158 lines
4.9 KiB
C
158 lines
4.9 KiB
C
/***************************************************************************
|
|
|
|
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 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.
|
|
|
|
--------------------------------------------------------------------------*/
|
|
|
|
#include "ls_types.h"
|
|
#include "ls_constants.h"
|
|
#include <math.h>
|
|
|
|
/* ONE_SECOND is pi/180/60/60, or about 100 feet at earths' equator */
|
|
#define ONE_SECOND 4.848136811E-6
|
|
#define HALF_PI 0.5*PI
|
|
|
|
|
|
void ls_geoc_to_geod( lat_geoc, radius, lat_geod, alt, sea_level_r )
|
|
SCALAR lat_geoc;
|
|
SCALAR radius;
|
|
SCALAR *lat_geod;
|
|
SCALAR *alt;
|
|
SCALAR *sea_level_r;
|
|
{
|
|
SCALAR t_lat, x_alpha, mu_alpha, delt_mu, r_alpha, l_point, rho_alpha;
|
|
SCALAR sin_mu_a, denom,delt_lambda, lambda_sl, sin_lambda_sl;
|
|
|
|
if( ( (HALF_PI - lat_geoc) < ONE_SECOND ) /* near North pole */
|
|
|| ( (HALF_PI + lat_geoc) < ONE_SECOND ) ) /* near South pole */
|
|
{
|
|
*lat_geod = lat_geoc;
|
|
*sea_level_r = EQUATORIAL_RADIUS*E;
|
|
*alt = radius - *sea_level_r;
|
|
}
|
|
else
|
|
{
|
|
t_lat = tan(lat_geoc);
|
|
x_alpha = E*EQUATORIAL_RADIUS/sqrt(t_lat*t_lat + E*E);
|
|
mu_alpha = atan2(sqrt(RESQ - 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*(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
|
|
/(1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
|
|
}
|
|
}
|
|
|
|
void ls_geod_to_geoc( lat_geod, alt, sl_radius, lat_geoc )
|
|
SCALAR lat_geod;
|
|
SCALAR alt;
|
|
SCALAR *sl_radius;
|
|
SCALAR *lat_geoc;
|
|
{
|
|
SCALAR 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
|
|
/(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 );
|
|
}
|