PHP Library: Calculate a bounding box for a given lat/lng location

Question

I'm looking for a PHP Library / PHP Script that allows me to calculate an accurate bounding box for a given center point (lat/lon).

Using an ellipsoid formula (f.ex. WGS84) would be great. I know, there have to be a library but I'm not able to find one.

Answer 1

Function is wrong after the // bearings bit, it should be as follows:

function getBoundingBox($lat_degrees,$lon_degrees,$distance_in_miles) {

    $radius = 3963.1; // of earth in miles

    // bearings - FIX   
    $due_north = deg2rad(0);
    $due_south = deg2rad(180);
    $due_east = deg2rad(90);
    $due_west = deg2rad(270);

    // convert latitude and longitude into radians 
    $lat_r = deg2rad($lat_degrees);
    $lon_r = deg2rad($lon_degrees);

    // find the northmost, southmost, eastmost and westmost corners $distance_in_miles away
    // original formula from
    // http://www.movable-type.co.uk/scripts/latlong.html

    $northmost  = asin(sin($lat_r) * cos($distance_in_miles/$radius) + cos($lat_r) * sin ($distance_in_miles/$radius) * cos($due_north));
    $southmost  = asin(sin($lat_r) * cos($distance_in_miles/$radius) + cos($lat_r) * sin ($distance_in_miles/$radius) * cos($due_south));

    $eastmost = $lon_r + atan2(sin($due_east)*sin($distance_in_miles/$radius)*cos($lat_r),cos($distance_in_miles/$radius)-sin($lat_r)*sin($lat_r));
    $westmost = $lon_r + atan2(sin($due_west)*sin($distance_in_miles/$radius)*cos($lat_r),cos($distance_in_miles/$radius)-sin($lat_r)*sin($lat_r));


    $northmost = rad2deg($northmost);
    $southmost = rad2deg($southmost);
    $eastmost = rad2deg($eastmost);
    $westmost = rad2deg($westmost);

    // sort the lat and long so that we can use them for a between query        
    if ($northmost > $southmost) { 
        $lat1 = $southmost;
        $lat2 = $northmost;

    } else {
        $lat1 = $northmost;
        $lat2 = $southmost;
    }


    if ($eastmost > $westmost) { 
        $lon1 = $westmost;
        $lon2 = $eastmost;

    } else {
        $lon1 = $eastmost;
        $lon2 = $westmost;
    }

    return array($lat1,$lat2,$lon1,$lon2);
}

I got this function thanks to: http://xoxco.com/clickable/php-getboundingbox

Answer 2

This is a relative easy problem to solve if you assume the bounding box runs east-west in one direction and north-south in the other. You can do latitude and longitude independently.

For latitude, sort the points west to east. At that point you have to treat the list as a circular buffer. You need to test each point and find the one with the most distant next point. So assume ten points a₀ to a₉, if a₄ and a₅ are most distant the latitude bounding box is from a₅ round to a₄. Call them a_w and a_e

For longitude, you just need to find the northenmost and southernmost points, call them a_n and a_s.

The longitudes of a_w and a_e and latitudes of a_n and a_s define the bounding box.