php: finding latitude and longitude boundaries based on a central lat/lng and distance

I was working with the solution to a very similar question and upon implementation I discovered that it was producing a tall rectangle with the returned coordinates instead of a square (please see Matthias' answer to the other question).

I only needed an array to be returned as this is to work with WordPress which has it's own preferred query method.

Here's my implementation:

function bar_get_nearby( $lat, $lng, $limit = 50, $distance = 50, $unit = 'mi' ) {
    
    // radius of earth; @note: the earth is not perfectly spherical, but this is considered the 'mean radius'
    if( $unit == 'km' ) { $radius = 6371.009; }
    elseif ( $unit == 'mi' ) { $radius = 3958.761; }

    // latitude boundaries
    $maxLat = ( float ) $lat + rad2deg( $distance / $radius );
    $minLat = ( float ) $lat - rad2deg( $distance / $radius );

    // longitude boundaries (longitude gets smaller when latitude increases)
    $maxLng = ( float ) $lng + rad2deg( $distance / $radius / cos( deg2rad( ( float ) $lat ) ) );
    $minLng = ( float ) $lng - rad2deg( $distance / $radius / cos( deg2rad( ( float ) $lat ) ) );

    $max_min_values = array(
        'max_latitude' => $maxLat,
        'min_latitude' => $minLat,
        'max_longitude' => $maxLng,
        'min_longitude' => $minLng
    );
    
    return $max_min_values;
    
}

If I give I geocode (via Google Maps API) my desired postcode of G2 1QX and a distance of 5 miles I get a lat/lng of -4.2556347/55.8620472 with the function returning this array:

Array
(
    [max_latitude] => -4.18326890233
    [min_latitude] => -4.32800049767
    [max_longitude] => 55.9346130696
    [min_longitude] => 55.7894813304
)

Any ideas? Many thanks in advance.

Cheers, RS

php latitude-longitude

Edit Report

I once wrote this function to calculate the distance between 2 points in kilometers (km) instead of miles. I wrote a quick modification for the mile answer

/**
 * The Haversine function can be used to calculate the distance between 2 points on a map
 *
 * @param  float $lat1 The longtitude value of the first point
 * @param  float $lon1 The lattitude of the frist point
 * @param  float $lat2 The longtitude value of the second point
 * @param  float $lon2 The lattitude of the second point
 * @return float       The distance between the points in mile
 *
 * @access public
 **/
public function harversineDistance($lat1, $lon1, $lat2, $lon2)
{
    $latd = deg2rad($lat2 - $lat1);
    $lond = deg2rad($lon2 - $lon1);
    $a = sin($latd / 2) * sin($latd / 2) +
        cos(deg2rad($lat1)) * cos(deg2rad($lat2)) *
        sin($lond / 2) * sin($lond / 2);
    $c = 2 * atan2(sqrt($a), sqrt(1 - $a));

    // Original return for the km answer
    //return 6371.0 * $c;

    // Return for the mile answer on 2 digits percision
    return round(((6371.0 * $c) * 0.621371192), 2);
}

answered 2012-09-14T12:54:36.820

php: finding latitude and longitude boundaries based on a central lat/lng and distance

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