Polygon area calculation using Latitude and Longitude generated from Cartesian space and a world file

Question

Given a series of GPS coordinate pairs, I need to calculate the area of a polygon (n-gon). This is relatively small (not larger than 50,000 sqft). The geocodes are created

Answer 1

Adapted RiskyPathak's snippet to PHP

function CalculatePolygonArea($coordinates) {
    $area = 0;
    $coordinatesCount = sizeof($coordinates);
    if ($coordinatesCount > 2) {
      for ($i = 0; $i < $coordinatesCount - 1; $i++) {
        $p1 = $coordinates[$i];
        $p2 = $coordinates[$i + 1];
        $p1Longitude = $p1[0];
        $p2Longitude = $p2[0];
        $p1Latitude = $p1[1];
        $p2Latitude = $p2[1];
        $area += ConvertToRadian($p2Longitude - $p1Longitude) * (2 + sin(ConvertToRadian($p1Latitude)) + sin(ConvertToRadian($p2Latitude)));
      }
    $area = $area * 6378137 * 6378137 / 2;
    }
    return abs(round(($area));
}

function ConvertToRadian($input) {
    $output = $input * pi() / 180;
    return $output;
}