Hello,

Sharing the alternative that I used to solve the problem.

Basically is the sum of the products of the vertices

With a closed polygon, my script looked something like this:

$max_i = $total_rows - 1;

$i = 0;

$area = 0;

while ($i < $max_i){

    $area = $area + (($x[$i] * $y[$i+1]) - ($y[$i] * $x[$i+1]));

    $i ++;

}

if ($area < 0){ $area = $area * -1; }

$area = $area / 2;

Source:
https://www.mathopenref.com/coordpolygonarea.html

There are some solutions available here as well:

How do I calculate the area of a 2d polygon?