Polygon points inside or outside check in php

by Prabakaran 2012-07-30 15:51:37

<?php
class pointLocation {
var $pointOnVertex = true; // Check if the point sits exactly on one of the vertices

function pointLocation() {
}


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";
}
}



function pointOnVertex($point, $vertices) {
foreach($vertices as $vertex) {
if ($point == $vertex) {
return true;
}
}

}


function pointStringToCoordinates($pointString) {
$coordinates = explode(" ", $pointString);
return array("x" => $coordinates[0], "y" => $coordinates[1]);
}


}

/*** Example ***/
$pointLocation = new pointLocation();
$points = array("30 19", "0 0", "10 0", "30 20", "11 0", "0 11", "0 10", "30 22", "20 20");
$polygon = array("10 0", "20 0", "30 10", "30 20", "20 30", "10 30", "0 20", "0 10", "10 0");
// The last point's coordinates must be the same as the first one's, to "close the loop"
foreach($points as $key => $point) {
echo "$key ($point) is " . $pointLocation->pointInPolygon($point, $polygon) . "<br>";
}
?>
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