Create geofence from point and distance

cockney.geojson

{
   "type":"FeatureCollection",
   "features":[
      {
         "type":"Feature",
         "properties":{
            
         },
         "geometry":{
            "coordinates":[
               [
                  [
                     -0.09365209962467438,
                     51.558654593845496
                  ],
                  [
                     -0.10617136382247229,
                     51.557971183635146
                  ],
                  [
                     -0.11830913972151091,
                     51.55594177797345
                  ],
                  [
                     -0.12969566311540492,
                     51.55262821175705
                  ],
                  [
                     -0.13998424561019743,
                     51.5481314301052
                  ],
                  [
                     -0.14886189489846346,
                     51.542588389225116
                  ],
                  [
                     -0.15605887044720881,
                     51.53616785590004
                  ],
                  [
                     -0.1613568787964777,
                     51.52906523798585
                  ],
                  [
                     -0.16459565962665132,
                     51.521496608030176
                  ],
                  [
                     -0.16567776823852612,
                     51.51369210631598
                  ],
                  [
                     -0.1645714197450512,
                     51.505888927589325
                  ],
                  [
                     -0.16131132271079096,
                     51.49832410702523
                  ],
                  [
                     -0.15599749287830883,
                     51.49122732543967
                  ],
                  [
                     -0.14879209887336683,
                     51.48481395143504
                  ],
                  [
                     -0.1399144495543639,
                     51.47927852934888
                  ],
                  [
                     -0.1296342854684414,
                     51.47478890702547
                  ],
                  [
                     -0.11826358354717573,
                     51.47148117714999
                  ],
                  [
                     -0.10614712388296067,
                     51.469455580890696
                  ],
                  [
                     -0.09365209962467438,
                     51.46877349367216
                  ],
                  [
                     -0.0811570753663881,
                     51.469455580890696
                  ],
                  [
                     -0.06904061570227482,
                     51.47148117714999
                  ],
                  [
                     -0.057669913781009136,
                     51.47478890702547
                  ],
                  [
                     -0.047389749695086615,
                     51.47927852934888
                  ],
                  [
                     -0.0385121003760837,
                     51.48481395143504
                  ],
                  [
                     -0.03130670637114172,
                     51.49122732543967
                  ],
                  [
                     -0.025992876538659594,
                     51.49832410702523
                  ],
                  [
                     -0.022732779504399312,
                     51.505888927589325
                  ],
                  [
                     -0.021626431010924405,
                     51.51369210631598
                  ],
                  [
                     -0.022708539622799232,
                     51.521496608030176
                  ],
                  [
                     -0.025947320452972822,
                     51.52906523798586
                  ],
                  [
                     -0.03124532880224173,
                     51.53616785590004
                  ],
                  [
                     -0.03844230435098709,
                     51.542588389225116
                  ],
                  [
                     -0.04731995363915135,
                     51.5481314301052
                  ],
                  [
                     -0.05760853613404561,
                     51.55262821175705
                  ],
                  [
                     -0.06899505952783784,
                     51.55594177797345
                  ],
                  [
                     -0.08113283542697826,
                     51.557971183635146
                  ],
                  [
                     -0.09365209962467438,
                     51.558654593845496
                  ]
               ]
            ],
            "type":"Polygon"
         }
      }
   ]
}

geofence.php

<?php

use Location\Bearing\BearingEllipsoidal;
use Location\Coordinate;
use Location\Formatter\Polygon\GeoJSON;
use Location\Polygon;

// Let's start at the church of St Mary-le-Bow in London...
$maryLeBow = new Coordinate(51.51371421689447, -0.09365209962470467);

// One definition of a London cockney was that they were born in
// earshot of that church's bells. Let's say that the bells ring
// out for 3 miles (around 5000 meters)...
$distance = 5000;

// We can create a polygon to hold our definition of cockney, a geofence
// of 5000 meters around St Mary-le-Bow.
$cockney = new Polygon();

// Create a bearing calculator to use
$calculator = new BearingEllipsoidal();

// Iterate from a starting bearing of 360 (due north) and then decrease
// our bearing by 10 degrees each time. We decrease from 360 rather than
// increase from 0 so that we're following the "right-hand rule" where
// coordinates for outer polygons are in counter-clockwise order.
for ($bearing = 360; $bearing >= 0; $bearing -= 10) {
    // Use the calculator to get a new point 5000 meters from Mary-le-Bow
    // in our bearing direction and add it to the polygon. The result is
    // a 36-point polygon forming a rough circle around the church.
    $cockney->addPoint($calculator->calculateDestination($maryLeBow, $bearing % 360, $distance));
}

// Create a new GeoJSON formatter to output our geofence polygon
echo (new GeoJSON())->format($cockney);