Find Point 2 mile away from polygon PHP

Question

I have the polygon data, in the form of an array of latitudes and longitudes in mysql database, ex:

an array of latitudes and longitudes in mysql database.

[["x":23.628134,  "y":27.458334],
["x":23.629867,   "y":27.449021],
["x":23.62324,    "y":27.445416],
["x":23.622424,   "y":27.457819],
["x":23.622424,   "y":27.457819]]

And i have a point (Vertex) with coordinates of latitude and longitude, ex:

$location = new vertex($_GET["longitude"], $_GET["latitude"]);

Now i want to find whether this vertex (point) is 2 miles away from each corner of the polygon or not. How can i do this in php?

score 1 · Accepted Answer · answered Aug 08 '14 at 07:49

If you consider that your points are near compare to the size of the earth, you could compute distance from a coordinate to another using this formula :

It's a csharp function but easy to port to php

    double getGroundDistance(double latA, double lonA, double latB, double lonB)
    {
        double a = Math.PI / 180;
        double lat1 = latA * a;
        double lat2 = latB * a;
        double lon1 = lonA * a;
        double lon2 = lonB * a;
        double t1 = Math.Sin(lat1) * Math.Sin(lat2);
        double t2 = Math.Cos(lat1) * Math.Cos(lat2);
        double t3 = Math.Cos(lon1 - lon2);
        double t4 = t2 * t3;
        double t5 = t1 + t4;
        double radDist = Math.Atan(-t5 / Math.Sqrt(-t5 * t5 + 1)) + 2 * Math.Atan(1);
        return (radDist * 3437.74677 * 1.1508) * 1.6093470878864446 * 1000;
    }

So you just need to check your distance from each point.

Hope it help

score 1 · Answer 2 · answered Aug 08 '14 at 07:59

Here i Port that code in PHP

 Private function Distance($lat1, $lon1, $lat2, $lon2) {
    $pi80 = M_PI / 180;
    $lat1 *= $pi80;
    $lon1 *= $pi80;
    $lat2 *= $pi80;
    $lon2 *= $pi80;
    $r = 6372.797; // mean radius of Earth in km
    $dlat = $lat2 - $lat1;
    $dlon = $lon2 - $lon1;
    $a = sin($dlat / 2) * sin($dlat / 2) + cos($lat1) * cos($lat2) * sin($dlon / 2) * sin($dlon / 2);
    $c = 2 * atan2(sqrt($a), sqrt(1 - $a));
    $km = $r * $c;

    return $km;
}

Find Point 2 mile away from polygon PHP

2 Answers2