How to Determine if a Point Lies Inside a Polygon Using PHP?

Finding Points Within a Polygon Using PHP

Determining whether a point lies inside a polygon can be a common task in geometric calculations. Here's how to achieve this in PHP:

We begin with a polygon represented as an array of vertices with latitude and longitude coordinates. Additionally, we have a point with similar coordinates that we want to check if it lies within the polygon.

To perform this check, we utilize a function originally written in another language and converted to PHP:

<code class="php">$isInside = is_in_polygon(
    count($vertices_x) - 1,
    $vertices_x,
    $vertices_y,
    $longitude_x,
    $latitude_y
);</code>

The is_in_polygon function implements the following algorithm:

<code class="php">function is_in_polygon($points_polygon, $vertices_x, $vertices_y, $longitude_x, $latitude_y)
{
    $i = $j = $c = 0;
    for ($i = 0, $j = $points_polygon ; $i < $points_polygon; $j = $i++) {
        if ( (($vertices_y[$i]  >  $latitude_y != ($vertices_y[$j] > $latitude_y)) &amp;&amp;
         ($longitude_x < ($vertices_x[$j] - $vertices_x[$i]) * ($latitude_y - $vertices_y[$i]) / ($vertices_y[$j] - $vertices_y[$i]) + $vertices_x[$i]) ) )
           $c = !$c;
    }
    return $c;
}</code>

If the $isInside variable is set to true, the point lies within the polygon; otherwise, it lies outside.

Additional Resources:

For further polygon-related functions, consider using the polygon.php class. Initialize it with your polygon vertices and call the isInside function with your test point to obtain another solution to the problem.

The above is the detailed content of How to Determine if a Point Lies Inside a Polygon Using PHP?. For more information, please follow other related articles on the PHP Chinese website!