How can I determine if a point is inside a polygon in PHP?

Point-in-Polygon Algorithm in PHP

Problem:

Given an array of latitude and longitude coordinates defining a polygon and a point with similar coordinates, determine if the point lies within the polygon's boundaries.

Implementation:

PHP provides a function for solving this problem, using a classic point-in-polygon algorithm. The function is:

<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>

Usage:

To use the function, provide it with the following parameters:

• $points_polygon: The number of vertices in the polygon (zero-based array).
• $vertices_x: An array of x-coordinates for the polygon's vertices.
• $vertices_y: An array of y-coordinates for the polygon's vertices.
• $longitude_x: The x-coordinate of the point to test.
• $latitude_y: The y-coordinate of the point to test.

The function returns true if the point lies within the polygon and false otherwise.

Additional Note:

PHP also provides a polygon.php class that contains several polygon-related functions, including isInside, which can be used to determine if a point is within a polygon.

The above is the detailed content of How can I determine if a point is inside a polygon in PHP?. For more information, please follow other related articles on the PHP Chinese website!