/**
* Expects a polygon that is "unwrapped", i.e. if the polygon should cross
* the antimeridian, its longitude coordinates are appropriately extended
* to a coordinate system stretching from -360° west to 360° east.
*
* @param Polygon $polygon
* @return ViewBounds
*/
public static function fromPolygon(Polygon $polygon)
{
$points = $polygon->points();
// Initialise extremes with first point's coordinates
$n = $points[0]->y();
$e = $points[0]->x();
$s = $points[0]->y();
$w = $points[0]->x();
// Extend the bounds correspondingly
foreach ($points as $point) {
$n = max($n, $point->y());
$e = max($e, $point->x());
$s = min($s, $point->y());
$w = min($w, $point->x());
}
// Instantiate ViewBounds accordingly, then return
return new ViewBounds(new LatLng($s, $w), new LatLng($n, $e));
}
public static function area(Polygon $polygon)
{
$points = $polygon->points();
$r = 6378;
$lam1 = 0;
$lam2 = 0;
$beta1 = 0;
$beta2 = 0;
$cosB1 = 0;
$cosB2 = 0;
$hav = 0;
$sum = 0;
$lat = [];
$lng = [];
for ($i = 0; $i < count($points); $i++) {
array_push($lat, $points[$i]->y() * pi() / 180);
array_push($lng, $points[$i]->x() * pi() / 180);
}
for ($j = 0; $j < count($lat); $j++) {
$k = $j + 1;
if ($j == 0) {
$lam1 = $lng[$j];
$beta1 = $lat[$j];
$lam2 = $lng[$j + 1];
$beta2 = $lat[$j + 1];
$cosB1 = cos($beta1);
$cosB2 = cos($beta2);
} else {
$k = ($j + 1) % count($lat);
$lam1 = $lam2;
$beta1 = $beta2;
$lam2 = $lng[$k];
$beta2 = $lat[$k];
$cosB1 = $cosB2;
$cosB2 = cos($beta2);
}
if ($lam1 != $lam2) {
$hav = (1.0 - cos($beta2 - $beta1)) / 2.0 + $cosB1 * $cosB2 * ((1.0 - cos($lam2 - $lam1)) / 2.0);
$a = 2 * asin(sqrt($hav));
$b = pi() / 2 - $beta2;
$c = pi() / 2 - $beta1;
$s = 0.5 * ($a + $b + $c);
$t = tan($s / 2) * tan(($s - $a) / 2) * tan(($s - $b) / 2) * tan(($s - $c) / 2);
$excess = abs(4 * atan(sqrt(abs($t))));
if ($lam2 < $lam1) {
$excess = -$excess;
}
$sum += $excess;
}
}
return abs($sum) * $r * $r;
}
