postgresql srid 4326 中 Postgis 中 2 点之间的距离（以米为单位）
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Distance between 2 POINTs in Postgis in srid 4326 in metres
提问by Rory
This is probably a simple question, but I'm not very good at PostGIS and don't fully grok all of this.
这可能是一个简单的问题，但我不太擅长 PostGIS，也没有完全理解所有这些。
Basically I have a table (nodes) with a POINT column (point). I have created an index on this column
基本上我有一个nodes带有 POINT 列 ( point)的表( )。我在此列上创建了索引
create index nodes__points on nodes using gist (point)
The column was created with
该列是用
select addgeometrycolumn('nodes', 'points', 'POINT', 4326, 2)
I am using srid 4326 because I'm adding data that's in the form (latitude, longitude). (i.e. the co-ordinate system where the position of Dublin, Ireland is lat=53.353 lon=-6.264 (which I've added with GeomFromText('POINT(-6.264 53.535)'))).
我正在使用 srid 4326，因为我正在添加形式为（纬度、经度）的数据。（即爱尔兰都柏林的坐标系 lat=53.353 lon=-6.264（我已添加GeomFromText('POINT(-6.264 53.535)')））。
For each point, I want to find all points that are roughly within a 1km box centred on that point (so selcet a.id, count(*) from nodes as a, nodes as b where SOME_DISTANCE_FUNCTION_HERE(a.point, b.point, 1000) group by a.id;. It doesn't have to be exact, just a rough hueristic figure. a 1km bbox is fine, a 1km circle is fine. It doesn't have to be exactly 1km, just that order of magnitude.
对于每个点，我想找到大约在以该点为中心的 1km 框内的所有点（因此selcet a.id, count(*) from nodes as a, nodes as b where SOME_DISTANCE_FUNCTION_HERE(a.point, b.point, 1000) group by a.id;。它不必非常精确，只是一个粗略的色调图。1km bbox 很好，1km 圆很好. 不一定要精确到 1 公里，只是这个数量级。
The ST_Distance/ST_DWithin/etc. all use the units of the SRID, which for 4326/WGS64 is degrees (so 1 = 1 degree of lattitude/longitude). But I want to use metres.
在ST_Distance/ST_DWithin的/ etc。都使用 SRID 的单位，对于 4326/WGS64，它是度数（所以 1 = 1 度纬度/经度）。但我想用米。
I tried ST_distance_sphereand st_dwithinwhich can use metres, but if I do that, the explainshows that the index isn't being used.
我试着ST_distance_sphere和st_dwithin它可以用米，但如果我这样做，explain是没有被使用显示了指数。
How can I get roughly what I want, anduse the geographical index?
我怎样才能大致得到我想要的东西，并使用地理索引？
UPDATE: This is on PostgreSQL 9.1 and PostGIS 2.0 svn build.
更新：这是在 PostgreSQL 9.1 和 PostGIS 2.0 svn 构建上。
采纳答案by Rory
Since writing this, I have discovered the "geographic" as opposed to the "geometry" type in PostGIS, which might do exactly what I want.
自从写这篇文章以来，我发现了 PostGIS 中的“地理”而不是“几何”类型，这可能正是我想要的。
回答by Francisco Valdez
You could use ST_Transform to use meters, also remeber that not all functions are available with geography types but if you really need speed use ST_DWithin, is the fastest way. Here's an aproximation of conversions between degrees and meters:
您可以使用 ST_Transform 来使用米，还请记住，并非所有功能都适用于地理类型，但如果您确实需要速度，请使用 ST_DWithin，这是最快的方法。这是度和米之间转换的近似值：
| places | degrees | distance |
| ------ | ---------- | -------- |
| 0 | 1.0 | 111 km |
| 1 | 0.1 | 11.1 km |
| 2 | 0.01 | 1.11 km |
| 3 | 0.001 | 111 m |
| 4 | 0.0001 | 11.1 m |
| 5 | 0.00001 | 1.11 m |
| 6 | 0.000001 | 0.111 m |
| 7 | 0.0000001 | 1.11 cm |
| 8 | 0.00000001 | 1.11 mm |
回答by jr from Yaoundé
Old question but you just have to cast like this: ST_Distance(p.geom::geography, u.geom::geography)where p and u are alias for two tables
老问题，但你只需要像这样转换：ST_Distance(p.geom::geography, u.geom::geography)其中 p 和 u 是两个表的别名
