用 SQLite 计算大圆距离

问题描述

这是我的问题，我有一个包含位置和纬度/经度的 SQLite 表.基本上我需要:

Here is my problem, I have a SQLite table with locations and latitudes / longitudes. Basically I need to:

SELECT location, HAVERSINE(lat, lon) AS distance FROM location ORDER BY distance ASC;

HAVERSINE() 是一个 PHP 函数，它应该返回 大圆距离(以英里或公里为单位)给定一对纬度和经度值.其中一对应由 PHP 提供，另一对应由 locations 表中的每个纬度/经度行提供.

HAVERSINE() is a PHP function that should return the Great-Circle Distance (in miles or km) given a pair of latitude and longitude values. One of these pairs should be provided by PHP and the other pair should be provided by each latitude / longitude row available in the locations table.

因为 SQLite 没有任何地理空间扩展 (AFAIK SpatiaLite 存在，但仍然......) 我猜最好的方法是将自定义函数与 PDO 方法之一一起使用:

Since SQLite doesn't has any Geo Spatial extension (AFAIK SpatiaLite exists but still...) I'm guessing the best approach would be to use a custom function with either one of the PDO methods:

• PDO::sqliteCreateFunction()
• PDO::sqliteCreateAggregate()

我认为对于这种情况 PDO::sqliteCreateFunction() 就足够了，但是我对这个函数的有限经验可以简化为类似于 PHP 手册中提供的用例:

I think for this case PDO::sqliteCreateFunction() would be enough, however my limited experience with this function can be reduced to usage cases similar to the one provided in the PHP Manual:

$db = new PDO('sqlite:geo.db');

function md5_and_reverse($string) { return strrev(md5($string)); }

$db->sqliteCreateFunction('md5rev', 'md5_and_reverse', 1);
$rows = $db->query('SELECT md5rev(filename) FROM files')->fetchAll();

我在弄清楚如何让 SQLite 用户定义函数同时处理来自 PHP 和表数据的数据时遇到了一些麻烦，如果有人能帮我解决这个问题，我将不胜感激问题，同时也更好地理解 SQLite UDF(SQLite IMO 的一大胜利).

I'm having some trouble figuring out how can I get an SQLite user defined function to process data from PHP and table data at the same time and I would appreciate if someone could help me solve this problem while also understanding SQLite UDFs (a big win of SQLite IMO) a little bit better.

提前致谢！

推荐答案

来自您的有趣链接".

function sqlite3_distance_func($lat1,$lon1,$lat2,$lon2) {
    // convert lat1 and lat2 into radians now, to avoid doing it twice below
    $lat1rad = deg2rad($lat1);
    $lat2rad = deg2rad($lat2);
    // apply the spherical law of cosines to our latitudes and longitudes, and set the result appropriately
    // 6378.1 is the approximate radius of the earth in kilometres
    return acos( sin($lat1rad) * sin($lat2rad) + cos($lat1rad) * cos($lat2rad) * cos( deg2rad($lon2) - deg2rad($lon1) ) ) * 6378.1;
}

$db->sqliteCreateFunction('DISTANCE', 'sqlite3_distance_func', 4);

然后进行查询:

"SELECT * FROM location ORDER BY distance(latitude,longitude,{$lat},{$lon}) LIMIT 1"

<小时>

编辑(按 QOP):我终于再次需要这个，这个解决方案效果很好，我只是稍微修改了代码，让它不那么冗长，并且可以处理非数字值优雅地，这里是:

EDIT (by QOP): I finally needed this again and this solution worked out great, I just ended up modifying the code a bit to it is a bit less verbose and handles non-numeric values gracefully, here it is:

$db->sqliteCreateFunction('distance', function () {
    if (count($geo = array_map('deg2rad', array_filter(func_get_args(), 'is_numeric'))) == 4) {
        return round(acos(sin($geo[0]) * sin($geo[2]) + cos($geo[0]) * cos($geo[2]) * cos($geo[1] - $geo[3])) * 6378.14, 3);
    }

    return null;
}, 4);

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