根据纬度和经度获取半径范围内的拉链码

Question

I am trying to get zipcodes within a radius of 160km of the provided latitude/longitude coordinates. I already have a database of zipcodes, latitudes & longitudes, my problem is calculate the radius.

I have been looking at examples of how to do this, and this is what I came up with. But evidently something is wrong, because I'm getting distances that are ~9000km away according to the $dist variable.

public function getClose($latitude, $longitude) {
    $latitudes  = [floor($latitude)-2, ceil($latitude)+2];
    $locations  = Zipcode::whereBetween('latitude', $latitudes)->get();

    foreach ($locations as $location) {
        $venueLat = $location->latitude;
        $venueLng = $location->longititude;

        $latDistance = deg2rad($latitude - $venueLat);
        $lngDistance = deg2rad($longitude - $venueLng);
        $a = (sin($latDistance / 2) * sin($latDistance / 2)) + (cos(deg2rad($latitude))) * (cos(deg2rad($venueLat))) * (sin($lngDistance / 2)) * (sin($lngDistance / 2));
        $c = 2 * atan2(sqrt($a), sqrt(1 - $a));

        // Distance between 2 points in km. 6371 = Earths radius
        $dist = 6371 * $c;
        var_dump($dist); // This is the line saying it's about 9000km away

        if ($dist < 160){
            var_dump($location->zip);
        }
    }
}

That code was mostly based on this answer on a related question: https://stackoverflow.com/a/18465217

But, obviously something didn't translate right, or I misunderstood something. Any help would be vastly appreciated!

Answer 1

Here is the code that I ended up using that works. A couple things changed, but the biggest difference is the formula. As you can see they're significantly different. I'm not very good at math, so I don't really know what the differences are, but I do know this one works.

public function getClose($latitude, $longitude) {
    $latitudes  = [floor($latitude)-2, ceil($latitude)+2];
    $longitudes = [floor($longitude)-1, ceil($longitude)+1];
    $locations  = Zipcode::whereBetween('latitude', $latitudes)->whereBetween('longitude', $longitudes)->get();
    $zips       = [];

    foreach ($locations as $location) {
        $theta = $longitude - $location->longitude;
        $dist = sin(deg2rad($latitude)) * sin(deg2rad($location->latitude)) +  cos(deg2rad($latitude)) * cos(deg2rad($location->latitude)) * cos(deg2rad($theta));
        $dist = acos($dist);
        $dist = rad2deg($dist);
        $miles = $dist * 60 * 1.1515;

        if ($miles <= 100){
            $zips[] = $location->zip;
        }
    }
}