项目需求，要根据用户经纬度计算之间距离整理：

1. sql 查询  2000米之内的宝贝信息

let sql = `SELECT b.user_id, c.id as cowry_id, c.type, c.latitude, c.longitude, u.nickname, u.avatar, u.uuid,    

    (    
        convert(

            6371 * acos (    

                cos ( radians(:latitude) )    

                * cos( radians( c.latitude ) )    

                * cos( radians( c.longitude ) - radians(:longitude) )    

                + sin ( radians(:latitude) )    

                * sin( radians( c.latitude ) )    

            ), decimal(10,2)

        )

    ) AS distance    

    FROM cowry as c

    left join cowryBuryUser as b on c.id = b.cowry_id   

    left join user as u on b.user_id = u.id

    WHERE c.type = :type

    AND c.status = 0

    HAVING distance < 2    //小于 2000 米 内的数据

    ORDER BY distance   

    LIMIT 0 , 20;`

    let res = await Sequelize.query(sql, {

        replacements: {

            latitude: latitude,

            longitude: longitude,

            user_id: user_id,

            type: type

        },
        type: Sequelize.QueryTypes.SELECT

    })

2. 计算两个经纬度之间的距离 

exports.getDistance = function (lat1, lng1, lat2, lng2) {

    if (isNaN(lat1) || isNaN(lng1) || isNaN(lat2) || isNaN(lng2) || lat1 == null || lng1 == null || lat2 == null || lng2 == null) {

       return '未知'

    }

    let EARTH_RADIUS = 6378.137

    let radLat1 = lat1 * Math.PI / 180.0  // 角度转弧度

    let radLat2 = lat2 * Math.PI / 180.0

    let latDistance = radLat1 - radLat2

    let lngDistance = (lng1 * Math.PI / 180.0) - (lng2 * Math.PI / 180.0)

    // 反正弦+余弦

    let distance = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(latDistance / 2), 2) +

        Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(lngDistance / 2), 2)))

    distance = distance * EARTH_RADIUS

    distance = Math.round(distance * 1000)  //米

    return distance

}

3. 根据某一个经纬度获取范围内的最大最小经纬度范围

/***  
* 根据当前经纬度获取一定范围内的两个经纬度值 经纬度最大或最小  
* @param meter     范围 千米  
* @param lng       经度  
* @param lat       纬度  
* @returns {{maxLat: string, minLat: string, maxLng: string, minLng: string}}  
*/

exports.getLaLon = function (meter, lng, lat) {

    let EARTH_RADIUS = 6378.137

    let range = 180 / Math.PI * meter / EARTH_RADIUS  //这里计算出来是千米

    let lngR = range / Math.cos(lat * Math.PI / 180)

    let maxLat = parseFloat(lat) + range; //最大纬度

    let minLat = parseFloat(lat) - range;  //最小纬度

    let maxLng = parseFloat(lng) + lngR;   //最大经度

    let minLng = parseFloat(lng) - lngR;   //最小经度

    return {

        maxLat: maxLat.toFixed(7),

        minLat: minLat.toFixed(7),

        maxLng: maxLng.toFixed(7),

        minLng: minLng.toFixed(7)

    }

}