Point in Polygon Algorythm for CodeIgniter

[eluser]Gizmo84[/eluser]
Hi all,

This is my first contributing post in CI forums so be gentle. I was creating a map application that detected GPS locations withing a certain area via a polygon and after some google searching I found the Point-in-Polygon Algorithm.

I originally got the code from http://www.assemblysys.com/dataServices/php.php where I have only made necessary changes to port the class as a library in CI.

Here is the ported Library

Code:

<?php if(!defined("BASEPATH")) exit("No direct script access allowed");
  
  /**
  * pointLocation for CodeIgniter
  *
  * @package    CodeIgniter
  * @subpackage libraries
  * @category   library
  * @version    1.0
  * @author     Steven Richardson <[email protected]>
  * @link       http://ellislab.com/forums/viewthread/160896/
  */
  class pointLocation
  {

    public function __construct(){
    }
  
    var $pointOnVertex = true; // Check if the point sits exactly on one of the vertices
  
    
    public function pointInPolygon($point, $polygon, $pointOnVertex = true) {
        
        $this->pointOnVertex = $pointOnVertex;
        
        // Transform string coordinates into arrays with x and y values
        $point = $this->pointStringToCoordinates($point);
        $vertices = array();
        foreach ($polygon as $vertex) {
            $vertices[] = $this->pointStringToCoordinates($vertex);
        }
        
        // Check if the point sits exactly on a vertex
        if ($this->pointOnVertex == true and $this->pointOnVertex($point, $vertices) == true) {
            return "vertex";
        }
        
        // Check if the point is inside the polygon or on the boundary
        $intersections = 0;
        $vertices_count = count($vertices);
    
        for ($i=1; $i < $vertices_count; $i++) {
            $vertex1 = $vertices[$i-1];
            $vertex2 = $vertices[$i];
            if ($vertex1['y'] == $vertex2['y'] and $vertex1['y'] == $point['y'] and $point['x'] > min($vertex1['x'], $vertex2['x']) and $point['x'] < max($vertex1['x'], $vertex2['x'])) { // Check if point is on an horizontal polygon boundary
                return "boundary";
            }
            if ($point['y'] > min($vertex1['y'], $vertex2['y']) and $point['y'] <= max($vertex1['y'], $vertex2['y']) and $point['x'] <= max($vertex1['x'], $vertex2['x']) and $vertex1['y'] != $vertex2['y']) {
                $xinters = ($point['y'] - $vertex1['y']) * ($vertex2['x'] - $vertex1['x']) / ($vertex2['y'] - $vertex1['y']) + $vertex1['x'];
                if ($xinters == $point['x']) { // Check if point is on the polygon boundary (other than horizontal)
                    return "boundary";
                }
                if ($vertex1['x'] == $vertex2['x'] || $point['x'] <= $xinters) {
                    $intersections++;
                }
            }
        }
        // If the number of edges we passed through is even, then it's in the polygon.
        if ($intersections % 2 != 0) {
            return "inside";
        } else {
            return "outside";
        }
    }

    protected function pointOnVertex($point, $vertices) {
        foreach($vertices as $vertex) {
            if ($point == $vertex) {
                return true;
            }
        }
    
    }
    
    protected function pointStringToCoordinates($pointString) {
        $coordinates = explode(" ", $pointString);
        return array("x" => $coordinates[0], "y" => $coordinates[1]);
    }
    
    
}

To call this library make sure you load the library in your controller then call the functions like so:

Code:

$this->load->library("PointLocation");
        
$points = array("30 19", "0 0", "10 0", "30 20", "11 0", "0 11", "0 10", "30 22", "20 20");
$polygon = array("10 0", "20 0", "30 10", "30 20", "20 30", "10 30", "0 20", "0 10", "10 0");
foreach($points as $key => $point) {
   echo "$key ($point) is " . $this->pointlocation->pointInPolygon($point, $polygon) . "<br>";
}

And thats all folks, not much to it but thought I should share as it maybe just what you are looking for.