<?php
/**
* An example of looking up the lat/lon of the sun for putting on a map.
* "dark" lat/lon is the anti-solar point, useful for drawing a
* "solar terminator"
*/
// No autoloading here, require needed files
require_once 'Predict/Solar.php';
require_once 'Predict/SGPObs.php';
require_once 'Predict/Math.php';
require_once 'Predict/Time.php';
// Set up data constructs
$solar_vector = new Predict_Vector();
$solar_geodetic = new Predict_Geodetic();
// Use current time in the form of a daynum
$time = time();
$daynum = Predict_Time::unix2daynum($time);
// Do calculations
Predict_Solar::Calculate_Solar_Position($daynum, $solar_vector);
Predict_SGPObs::Calculate_LatLonAlt($daynum, $solar_vector, $solar_geodetic);
// Format to degrees
$solar_lat = Predict_Math::Degrees($solar_geodetic->lat);
$solar_lon = Predict_Math::Degrees($solar_geodetic->lon);
// Reverse values for night circle center
$dark_lat = -$solar_lat;
$dark_lon = -$solar_lon;
$output = array('solar_lat' => $solar_lat, 'solar_lon' => $solar_lon, 'dark_lat' => $dark_lat, 'dark_lon' => $dark_lon, 'timestamp' => $time);
// output results
var_dump(json_encode($output));
/**
* Finds the current location of the sun based on the observer location
*
* @param Predict_QTH $qth The observer location
* @param int $daynum The daynum or null to use the current daynum
*
* @return Predict_ObsSet
*/
public static function FindSun(Predict_QTH $qth, $daynum = null)
{
if ($daynum === null) {
$daynum = Predict_Time::get_current_daynum();
}
$obs_geodetic = new Predict_Geodetic();
$obs_geodetic->lon = $qth->lon * Predict::de2ra;
$obs_geodetic->lat = $qth->lat * Predict::de2ra;
$obs_geodetic->alt = $qth->alt / 1000.0;
$obs_geodetic->theta = 0;
$solar_vector = new Predict_Vector();
$zero_vector = new Predict_Vector();
$solar_set = new Predict_ObsSet();
self::Calculate_Solar_Position($daynum, $solar_vector);
Predict_SGPObs::Calculate_Obs($daynum, $solar_vector, $zero_vector, $obs_geodetic, $solar_set);
$solar_set->az = Predict_Math::Degrees($solar_set->az);
$solar_set->el = Predict_Math::Degrees($solar_set->el);
return $solar_set;
}
/** SGP4SDP4 driver for doing AOS/LOS calculations.
* @param Predict_Sat $sat The satellite data.
* @param Predict_QTH $qth The QTH observer location data.
* @param float $t The time for calculation (Julian Date)
*
*/
public function predict_calc(Predict_Sat $sat, Predict_QTH $qth, $t)
{
$obs_set = new Predict_ObsSet();
$sat_geodetic = new Predict_Geodetic();
$obs_geodetic = new Predict_Geodetic();
$obs_geodetic->lon = $qth->lon * self::de2ra;
$obs_geodetic->lat = $qth->lat * self::de2ra;
$obs_geodetic->alt = $qth->alt / 1000.0;
$obs_geodetic->theta = 0;
$sat->jul_utc = $t;
$sat->tsince = ($sat->jul_utc - $sat->jul_epoch) * self::xmnpda;
/* call the norad routines according to the deep-space flag */
$sgpsdp = Predict_SGPSDP::getInstance($sat);
if ($sat->flags & Predict_SGPSDP::DEEP_SPACE_EPHEM_FLAG) {
$sgpsdp->SDP4($sat, $sat->tsince);
} else {
$sgpsdp->SGP4($sat, $sat->tsince);
}
Predict_Math::Convert_Sat_State($sat->pos, $sat->vel);
/* get the velocity of the satellite */
