void
Calculate_Obs(double _time,
vector_t *pos,
vector_t *vel,
geodetic_t *geodetic,
obs_set_t *obs_set)
{
double
sin_lat,cos_lat,
sin_theta,cos_theta,
el,azim,
top_s,top_e,top_z;
vector_t
obs_pos,obs_vel,range,rgvel;
Calculate_User_PosVel(_time, geodetic, &obs_pos, &obs_vel);
range.x = pos->x - obs_pos.x;
range.y = pos->y - obs_pos.y;
range.z = pos->z - obs_pos.z;
rgvel.x = vel->x - obs_vel.x;
rgvel.y = vel->y - obs_vel.y;
rgvel.z = vel->z - obs_vel.z;
Magnitude(&range);
sin_lat = sin(geodetic->lat);
cos_lat = cos(geodetic->lat);
sin_theta = sin(geodetic->theta);
cos_theta = cos(geodetic->theta);
top_s = sin_lat * cos_theta * range.x
+ sin_lat * sin_theta * range.y
- cos_lat * range.z;
top_e = -sin_theta * range.x
+ cos_theta * range.y;
top_z = cos_lat * cos_theta * range.x
+ cos_lat * sin_theta * range.y
+ sin_lat * range.z;
azim = atan(-top_e/top_s); /*Azimuth*/
if( top_s > 0 )
azim = azim + pi;
if( azim < 0 )
azim = azim + twopi;
el = ArcSin(top_z/range.w);
obs_set->az = azim; /* Azimuth (radians) */
obs_set->el = el; /* Elevation (radians)*/
obs_set->range = range.w; /* Range (kilometers) */
/* Range Rate (kilometers/second)*/
obs_set->range_rate = Dot(&range, &rgvel)/range.w;
/* Corrections for atmospheric refraction */
/* Reference: Astronomical Algorithms by Jean Meeus, pp. 101-104 */
/* Correction is meaningless when apparent elevation is below horizon */
// obs_set->el = obs_set->el + Radians((1.02/tan(Radians(Degrees(el)+
// 10.3/(Degrees(el)+5.11))))/60);
if( obs_set->el >= 0 )
SetFlag(VISIBLE_FLAG);
else
{
obs_set->el = el; /*Reset to true elevation*/
ClearFlag(VISIBLE_FLAG);
} /*else*/
} /*Procedure Calculate_Obs*/
void Calculate_Obs(double time, const double pos[3], const double vel[3], geodetic_t *geodetic, vector_t *obs_set)
{
/* The procedures Calculate_Obs and Calculate_RADec calculate */
/* the *topocentric* coordinates of the object with ECI position, */
/* {pos}, and velocity, {vel}, from location {geodetic} at {time}. */
/* The {obs_set} returned for Calculate_Obs consists of azimuth, */
/* elevation, range, and range rate (in that order) with units of */
/* radians, radians, kilometers, and kilometers/second, respectively. */
/* The WGS '72 geoid is used and the effect of atmospheric refraction */
/* (under standard temperature and pressure) is incorporated into the */
/* elevation calculation; the effect of atmospheric refraction on */
/* range and range rate has not yet been quantified. */
/* The {obs_set} for Calculate_RADec consists of right ascension and */
/* declination (in that order) in radians. Again, calculations are */
/* based on *topocentric* position using the WGS '72 geoid and */
/* incorporating atmospheric refraction. */
double sin_lat, cos_lat, sin_theta, cos_theta, el, azim, top_s, top_e, top_z;
double obs_pos[3];
double obs_vel[3];
double range[3];
double rgvel[3];
Calculate_User_PosVel(time, geodetic, obs_pos, obs_vel);
vec3_sub(pos, obs_pos, range);
vec3_sub(vel, obs_vel, rgvel);
double range_length = vec3_length(range);
sin_lat=sin(geodetic->lat);
cos_lat=cos(geodetic->lat);
sin_theta=sin(geodetic->theta);
cos_theta=cos(geodetic->theta);
top_s=sin_lat*cos_theta*range[0]+sin_lat*sin_theta*range[1]-cos_lat*range[2];
top_e=-sin_theta*range[0]+cos_theta*range[1];
top_z=cos_lat*cos_theta*range[0]+cos_lat*sin_theta*range[1]+sin_lat*range[2];
azim=atan(-top_e/top_s); /* Azimuth */
if (top_s>0.0)
azim=azim+pi;
if (azim<0.0)
azim = azim + 2*M_PI;
el=ArcSin(top_z/range_length);
obs_set->x=azim; /* Azimuth (radians) */
obs_set->y=el; /* Elevation (radians) */
obs_set->z=range_length; /* Range (kilometers) */
/* Range Rate (kilometers/second) */
obs_set->w = vec3_dot(range, rgvel)/vec3_length(range);
obs_set->y=el;
/**** End bypass ****/
if (obs_set->y<0.0)
obs_set->y=el; /* Reset to true elevation */
}
