PHP -函数正常工作，直到我尝试使用while循环和数据库来定义输入变量。

Question

基本上，我试图找出一个特定的“中心城市”与该州所有其他城市之间的距离(以英里为单位)。所以我取一个城市，找出这一个城市和多个城市之间的多个距离。

我使用Haversine函数，当我简单地给每个变量分配一个纬度和经度时，它会产生正确的结果，如下所示。然而，当我从数据库中检索到多纬度和经度时，距离结果从0到300范围到4,500-5,000范围非常接近。

//Works as it should

$center_lat = 30.332184;
$center_lng = -81.655651;

$lat = 29.901244;
$lng = -81.312434;

function haversineGreatCircleDistance(
                                      $latitudeFrom, $longitudeFrom, $latitudeTo, $longitudeTo, $earthRadius = 3961000)
{
    // convert from degrees to radians
    $latFrom = deg2rad($latitudeFrom);
    $lonFrom = deg2rad($longitudeFrom);
    $latTo = deg2rad($latitudeTo);
    $lonTo = deg2rad($longitudeTo);

    $latDelta = $latTo - $latFrom;
    $lonDelta = $lonTo - $lonFrom;

    $angle = 2 * asin(sqrt(pow(sin($latDelta / 2), 2) +
                           cos($latFrom) * cos($latTo) * pow(sin($lonDelta / 2), 2)));
    return $angle * $earthRadius;
}

$distance = haversineGreatCircleDistance($center_lat, $center_lng, $lat, $lng, 3961);
print($distance) . "<br/><br/>"; 

// The output should be between 35-36

下面是我的代码--问题似乎来自于第二个SQL查询或while循环：

// This first section works - I also have an input form to get the $_POST['state'] and $_POST['city'] which works fine

if($_SERVER["REQUEST_METHOD"] == "POST") {
    $state = $_POST['state'];
    $city = $_POST['city'];

    $sql = "SELECT DISTINCT lat, lon FROM foodtruck_user WHERE city = '$city' AND state = '$state' LIMIT 1";

    $result = mysqli_query($connection, $sql);
    while($row = mysqli_fetch_array($result)) {
        echo $row['lat'] . "<br/>"; 
        echo $row['lon'] . "<br/><br/>";  
        $center_lat = $row['lat'];
        $center_lng = $row['lon'];
    }

    // Below is where the I am having the issue...the output from "echo" is accurate, but the calculated $distance is very wrong.

    $sql2 = "SELECT DISTINCT lat, lon, city FROM foodtruck_user WHERE state = '$state'";
    $result2 = mysqli_query($connection, $sql2);
    while($row2 = mysqli_fetch_array($result2)) {
        if(!empty($row2['lat']) && !empty($row2['lon']) && !empty($row2['city'])){
            echo "Lat: " . $row2['lat'] . " Lon: " . $row2['lon'] . " City: " . $row2['city'] . " center_lat: " . $center_lat . " center_lng: " . $center_lng . " Distance: ";
            $lat = $row2['lat'];
            $lon = $row2['lon'];
            $distance = haversineGreatCircleDistance($center_lat, $center_lng, $lat, $lng, 3961);
            print($distance) . "<br/><br/>"; 
        }
    }   
}

下面是一些例子，说明browser...everything中的输出是正确的，除了“距离”--这是我的question...why --变量被精确地回显，但是函数的结果是不准确的？

30.329882
-81.651672

Lat: 30.329882 Lon: -81.651672 City: Jacksonville center_lat: 30.329882 center_lng: -81.651672 Distance: 4749.7501036981 // distance should be 0
Lat: 27.961381 Lon: -82.45972 City: Tampa center_lat: 30.329882 center_lng: -81.651672 Distance: 4816.3124301703
Lat: 26.231529 Lon: -80.12346 City: Pompano Beach center_lat: 30.329882 center_lng: -81.651672 Distance: 4866.2490051465
Lat: 26.113536 Lon: -80.224272 City: Plantation center_lat: 30.329882 center_lng: -81.651672 Distance: 4869.6942811343
Lat: 28.539882 Lon: -81.372668 City: Orlando center_lat: 30.329882 center_lng: -81.651672 Distance: 4799.8575314421
Lat: 26.51747 Lon: -80.083427 City: Boynton Beach center_lat: 30.329882 center_lng: -81.651672 Distance: 4857.9202539164
Lat: 26.249221 Lon: -80.211483 City: Margate center_lat: 30.329882 center_lng: -81.651672 Distance: 4865.7328403355

Answer 1

在调用函数时，您使用了$lng而不是$lon，而$lon没有定义，因此它被传递为0--导致计算不准确。抄录自上：

$lon = $row2['lon'];
$distance = haversineGreatCircleDistance($center_lat, $center_lng, $lat, $lng, 3961);

打字，伙计。打字。