Selecting location within range

Goodday,

I'm trying to do the following:

Search locations within a range of a certain point based on latitude and longitude. I got this working going through the list of points and calculate the distance to the point. Then i filter them by distance to find the locations within the range.

part of the script:

  $lat1 = deg2rad($postcode->latitude);
                        $lon1 = deg2rad($postcode->longitude);
                        $lat2 = deg2rad(floatval($latitude));
                        $lon2 = deg2rad(floatval($longitude));
    
                        $delta_lat = $lat2 - $lat1;
                        $delta_lng = $lon2 - $lon1;
    
                        $hav_lat = (sin($delta_lat / 2))**2;
                        $hav_lng = (sin($delta_lng / 2))**2;
    
                        $distance = 2 * asin(sqrt($hav_lat + cos($lat1) * cos($lat2) * $hav_lng));
    
                        $earth_radius_km = 6371.009;
    
                        $actual_distance = $earth_radius_km * $distance;

But now i want to find the zip codes near a point. Also based on latitude and longitude. But now we got almost 50.000 zip codes. I don't want to use the method above because i then have to go through all zip codes and calculate the distance. A process whats costs a lot of serverpower.

I'am wondering if there is way to pre select zipcodes who could be in the range. So i can first select the zipcodes where i can be useful to calculate the distance. Then i can run those zip codes through the way i described above.

Anyone any tips for this?

thanks in advance.