FacetWP - index GeoMyWP coordinates

functions.php

<?php
/**
 * Setup instructions:
 *
 * 1. Add the following code to your (child) theme's functions.php
 * 2. Create a new facet named "location"
 * 3. Set the facet type to "Proximity"
 * 4. Set the facet's Data source to "Post Type" (as a placeholder)
 * 5. Save and re-index
 */

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'location' == $params['facet_name'] ) {
        global $wpdb;

        $post_id = (int) $params['post_id'];
        $row = $wpdb->get_row( "SELECT latitude, longitude FROM {$wpdb->prefix}gmw_locations WHERE object_type = 'post' and object_id = '$post_id' LIMIT 1" );
        if ( null !== $row ) {
            $params['facet_value'] = $row->latitude;
            $params['facet_display_value'] = $row->longitude;
        }
    }
    return $params;
}, 10, 2 );