-// sg_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.
-//
-// $Id$
-#include <simgear/compiler.h>
-
-#ifdef SG_HAVE_STD_INCLUDES
-# include <cmath>
-# include <cerrno>
-# include <cstdio>
-#else
-# include <math.h>
-# include <errno.h>
-# include <stdio.h>
+#ifdef HAVE_CONFIG_H
+# include <simgear_config.h>
#endif
#include <simgear/constants.h>
-#include <simgear/debug/logstream.hxx>
-
-#include "point3d.hxx"
+#include "SGMath.hxx"
#include "sg_geodesy.hxx"
-#include "localconsts.hxx"
-
-
-SG_USING_STD(cout);
-
-
-// #define DOMAIN_ERR_DEBUG 1
-
-// sgGeocToGeod(lat_geoc, radius, *lat_geod, *alt, *sea_level_r)
-// INPUTS:
-// lat_geoc Geocentric latitude, radians, + = North
-// radius C.G. radius to earth center (meters)
+// Notes:
//
-// 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 sgGeocToGeod( const double& lat_geoc, const double& radius,
- double *lat_geod, double *alt, double *sea_level_r )
-{
-#ifdef DOMAIN_ERR_DEBUG
- errno = 0; // start with error zero'd
-#endif
-
- 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( ( (SGD_PI_2 - lat_geoc) < SG_ONE_SECOND ) // near North pole
- || ( (SGD_PI_2 + lat_geoc) < SG_ONE_SECOND ) ) // near South pole
- {
- *lat_geod = lat_geoc;
- *sea_level_r = SG_EQUATORIAL_RADIUS_M*E;
- *alt = radius - *sea_level_r;
- } else {
- // cout << " lat_geoc = " << lat_geoc << endl;
- t_lat = tan(lat_geoc);
- // cout << " tan(t_lat) = " << t_lat << endl;
- x_alpha = E*SG_EQUATORIAL_RADIUS_M/sqrt(t_lat*t_lat + E*E);
-#ifdef DOMAIN_ERR_DEBUG
- if ( errno ) {
- perror("fgGeocToGeod()");
- SG_LOG( SG_GENERAL, SG_ALERT, "sqrt(" << t_lat*t_lat + E*E << ")" );
- }
-#endif
- // cout << " x_alpha = " << x_alpha << endl;
- double tmp = sqrt(SG_EQ_RAD_SQUARE_M - x_alpha * x_alpha);
- if ( tmp < 0.0 ) { tmp = 0.0; }
-#ifdef DOMAIN_ERR_DEBUG
- if ( errno ) {
- perror("fgGeocToGeod()");
- SG_LOG( SG_GENERAL, SG_ALERT, "sqrt(" << SG_EQ_RAD_SQUARE_M - x_alpha * x_alpha
- << ")" );
- }
-#endif
- mu_alpha = atan2(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);
-
- denom = sqrt(1-EPS*EPS*sin_mu_a*sin_mu_a);
-#ifdef DOMAIN_ERR_DEBUG
- if ( errno ) {
- perror("fgGeocToGeod()");
- SG_LOG( SG_GENERAL, SG_ALERT, "sqrt(" <<
- 1-EPS*EPS*sin_mu_a*sin_mu_a << ")" );
- }
-#endif
- rho_alpha = SG_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(SG_EQ_RAD_SQUARE_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
-#ifdef DOMAIN_ERR_DEBUG
- if ( errno ) {
- perror("fgGeocToGeod()");
- SG_LOG( SG_GENERAL, SG_ALERT, "sqrt(" <<
- SG_EQ_RAD_SQUARE_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl)
- << ")" );
- }
-#endif
-
- }
-
-}
-
-
-// sgGeodToGeoc( lat_geod, alt, *sl_radius, *lat_geoc )
-// INPUTS:
-// lat_geod Geodetic latitude, radians, + = North
-// alt C.G. altitude above mean sea level (meters)
+// The XYZ/cartesian coordinate system in use puts the X axis through
+// zero lat/lon (off west Africa), the Z axis through the north pole,
+// and the Y axis through 90 degrees longitude (in the Indian Ocean).
//
-// 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
+// All latitude and longitude values are in radians. Altitude is in
+// meters, with zero on the WGS84 ellipsoid.
//
-
-
-void sgGeodToGeoc( const double& lat_geod, const double& alt, double *sl_radius,
- double *lat_geoc )
-{
- double lambda_sl, sin_lambda_sl, cos_lambda_sl, sin_mu, cos_mu, px, py;
-
-#ifdef DOMAIN_ERR_DEBUG
- errno = 0;
-#endif
-
- 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(SG_EQ_RAD_SQUARE_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl));
-#ifdef DOMAIN_ERR_DEBUG
- if ( errno ) {
- perror("fgGeodToGeoc()");
- SG_LOG( SG_GENERAL, SG_ALERT, "sqrt(" <<
- SG_EQ_RAD_SQUARE_M / (1 + ((1/(E*E))-1)*sin_lambda_sl*sin_lambda_sl)
- << ")" );
- }
+// The code below makes use of the notion of "squashed" space. This
+// is a 2D cylindrical coordinate system where the radius from the Z
+// axis is multiplied by SQUASH; the earth in this space is a perfect
+// circle with a radius of POLRAD.
+//
+// Performance: with full optimization, a transformation from
+// lat/lon/alt to XYZ and back takes 5263 CPU cycles on my 2.2GHz
+// Pentium 4. About 83% of this is spent in the iterative sgCartToGeod()
+// algorithm.
