SQL Server Geography数据类型在线上最近的点 [英] SQL Server Geography datatype nearest point on line

问题描述

我正在尝试建立查询，但是遇到了一些困难.

I am trying to build a query, but I am having some difficulty.

我有一个SQL Server 2008数据库，该数据库的表除其他字段外还包含描述路段的地理字段. (此数据是从美国人口普查的TIGER/Line数据中导入的.)

I have a SQL Server 2008 database with a table that includes, among other fields, a geography field that describes road segments. (This data has been imported from TIGER/Line data from the U.S. Census.)

我还有一个描述用户位置的固定点.我想在数据库中找到最接近这一点的路段，但似乎无法弄清楚该如何完成.此外，我想找到该段上与用户位置点最接近的点.这就是我要选择的内容并返回我的查询.

I have another fixed point describing a user's location. I want to find the closest road segment in the database to that point, but I can't seem to figure out how to accomplish this. Furthermore, I want to find the closest point on that segment to the user location point. This is what I want to select and return back in my query.

有人对可以帮助我的地理/几何功能有任何经验吗?

Does anyone have any experience with the geography/geometry functionality that can help me?

谢谢！

推荐答案

您可以将对象存储在GEOGRAPHY列中，并在此列上创建SPATIAL INDEX.

You can store your objects in a GEOGRAPHY column and create a SPATIAL INDEX over this column.

不幸的是，SQL Server通过平铺表面并将图块标识符存储在普通的B-Tree索引中来实现空间索引，因此普通的ORDER BY STDistance将不起作用(嗯，它可以工作，但不会使用索引).

Unfortunately, SQL Server implements spatial indexes by tiling the surface and storing the tile identifiers in a plain B-Tree index, so plain ORDER BY STDistance won't work (well, it will work but won't use the index).

相反，您必须进行与此类似的查询:

Instead, you'll have to make a query similar to this:

DECLARE @mypoint GEOGRAPHY
SET @mypoint = geography::STGeomFromText('POINT(@mylat, @mylon)', 4326);

WITH    num (distance) AS
        (
        SELECT  1000
        UNION ALL
        SELECT  distance + 1000
        FROM    num
        WHERE   distance <= 50000
        )
SELECT  TOP 1 m.*
FROM    num
CROSS APPLY
        (
        SELECT  TOP 1 *
        FROM    mytable
        WHERE   myroad.STDistance(@mypoint) <= distance
        ORDER BY
                STDistance(@mypoint)
        ) m

这样，SQL Server会先使用索引在距您的点1公里以内的道路上搜索，然后在2公里以内等地方搜索道路.

This way, SQL Server will first search roads within 1 kilometer from your point, then within 2 kilometers, etc., each time using the index.

更新:

如果表中有多个点，并希望找到每个点的最近点:

If you have multiple points in a table and want to find the closest point for each of them:

WITH    num (distance) AS
        (
        SELECT  1000
        UNION ALL
        SELECT  distance + 1000
        FROM    num
        WHERE   distance <= 50000
        )
SELECT  mp.mypoint, m.*
FROM    @mypoints mp
CROSS APPLY
        (
        SELECT  TOP 1 m.*
        FROM    num
        CROSS APPLY
                (
                SELECT  TOP 1 *
                FROM    mytable
                WHERE   myroad.STDistance(@mypoint) <= distance
                ORDER BY
                        STDistance(@mypoint)
                ) m
        ) m

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