sgp4ext.cpp

NORAD公布的两行星历数据计算轨道参数模型

/*     ----------------------------------------------------------------
*
*                               sgp4ext.cpp
*
*    this file contains extra routines needed for the main test program for sgp4.
*    these routines are derived from the astro libraries.
*
*                            companion code for
*               fundamentals of astrodynamics and applications
*                                    2007
*                              by david vallado
*
*       (w) 719-573-2600, email [e-mail]
*
*    current :
*               2 apr 07  david vallado
*                           fix jday floor and str lengths
*                           updates for constants
*    changes :
*              14 aug 06  david vallado
*                           original baseline
*       ----------------------------------------------------------------      */

#include "sgp4ext.h"
#include "sgp4unit.h"

#define pi 3.14159265358979323846

double  sgn
        (
          double x
        )
   {
     if (x < 1.0)
       {
          return -1;
       }
       else if (x > 1.0)
       {
          return 1;
       }

    return 0.0;

   }  // end sgn

/* -----------------------------------------------------------------------------
*
*                           function mag
*
*  this procedure finds the magnitude of a vector.  the tolerance is set to
*    0.000001, thus the 1.0e-12 for the squared test of underflows.
*
*  author        : david vallado                  719-573-2600    1 mar 2001
*
*  inputs          description                    range / units
*    vec         - vector
*
*  outputs       :
*    vec         - answer stored in fourth component
*
*  locals        :
*    none.
*
*  coupling      :
*    none.
* --------------------------------------------------------------------------- */

double  mag
        (
          double x[3]
        )
   {
     return sqrt(x[0]*x[0] + x[1]*x[1] + x[2]*x[2]);
   }  // end mag

/* -----------------------------------------------------------------------------
*
*                           procedure cross
*
*  this procedure crosses two vectors.
*
*  author        : david vallado                  719-573-2600    1 mar 2001
*
*  inputs          description                    range / units
*    vec1        - vector number 1
*    vec2        - vector number 2
*
*  outputs       :
*    outvec      - vector result of a x b
*
*  locals        :
*    none.
*
*  coupling      :
*    mag           magnitude of a vector
 ---------------------------------------------------------------------------- */

void    cross
        (
          double vec1[3], double vec2[3], double outvec[3]
        )
   {
     outvec[0]= vec1[1]*vec2[2] - vec1[2]*vec2[1];
     outvec[1]= vec1[2]*vec2[0] - vec1[0]*vec2[2];
     outvec[2]= vec1[0]*vec2[1] - vec1[1]*vec2[0];
   }  // end cross


/* -----------------------------------------------------------------------------
*
*                           function dot
*
*  this function finds the dot product of two vectors.
*
*  author        : david vallado                  719-573-2600    1 mar 2001
*
*  inputs          description                    range / units
*    vec1        - vector number 1
*    vec2        - vector number 2
*
*  outputs       :
*    dot         - result
*
*  locals        :
*    none.
*
*  coupling      :
*    none.
*
* --------------------------------------------------------------------------- */

double  dot
        (
          double x[3], double y[3]
        )
   {
     return (x[0]*y[0] + x[1]*y[1] + x[2]*y[2]);
   }  // end dot

/* -----------------------------------------------------------------------------
*
*                           procedure angle
*
*  this procedure calculates the angle between two vectors.  the output is
*    set to 999999.1 to indicate an undefined value.  be sure to check for
*    this at the output phase.
*
*  author        : david vallado                  719-573-2600    1 mar 2001
*
*  inputs          description                    range / units
*    vec1        - vector number 1
*    vec2        - vector number 2
*
*  outputs       :
*    theta       - angle between the two vectors  -pi to pi
*
*  locals        :
*    temp        - temporary real variable
*
*  coupling      :
*    dot           dot product of two vectors
* --------------------------------------------------------------------------- */

double  angle
        (
          double vec1[3],
          double vec2[3]
        )
   {
     double small, undefined, magv1, magv2, temp;
     small     = 0.00000001;
     undefined = 999999.1;

     magv1 = mag(vec1);
     magv2 = mag(vec2);

     if (magv1*magv2 > small*small)
       {
         temp= dot(vec1,vec2) / (magv1*magv2);
         if (fabs( temp ) > 1.0)
             temp= sgn(temp) * 1.0;
         return acos( temp );
       }
       else
         return undefined;
   }  // end angle


/* -----------------------------------------------------------------------------
*
*                           function asinh
*
*  this function evaluates the inverse hyperbolic sine function.
*
*  author        : david vallado                  719-573-2600    1 mar 2001
*
*  inputs          description                    range / units
*    xval        - angle value                                  any real
*
*  outputs       :
*    arcsinh     - result                                       any real
*
*  locals        :
*    none.
*
*  coupling      :
*    none.
*
* --------------------------------------------------------------------------- */

double  asinh
        (
          double xval
        )
   {
     return log( xval + sqrt( xval*xval + 1.0 ) );
   }  // end asinh


/* -----------------------------------------------------------------------------
*
*                           function newtonnu
*
*  this function solves keplers equation when the true anomaly is known.
*    the mean and eccentric, parabolic, or hyperbolic anomaly is also found.
*    the parabolic limit at 168