Generate random coordinates around a location

Question

I\'d like to have a function that accepts a geo location (Latitude, Longitude) and generates random sets of coordinates around it but also takes these parameters as a part of th

Answer 1

Generate random coordinates around a location

function generateRandomPoint($centre, $radius) {
    $radius_earth = 3959; //miles

    //Pick random distance within $distance;
    $distance = lcg_value()*$radius;

    //Convert degrees to radians.
    $centre_rads = array_map( 'deg2rad', $centre );

    //First suppose our point is the north pole.
    //Find a random point $distance miles away
    $lat_rads = (pi()/2) -  $distance/$radius_earth;
    $lng_rads = lcg_value()*2*pi();


    //($lat_rads,$lng_rads) is a point on the circle which is
    //$distance miles from the north pole. Convert to Cartesian
    $x1 = cos( $lat_rads ) * sin( $lng_rads );
    $y1 = cos( $lat_rads ) * cos( $lng_rads );
    $z1 = sin( $lat_rads );


    //Rotate that sphere so that the north pole is now at $centre.

    //Rotate in x axis by $rot = (pi()/2) - $centre_rads[0];
    $rot = (pi()/2) - $centre_rads[0];
    $x2 = $x1;
    $y2 = $y1 * cos( $rot ) + $z1 * sin( $rot );
    $z2 = -$y1 * sin( $rot ) + $z1 * cos( $rot );

    //Rotate in z axis by $rot = $centre_rads[1]
    $rot = $centre_rads[1];
    $x3 = $x2 * cos( $rot ) + $y2 * sin( $rot );
    $y3 = -$x2 * sin( $rot ) + $y2 * cos( $rot );
    $z3 = $z2;


    //Finally convert this point to polar co-ords
    $lng_rads = atan2( $x3, $y3 );
    $lat_rads = asin( $z3 );

    return array_map( 'rad2deg', array( $lat_rads, $lng_rads ) );
}

Usage

generateRandomPoint(array(3.1528, 101.7038), 4);