<?php
/**
* An example for looking up the current solar position in the sky from a given
* location (elevation/azimuth)
*/
require_once 'Predict/Solar.php';
require_once 'Predict/QTH.php';
// Use current time in the form of a daynum
$time = time();
$daynum = Predict_Time::unix2daynum($time);
// Set up the observer position on the ground
$qth = new Predict_QTH();
$qth->lat = 37.786759;
$qth->lon = -122.405162;
$qth->alt = 10;
// Altitude above sea level in meters
$sunInfo = Predict_Solar::FindSun($qth, $daynum);
$output = array('elevation' => $sunInfo->el, 'azimuth' => $sunInfo->az, 'timestamp' => $time);
// output results
echo json_encode($output);
/**
* Calculate satellite visibility.
*
* @param Predict_Sat $sat The satellite structure.
* @param Predict_QTH $qth The QTH
* @param float $jul_utc The time at which the visibility should be calculated.
*
* @return int The visiblity constant, 0, 1, 2, or 3 (see above)
*/
public function get_sat_vis(Predict_Sat $sat, Predict_QTH $qth, $jul_utc)
{
/* gboolean sat_sun_status;
gdouble sun_el;
gdouble threshold;
gdouble eclipse_depth;
sat_vis_t vis = SAT_VIS_NONE; */
$eclipse_depth = 0.0;
$zero_vector = new Predict_Vector();
$obs_geodetic = new Predict_Geodetic();
/* Solar ECI position vector */
$solar_vector = new Predict_Vector();
/* Solar observed az and el vector */
$solar_set = new Predict_ObsSet();
/* FIXME: could be passed as parameter */
$obs_geodetic->lon = $qth->lon * self::de2ra;
$obs_geodetic->lat = $qth->lat * self::de2ra;
$obs_geodetic->alt = $qth->alt / 1000.0;
$obs_geodetic->theta = 0;
Predict_Solar::Calculate_Solar_Position($jul_utc, $solar_vector);
Predict_SGPObs::Calculate_Obs($jul_utc, $solar_vector, $zero_vector, $obs_geodetic, $solar_set);
if (Predict_Solar::Sat_Eclipsed($sat->pos, $solar_vector, $eclipse_depth)) {
/* satellite is eclipsed */
$sat_sun_status = false;
} else {
/* satellite in sunlight => may be visible */
$sat_sun_status = true;
}
if ($sat_sun_status) {
$sun_el = Predict_Math::Degrees($solar_set->el);
if ($sun_el <= $this->threshold && $sat->el >= 0.0) {
$vis = self::SAT_VIS_VISIBLE;
} else {
$vis = self::SAT_VIS_DAYLIGHT;
}
} else {
$vis = self::SAT_VIS_ECLIPSED;
}
return $vis;
}
<?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));
/**
* 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;
}
