Check if coordinates is within a specific distance from other coordinates

coordinates, distance, match, math, php

Solution

You can do this using Great Circle algorithms. http://en.wikipedia.org/wiki/Great-circle_distance

Here's how to find distance.

EDIT

Here is the full code for you to do that!

<?php
$persons = Array();

$persons[] = Array('52.00951','4.36052');//Delft is more than 2 km from den haag
$persons[] = Array('52.03194','4.31769');//Rijswijk is less than 2 km from den haag
$persons[] = Array('52.07097','4.29945');//A place near den Haag almost 2 streets from center and my favourite coffee shop
$persons[] = Array('52.37022','4.89517');//Amsterdamn is about 60 km *DRIVING* from the hagues according to Gmaps

$target = Array('52.07050', '4.30070');//Den Haag
$i = 0;
foreach($persons as $person){
    $i++;
    $distance = calculate_distance($person, $target);
    if($distance <= 2 ){ 
        echo "Person $i is within 2km with a distance to taget of $distance</br>";
    }else{
        echo "Person $i is <b>not</b> within 2km with a distance to taget of $distance</br>";
    }

}

function calculate_distance($person, $target){

    $lat1 = $person[0];
    $lng1 = $person[1];
    $lat2 = $target[0];
    $lng2 = $target[1];
    $pi = 3.14159;
    $rad = doubleval($pi/180.0);

    $lon1 = doubleval($lng1)*$rad;
    $lat1 = doubleval($lat1)*$rad; 
    $lon2 = doubleval($lng2)*$rad; 
    $lat2 = doubleval($lat2)*$rad; 
    $theta = $lng2 - $lng1; 

    $dist = acos(sin($lat1) * sin($lat2) + cos($lat1) * cos($lat2) * cos($theta)); 

    if ($dist < 0) 
        $dist += $pi;


    $miles = doubleval($dist * 69.1); 
    $inches = doubleval($miles * 63360); 
    $km  =  doubleval($dist * 115.1666667);

    $dist = sprintf( "%.2f",$dist); 
    $miles = sprintf( "%.2f",$miles); 
    $inches = sprintf( "%.2f",$inches); 
    $km = sprintf( "%.2f",$km);
    //Here you can return whatever you please
    return $km;
}

?>

And of course the results:

Person 1 is not within 2km with a distance to taget of 4.24
Person 2 is within 2km with a distance to taget of 1.21
Person 3 is within 2km with a distance to taget of 0.09
Person 4 is not within 2km with a distance to taget of 41.56

Problem

Original source