Check if geolocation is within boundaries

Question

I'm trying to generate some geolocations within the borders of an area right now I'm trying to generate geo locations within these boundaries

$bounds = array(
    array(55.4024447, 13.1656691),
    array(56.1575776, 15.8350261),
    array(68.0410163, 17.4600359),
    array(58.9380148, 11.3501468),
    array(67.6820048, 16.1964251)
);

and right now my checking for this is as follows

if (
    ($bounds[0][0] < $lat && $bounds[0][1] < $lng) &&
    ($bounds[1][0] < $lat && $bounds[1][1] > $lng) &&
    ($bounds[2][0] > $lat && $bounds[2][1] > $lng) &&
    ($bounds[3][0] > $lat && $bounds[3][1] < $lng) &&
    ($bounds[4][0] > $lat && $bounds[4][1] > $lng)
) {

however this only gets locations within a square in the middle not in the entire area do you have any idea of how to check within the full area instead?

Answer 1

The following PHP code uses point in polygon algorithm described at the wikipedia.

In Fig 1 point is in polygon and the line drawn from this crosses the perimeter of the polygon an odd number of times(3). In Fig 2 the line crosses the perimeter an even number of times(4) and the point is outside.

<?php

function pointInPolygon($polySides,$polyX,$polyY,$x,$y) {
  $j = $polySides-1 ;
  $oddNodes = 0;
  for ($i=0; $i<$polySides; $i++) {
    if ($polyY[$i]<$y && $polyY[$j]>=$y  ||  $polyY[$j]<$y && $polyY[$i]>=$y) {
        if ($polyX[$i]+($y-$polyY[$i])/($polyY[$j]-$polyY[$i])*($polyX[$j]-$polyX[$i])<$x)  {
            $oddNodes=!$oddNodes; 
        }
    }
   $j=$i; }

  return $oddNodes;
}
$polySides = 3;
$x =60;
$y =15;
$polyX = array(55.4024447,56.1575776,68.0410163,67.6820048,58.9380148,55.4024447);// First point repeated to close polygon coordinates 
$polyY = array(13.1656691,15.8350261,17.4600359,16.1964251,11.3501468,13.1656691); 
if (pointInPolygon($polySides,$polyX,$polyY,$x,$y)){
    echo "Point In Polygon";
    }else{
    echo "Point Not In Polygon";
    }
?>