A directus.io custom endpoint to get distance based on coordinates. Put this file in `public/extensions/custom/endpoints/` and access it via `{{api_url}}/custom/locations?lat=LATITUDE_TO_CHECK_AGAINST&lng=LONGITUDE_TO_CHECK_AGAINST`

locations.php

<?php

use Directus\Application\Http\Request;
use Directus\Application\Http\Response;
use Directus\Services\ItemsService;
use Zend\Db\Adapter\Adapter;

return [
    // The endpoint path:
    // '' means it is located at: `/custom/<endpoint-id>`
    // '/` means it is located at: `/custom/<endpoint-id>/`
    // 'test' and `/test` means it is located at: `/custom/<endpoint-id>/test
    // if the handler is a Closure or Anonymous function, it's binded to the app container. Which means $this = to the app container.
    '' => [
        'method' => 'GET',
        'handler' => function (Request $request, Response $response) {
            $container = \Directus\Application\Application::getInstance()->getContainer();
            $dbConnection = $container->get('database');
            $acl = $container->get('acl');
            $itemsService = new ItemsService($this);
            
            $params = $request->getQueryParams();
            
            if ($acl->canRead('locations')) {
                $lat = "json_extract(coordinates, '$.lat')";
                $lng = "json_extract(coordinates, '$.lng')";
                
                // 6731000 is the earth radius in meters
                $sql = "SELECT id,"
                    . " 6731000 * 2 * ASIN(SQRT(POWER(SIN((" . $params["lat"] . " - abs(" . $lat . ")) * pi()/180 / 2), 2)"
                    . " + COS(" . $params["lng"] . " * pi()/180 ) * COS(abs(" . $lat . ") * pi()/180)"
                    . " * POWER(SIN((" . $params["lng"] . " - " . $lng . ") * pi()/180 / 2), 2) )) as distance"
                    . " FROM `locations`";
                
                // this is some custom filter applicable in my case
                // if (isset($params["filter"]["city"])) {
                //   $sql = $sql . " WHERE city = " . $params["filter"]["city"]["eq"];
                // }
                
                if (isset($params["distance"])) {
                    $sql = $sql . " HAVING distance < " . $params["distance"];
                }
                
                // print_r($sql);
    
                $result = $dbConnection->query($sql, Adapter::QUERY_MODE_EXECUTE);
                $result = $result->toArray();
            }
            
            $locations = $itemsService->findAll('locations', $params);
            
            $final = array_replace_recursive($locations["data"], $result);
    
            return $response->withJson([
                'data' => $final,
            ]);
        }
    ],
];