How Can I Calculate Geographic Distance Using PHP\'s Haversine and Vincenty Formulas?

Determining Geographic Distance with PHP Coordinates

Calculating the distance between two geographical coordinates involves the Haversine or Vincenty formulas.

Haversine Formula

The Haversine formula, implemented in the following PHP code:

class CoordDistance {
    // Latitude and longitude of points A and B
    public $lat_a, $lon_a, $lat_b, $lon_b;
    public $earth_radius = 6372.795477598;
    public $distance;

    public function DistAB() {
        $latDelta = $this->lat_b - $this->lat_a;
        $lonDelta = $this->lon_b - $this->lon_a;
        $alpha = $latDelta / 2;
        $beta = $lonDelta / 2;
        $a = sin(deg2rad($alpha)) * sin(deg2rad($alpha)) +
              cos(deg2rad($this->lat_a)) * cos(deg2rad($this->lat_b)) *
              sin(deg2rad($beta)) * sin(deg2rad($beta));
        $c = asin(min(1, sqrt($a)));
        $distance = 2 * $this->earth_radius * $c;
        $this->distance = $distance;
    }
}

Vincenty Formula

For antipodal points, the Vincenty formula is more accurate:

class CoordDistance {
    // Latitude and longitude of points A and B
    public $lat_a, $lon_a, $lat_b, $lon_b;
    public $earth_radius = 6371000;
    public $distance;

    public function DistAB() {
        // Convert to radians
        $latFrom = deg2rad($this->lat_a);
        $lonFrom = deg2rad($this->lon_a);
        $latTo = deg2rad($this->lat_b);
        $lonTo = deg2rad($this->lon_b);

        $lonDelta = $lonTo - $lonFrom;
        $a = pow(cos($latTo) * sin($lonDelta), 2) +
              pow(cos($latFrom) * sin($latTo) -
                sin($latFrom) * cos($latTo) * cos($lonDelta), 2);
        $b = sin($latFrom) * sin($latTo) +
              cos($latFrom) * cos($latTo) * cos($lonDelta);

        $angle = atan2(sqrt($a), $b);
        $distance = $angle * $this->earth_radius;
        $this->distance = $distance;
    }
}

Both formulas return the distance in the same unit of measurement as the provided earth's radius.

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