+
+// These are hard numbers from the WGS84 standard. DON'T MODIFY
+// unless you want to change the datum.
+static const double EQURAD = 6378137;
+static const double iFLATTENING = 298.257223563;
+
+// These are derived quantities more useful to the code:
+#if 0
+static const double SQUASH = 1 - 1/iFLATTENING;
+static const double STRETCH = 1/SQUASH;
+static const double POLRAD = EQURAD * SQUASH;
+#else
+// High-precision versions of the above produced with an arbitrary
+// precision calculator (the compiler might lose a few bits in the FPU
+// operations). These are specified to 81 bits of mantissa, which is
+// higher than any FPU known to me:
+static const double SQUASH = 0.9966471893352525192801545;
+static const double STRETCH = 1.0033640898209764189003079;
+static const double POLRAD = 6356752.3142451794975639668;
#endif
- py = *sl_radius*sin_lambda_sl + alt*sin_mu;
- px = *sl_radius*cos_lambda_sl + alt*cos_mu;
- *lat_geoc = atan2( py, px );
-}
-
+////////////////////////////////////////////////////////////////////////
+//
// Direct and inverse distance functions
//
// Proceedings of the 7th International Symposium on Geodetic
//
// modified for FlightGear to use WGS84 only -- Norman Vine
-#define GEOD_INV_PI SGD_PI
+static const double GEOD_INV_PI = SGD_PI;
// s == distance
// az = azimuth
-// for WGS_84 a = 6378137.000, rf = 298.257223563;
-
static inline double M0( double e2 ) {
//double e4 = e2*e2;
return GEOD_INV_PI*(1.0 - e2*( 1.0/4.0 + e2*( 3.0/64.0 +
}
-// given, alt, lat1, lon1, az1 and distance (s), calculate lat2, lon2
+// given, lat1, lon1, az1 and distance (s), calculate lat2, lon2
// and az2. Lat, lon, and azimuth are in degrees. distance in meters
-int geo_direct_wgs_84 ( const double& alt, const double& lat1,
- const double& lon1, const double& az1,
- const double& s, double *lat2, double *lon2,
+int geo_direct_wgs_84 ( double lat1, double lon1, double az1,
+ double s, double *lat2, double *lon2,
double *az2 )
{
- double a = 6378137.000, rf = 298.257223563;
+ double a = EQURAD, rf = iFLATTENING;
double RADDEG = (GEOD_INV_PI)/180.0, testv = 1.0E-10;
double f = ( rf > 0.0 ? 1.0/rf : 0.0 );
double b = a*(1.0-f);
double dM = a*M0(e2) - s;
double paz = ( phi1 < 0.0 ? 180.0 : 0.0 );
double zero = 0.0f;
- return geo_direct_wgs_84( alt, zero, lon1, paz, dM, lat2, lon2, az2 );
+ return geo_direct_wgs_84( zero, lon1, paz, dM, lat2, lon2, az2 );
}
}
-// given alt, lat1, lon1, lat2, lon2, calculate starting and ending
+// given lat1, lon1, lat2, lon2, calculate starting and ending
// az1, az2 and distance (s). Lat, lon, and azimuth are in degrees.
// distance in meters
-int geo_inverse_wgs_84( const double& alt, const double& lat1,
- const double& lon1, const double& lat2,
- const double& lon2, double *az1, double *az2,
+int geo_inverse_wgs_84( double lat1, double lon1, double lat2,
+ double lon2, double *az1, double *az2,
double *s )
{
- double a = 6378137.000, rf = 298.257223563;
+ double a = EQURAD, rf = iFLATTENING;
int iter=0;
double RADDEG = (GEOD_INV_PI)/180.0, testv = 1.0E-10;
double f = ( rf > 0.0 ? 1.0/rf : 0.0 );
return 0;
} else if( fabs(cosphi1) < testv ) {
// initial point is polar
- int k = geo_inverse_wgs_84( alt, lat2,lon2,lat1,lon1, az1,az2,s );
+ int k = geo_inverse_wgs_84( lat2,lon2,lat1,lon1, az1,az2,s );
k = k; // avoid compiler error since return result is unused
b = *az1; *az1 = *az2; *az2 = b;
return 0;
} else if( fabs(cosphi2) < testv ) {
// terminal point is polar
double _lon1 = lon1 + 180.0f;
- int k = geo_inverse_wgs_84( alt, lat1, lon1, lat1, _lon1,
+ int k = geo_inverse_wgs_84( lat1, lon1, lat1, _lon1,
az1, az2, s );
k = k; // avoid compiler error since return result is unused
*s /= 2.0;
{
// Geodesic passes through the pole (antipodal)
double s1,s2;
- geo_inverse_wgs_84( alt, lat1,lon1, lat1,lon2, az1,az2, &s1 );
- geo_inverse_wgs_84( alt, lat2,lon2, lat1,lon2, az1,az2, &s2 );
+ geo_inverse_wgs_84( lat1,lon1, lat1,lon2, az1,az2, &s1 );
+ geo_inverse_wgs_84( lat2,lon2, lat1,lon2, az1,az2, &s2 );
*az2 = *az1;
*s = s1 + s2;
return 0;
return 0;
}
}
-
-
-/***************************************************************************
-
- 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:
-
-$Header$
- * 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.
-
---------------------------------------------------------------------------*/
-
-
projects / simgear.git / blobdiff