/**
* Creates a new Cartesian vector instance
*
* @param Frame $frame Reference frame
* @param Epoch|AstroDate $epoch Observation epoch
* @param Distance $x x position
* @param Distance $y y position
* @param Distance $z z position
* @param Velocity $vx x velocity
* @param Velocity $vy y velocity
* @param Velocity $vz z velocity
*/
public function __construct(Frame $frame, $epoch, Distance $x, Distance $y, Distance $z, Velocity $vx = null, Velocity $vy = null, Velocity $vz = null)
{
// Set reference frame and observation epoch
$this->frame = $frame;
$this->epoch = $epoch instanceof Epoch ? $epoch : $epoch->toEpoch();
// Set position components
$this->x = $x;
$this->y = $y;
$this->z = $z;
// Set velocity components
$this->vx = $vx;
$this->vy = $vy;
$this->vz = $vz;
// Set default rounding and units
$this->decimalPlaces = 13;
}
/**
* Converts this instance to an AstroDate instance
* @return AstroDate
*/
public function toDate()
{
if ($this->dt) {
return $this->dt;
} else {
return AstroDate::jd($this->jd, TimeScale::TT());
}
}
/**
* Finds the accurate time of a solstice or equinox using the complete VSOP87
* theory
*
* @param int $year The year to find a solstice or equinox for
* @param array $terms An array of the mean terms for the desired equinox or
* solstice
* @param int $month The month of the equinox or solstice to find
*
* @return float The JD of the solstice or equinox in TD
*/
private static function accurate($year, array $terms, $month)
{
$Y = $year < 1000 ? (int) $year / 1000 : ((int) $year - 2000) / 1000;
$q = intval($month / 3) - 1;
$jde0 = static::Horner($Y, $terms);
for ($i = 0; $i < 100; $i++) {
// TODO:: use vsop 87, but use IAU apparent stuff?
$λ = Solar::ApparentEclVSOP87(AstroDate::fromJD($jde0))->λ->rad;
$Δ = 58 * sin(deg2rad($q * 90) - $λ);
$jde0 += $Δ;
if (abs($Δ) < 5.0E-7) {
break;
}
}
return $jde0;
}
/**
* @covers Marando\AstroDate\Epoch::toDate
*/
public function testToDate()
{
$dt = Epoch::J2000()->toDate();
$expected = AstroDate::jd(2451545.0, TimeScale::TT());
$this->assertEquals($expected->toJD(), $dt->toJD());
}