从GPS坐标组中获取最大距离

Question

因此，我有一个包含多行GPS坐标的数据库。我知道如何计算给定经纬度与数据库中任何经纬度之间的距离，但是我要做的基本上是查看一组行的坐标，并获得相距最远的两行。如果可以在SQL中执行此操作，我会很喜欢，但是如果必须在可以使用的应用程序代码中执行此操作，我就会喜欢它。这是我要计算两点之间的距离的操作：

ROUND(( 3960 * acos( cos( radians( :lat ) ) *
cos( radians( p.latitude ) ) * cos( radians(  p.longitude  ) - radians( :lng ) ) +
sin( radians( :lat ) ) * sin( radians(  p.latitude  ) ) ) ),1) AS distance

我们正在尝试做的是，查看特定用户的GPS数据，并确保他们在全国范围内没有活动。用户的所有坐标彼此之间的距离应在几英里以内。如果坐标在全国范围内，则表明我们的系统中存在恶意活动。因此，我希望能够快速浏览特定用户的数据，并知道他们的最大距离是多少。

我考虑过只在经纬度上分别运行最大/最小，并为可接受的范围设置内部阈值。也许这比较容易，但是如果我在第一部分中提出的要求是可能的，那将是最好的。

Answer 1

如果您有 SQL Server 2008 或更高版本，则可以使用 GEOGRAPHY 来计算距离，例如：

DECLARE @lat1 DECIMAL(19,6) = 44.968046;
DECLARE @lon1 DECIMAL(19,6) = -94.420307;
DECLARE @lat2 DECIMAL(19,6) = 44.33328;
DECLARE @lon2 DECIMAL(19,6) = -89.132008;
SELECT GEOGRAPHY::Point(@lat1, @lon1, 4326).STDistance(GEOGRAPHY::Point(@lat2, @lon2, 4326));

这使得问题变得微不足道？

对于用户的一组纬度/经度，您需要计算每组之间的距离，然后返回最大距离。将所有这些放在一起，您可能可以执行以下操作：

DECLARE @UserGPS TABLE (
    UserId INT, --the user
    GPSId INT, --the incrementing unique id associated with this GPS reading (could link to a table with more details, e.g. time, date)
    Lat DECIMAL(19,6), --lattitude
    Lon DECIMAL(19,6)); --longitude
INSERT INTO @UserGPS SELECT 1, 1, 44.968046, -94.420307; --User #1 goes on a very long journey
INSERT INTO @UserGPS SELECT 1, 2, 44.33328, -89.132008;
INSERT INTO @UserGPS SELECT 1, 3, 34.12345, -92.21369;
INSERT INTO @UserGPS SELECT 1, 4, 44.978046, -94.430307;
INSERT INTO @UserGPS SELECT 2, 1, 44.968046, -94.420307; --User #2 doesn't get far
INSERT INTO @UserGPS SELECT 2, 2, 44.978046, -94.430307;

--Make a working table to store the distances between each set of co-ordinates
--This isn't strictly necessary; we could change this into a common-table expression
DECLARE @WorkTable TABLE (
    UserId INT, --the user
    GPSIdFrom INT, --the id of the first set of co-ordinates
    GPSIdTo INT, --the id of the second set of co-ordinates being compared
    Distance NUMERIC(19,6)); --the distance

--Get the distance between each and every combination of co-ordinates for each user
INSERT INTO
    @WorkTable
SELECT
    c1.UserId,
    c1.GPSId,
    c2.GPSId,
    GEOGRAPHY::Point(c1.Lat, c1.Lon, 4326).STDistance(GEOGRAPHY::Point(c2.Lat, c2.Lon, 4326))
FROM
    @UserGPS c1
    INNER JOIN @UserGPS c2 ON c2.UserId = c1.UserId AND c2.GPSId > c1.GPSId;
--Note this is a self-join, but single-tailed.  So we compare each set of co-ordinates to each other set of co-ordinates for a user
--This is handled by the "c2.GPSID > c1.GPSId" in the JOIN clause
--As an example, say we have three sets of co-ordinates for a user
--We would compare set #1 to set #2
--We would compare set #1 to set #3
--We would compare set #2 to set #3
--We wouldn't compare set #3 to anything (as we already did this)

--Determine the maximum distance between all the GPS co-ordinates per user
WITH MaxDistance AS (
    SELECT
        UserId,
        MAX(Distance) AS Distance
    FROM
        @WorkTable
    GROUP BY
        UserId)
--Report the results
SELECT
    w.UserId,
    g1.GPSId,
    g1.Lat,
    g1.Lon,
    g2.GPSId,
    g2.Lat,
    g2.Lon,
    md.Distance AS MaxDistance
FROM 
    MaxDistance md
    INNER JOIN @WorkTable w ON w.UserId = md.UserId AND w.Distance = md.Distance
    INNER JOIN @UserGPS g1 ON g1.UserId = md.UserId AND g1.GPSId = w.GPSIdFrom
    INNER JOIN @UserGPS g2 ON g2.UserId = md.UserId AND g2.GPSId = w.GPSIdTo;

结果是：

UserId  GPSId   Lat Lon GPSId   Lat Lon MaxDistance
1   3   34.123450   -92.213690  4   44.978046   -94.430307  1219979.460185
2   1   44.968046   -94.420307  2   44.978046   -94.430307  1362.820895

现在，我对您所持有的数据做了很多假设，因为您的问题中没有有关详细信息的信息。您可能需要在某种程度上对此进行调整？