$sat->vel->w = sqrt($sat->vel->x * $sat->vel->x + $sat->vel->y * $sat->vel->y + $sat->vel->z * $sat->vel->z);
$sat->velo = $sat->vel->w;
Predict_SGPObs::Calculate_Obs($sat->jul_utc, $sat->pos, $sat->vel, $obs_geodetic, $obs_set);
Predict_SGPObs::Calculate_LatLonAlt($sat->jul_utc, $sat->pos, $sat_geodetic);
while ($sat_geodetic->lon < -self::pi) {
$sat_geodetic->lon += self::twopi;
}
while ($sat_geodetic->lon > self::pi) {
$sat_geodetic->lon -= self::twopi;
}
$sat->az = Predict_Math::Degrees($obs_set->az);
$sat->el = Predict_Math::Degrees($obs_set->el);
$sat->range = $obs_set->range;
$sat->range_rate = $obs_set->range_rate;
$sat->ssplat = Predict_Math::Degrees($sat_geodetic->lat);
$sat->ssplon = Predict_Math::Degrees($sat_geodetic->lon);
$sat->alt = $sat_geodetic->alt;
$sat->ma = Predict_Math::Degrees($sat->phase);
$sat->ma *= 256.0 / 360.0;
$sat->phase = Predict_Math::Degrees($sat->phase);
/* same formulas, but the one from predict is nicer */
//sat->footprint = 2.0 * xkmper * acos (xkmper/sat->pos.w);
$sat->footprint = 12756.33 * acos(self::xkmper / (self::xkmper + $sat->alt));
$age = $sat->jul_utc - $sat->jul_epoch;
$sat->orbit = floor(($sat->tle->xno * self::xmnpda / self::twopi + $age * $sat->tle->bstar * self::ae) * $age + $sat->tle->xmo / self::twopi) + $sat->tle->revnum - 1;
}
/**
* Experimental attempt at calculating apparent magnitude. Known intrinsic
* magnitudes are listed inside the function for now.
*
* @param float $time The daynum the satellite is calculated for
* @param Predict_QTH $qth The observer location
*
* @return null on failure, float otherwise
*/
public function calculateApparentMagnitude($time, Predict_QTH $qth)
{
// Recorded intrinsic magnitudes and their respective
// illumination and distance from heavens-above.com
static $intrinsicMagnitudes = array('25544' => array('mag' => -1.3, 'illum' => 0.5, 'distance' => 1000));
// Return null if we don't have a record of the intrinsic mag
if (!isset($intrinsicMagnitudes[$this->tle->catnr])) {
return null;
}
$imag = $intrinsicMagnitudes[$this->tle->catnr];
// Convert the observer's geodetic info to radians and km so
// we can compare vectors
$observerGeo = new Predict_Geodetic();
$observerGeo->lat = Predict_Math::Radians($qth->lat);
$observerGeo->lon = Predict_Math::Radians($qth->lon);
$observerGeo->alt = $qth->alt * 1000;
// Now determine the sun and observer positions
$observerPos = new Predict_Vector();
$observerVel = new Predict_Vector();
$solarVector = new Predict_Vector();
Predict_Solar::Calculate_Solar_Position($time, $solarVector);
Predict_SGPObs::Calculate_User_PosVel($time, $observerGeo, $observerPos, $observerVel);
// Determine the solar phase and and thus the percent illumination
$observerSatPos = new Predict_Vector();
Predict_Math::Vec_Sub($this->pos, $observerPos, $observerSatPos);
$phaseAngle = Predict_Math::Degrees(Predict_Math::Angle($solarVector, $observerSatPos));
$illum = $phaseAngle / 180;
$illuminationChange = $illum / $imag['illum'];
$inverseSquareOfDistanceChange = pow($imag['distance'] / $this->range, 2);
$changeInMagnitude = log($illuminationChange * $inverseSquareOfDistanceChange, self::POGSONS_RATIO);
return $imag['mag'] - $changeInMagnitude;
}
