/**
* Returns (signed) distance from ‘this’ point to great circle defined by start-point and end-point.
*
* @param LatLon $pathStart - Start point of great circle path.
* @param LatLon $pathEnd - End point of great circle path.
* @param number $radius [radius=6371e3] - (Mean) radius of earth (defaults to radius in metres).
* @returns number Distance to great circle (-ve if to left, +ve if to right of path).
*
* @example
* $pCurrent = new LatLon(53.2611, -0.7972);
* $p1 = new LatLon(53.3206, -1.7297); $p2 = new LatLon(53.1887, 0.1334);
* $d = $pCurrent->crossTrackDistanceTo($p1, $p2); // round($d, 1): -307.5
*/
public function crossTrackDistanceTo(LatLon $pathStart, LatLon $pathEnd, $radius = null)
{
$radius = $radius === null ? static::RADIUS : (double) $radius;
$δ13 = $pathStart->distanceTo($this, $radius) / $radius;
$θ13 = deg2rad($pathStart->bearingTo($this));
$θ12 = deg2rad($pathStart->bearingTo($pathEnd));
$dxt = asin(sin($δ13) * sin($θ13 - $θ12)) * $radius;
return $dxt;
}
