Get distance from lat and long

search-proximity.php

<?php 
/**
 * Get the SQL query for getting listings within a given proximity.
 *
 * @link  https://wordpress.stackexchange.com/a/206560/123815
 * @since 1.0.0
 */
public function get_proximity_sql() {
	global $wpdb;

	return "
	SELECT $wpdb->posts.ID,
		( %s * acos(
			cos( radians(%s) ) *
			cos( radians( latitude.meta_value ) ) *
			cos( radians( longitude.meta_value ) - radians(%s) ) +
			sin( radians(%s) ) *
			sin( radians( latitude.meta_value ) )
		) )
		AS distance, latitude.meta_value AS latitude, longitude.meta_value AS longitude
		FROM $wpdb->posts
		INNER JOIN $wpdb->postmeta
			AS latitude
			ON $wpdb->posts.ID = latitude.post_id
		INNER JOIN $wpdb->postmeta
			AS longitude
			ON $wpdb->posts.ID = longitude.post_id
		WHERE 1=1
			AND ($wpdb->posts.post_status = 'publish' )
			AND latitude.meta_key='geolocation_lat'
			AND longitude.meta_key='geolocation_long'
		HAVING distance < %s
		ORDER BY distance ASC";
}




$proximity = absint( $form_data['proximity'] );
$location = isset($form_data['search_location']) ? sanitize_text_field( stripslashes( $form_data['search_location'] ) ) : false;
$lat = (float) $form_data['search_location_lat'];
$lng = (float) $form_data['search_location_lng'];
$units = isset($form_data['proximity_units']) && $form_data['proximity_units'] == 'mi' ? 'mi' : 'km';

if ( $lat && $lng && $proximity && $location ) {
	// dump($lat, $lng, $proximity);

	$earth_radius = $units == 'mi' ? 3959 : 6371;

	$sql = $wpdb->prepare( $this->get_proximity_sql(), $earth_radius, $lat, $lng, $lat, $proximity );

	// dump($sql);

	$post_ids = (array) $wpdb->get_results( $sql, OBJECT_K );

	if (empty($post_ids)) $post_ids = ['none'];

	$args['post__in'] = array_keys( (array) $post_ids );

	// Remove search_location filter when using proximity filter.
	$args['search_location'] = '';
}