How to implement search for nearby people in php

php method to implement search for nearby people: first declare a function to calculate the range of longitude and latitude; then find all records that meet the conditions within this longitude and latitude range from the database; finally query the longitude and latitude in "$radius "The detailed addresses of power stations within the range are sufficient.

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A recent project requires querying people within ten kilometers of the user based on the longitude and latitude of the user's current location. This function is not a very technical implementation (of course, we only refer to the When the function itself and the amount of data are small, it does not include other problems derived from it for a long time), but due to various considerations, I decided to record it.

In the future, whether we are engaged in APP server development or WEB development, customers may often ask for such functions, so we still need to master its principles.

[Problem Raising]

How should we think about this problem? Some friends may want to say: "Now that we already know the longitude and latitude of the current user, we query the user's longitude and latitude from the database, and then calculate them one by one to filter out all qualified users."

我I once took it for granted, without taking into account the feelings of the database. When you are operating a database of one hundred thousand or one million levels, the problems caused by such an approach will be catastrophic. So what should we do? Woolen cloth?

[Implementation Ideas]

First of all, we should think like this: Now that we know the longitude and latitude of the user's current location and the range we are going to search, can we calculate a range? That is to say, based on a center point and radius, calculate the maximum and minimum values ​​of longitude and latitude that meet the conditions.

[Specific Implementation]

So here, friends who want to think independently and complete it, don’t read any further.

We mentioned an implementation principle of this function above, and then we will explain the specific implementation steps.

We first declare a function to calculate the range of latitude and longitude:

/**
 * 根据经纬度和半径计算出范围
 * @param string $lat 纬度
 * @param String $lng 经度
 * @param float $radius 半径
 * @return Array 范围数组
 */private function calcScope($lat, $lng, $radius) {
    $degree = (24901*1609)/360.0;    $dpmLat = 1/$degree;    $radiusLat = $dpmLat*$radius;    $minLat = $lat - $radiusLat;       // 最小纬度
    $maxLat = $lat + $radiusLat;       // 最大纬度

    $mpdLng = $degree*cos($lat * (PI/180));    $dpmLng = 1 / $mpdLng;    $radiusLng = $dpmLng*$radius;    $minLng = $lng - $radiusLng;      // 最小经度
    $maxLng = $lng + $radiusLng;      // 最大经度

    /** 返回范围数组 */
    $scope = array(        'minLat'    =>  $minLat,        'maxLat'    =>  $maxLat,        'minLng'    =>  $minLng,        'maxLng'    =>  $maxLng
        );    return $scope;
}

The returned array contains the maximum and minimum latitude and longitude that meet the conditions within the $radius range.

Now that we have obtained the range, we can start to search from the database for all records that meet the conditions within this longitude and latitude range:

/**
 * 根据经纬度和半径查询在此范围内的所有的
 * @param  String $lat    纬度
 * @param  String $lng    经度
 * @param  float $radius 半径
 * @return Array         计算出来的结果
 */public function searchByLatAndLng($lat, $lng, $radius) {
    $scope = $this->calcScope($lat, $lng, $radius);     // 调用范围计算函数，获取最大最小经纬度
    /** 查询经纬度在 $radius 范围内的电站的详细地址 */
    $sql = &#39;SELECT `字段` FROM `表名` WHERE `Latitude` < &#39;.$scope[&#39;maxLat&#39;].&#39; and `Latitude` > &#39;.$scope[&#39;minLat&#39;].&#39; and `Longitude` < &#39;.$scope[&#39;maxLng&#39;].&#39; and `Longitude` > &#39;.$scope[&#39;minLng&#39;];    $stmt = self::$db->query($sql);    $res = $stmt->fetchAll(PDO::FETCH_ASSOC);       // 获取查询结果并返回
    return $res;
}

[Extended]

Until Now, we already know how to calculate nearby people, but in actual needs, we often need to calculate the actual distance of each person from the current center point.

Next, let’s look at a method:

/**
 * 获取两个经纬度之间的距离
 * @param  string $lat1 纬一
 * @param  String $lng1 经一
 * @param  String $lat2 纬二
 * @param  String $lng2 经二
 * @return float  返回两点之间的距离 */public function calcDistance($lat1, $lng1, $lat2, $lng2) {    /** 转换数据类型为 double */
    $lat1 = doubleval($lat1);    $lng1 = doubleval($lng1);    $lat2 = doubleval($lat2);    $lng2 = doubleval($lng2);    /** 以下算法是 Google 出来的，与大多数经纬度计算工具结果一致 */
    $theta = $lng1 - $lng2;    $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));    $dist = acos($dist);    $dist = rad2deg($dist);    $miles = $dist * 60 * 1.1515;    return ($miles * 1.609344);
}

We have previously calculated the longitude and latitude of all nearby people who meet the conditions, then we can combine each person’s longitude and latitude with the current center point The longitude and latitude are passed into the function as parameters, and the distance between each qualified person and the center point is finally calculated.

In order to ensure the rigor of the program, I must make the following explanation:

The calculation method of the latitude and longitude range was found on Baidu. There is currently no standard calculation tool found, so this algorithm Unable to verify, but most posts basically use this calculation method.

The calculation method of latitude and longitude distance was found on Google, and the calculation results are similar to those of most calculation tools. The reason why I searched in Google was because I had searched for various calculation methods on Baidu, but the results were not satisfactory.
When calculating the range through radius and latitude and longitude, the unit of radius is m; when calculating distance, the result is km. Therefore, be aware of unit changes.
I am still trying to verify and seek professional help to obtain more accurate calculation results.

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