* Also changed DATA type to SCALAR type.
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*
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* Revision 1.4 1993/12/14 21:06:47 bjax
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* Removed global variable references Altitude and Latitude. EBJ
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*
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* Revision 1.3 1993/06/02 15:03:40 bjax
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* Made new subroutine for calculating geodetic to geocentric; changed name
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* of forward conversion routine from ls_geodesy to ls_geoc_to_geod.
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*
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----------------------------------------------------------------------------
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REFERENCES:
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[ 1] Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
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Control and Simulation", Wiley and Sons, 1992.
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ISBN 0-471-61397-5
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----------------------------------------------------------------------------
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CALLED BY: ls_aux
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----------------------------------------------------------------------------
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CALLS TO:
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----------------------------------------------------------------------------
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INPUTS:
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lat_geoc Geocentric latitude, radians, + = North
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radius C.G. radius to earth center, ft
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----------------------------------------------------------------------------
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OUTPUTS:
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lat_geod Geodetic latitude, radians, + = North
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alt C.G. altitude above mean sea level, ft
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sea_level_r radius from earth center to sea level at
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local vertical (surface normal) of C.G.
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--------------------------------------------------------------------------*/
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/* $Log$
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/* Revision 1.1 1997/07/31 23:13:14 curt
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/* Initial revision.
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/*
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*/
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