[英]Distance between 2 POINTs in Postgis in srid 4326 in metres
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,但我不是很擅长PostGIS,也没有完全理解这一切。
Basically I have a table ( nodes
) with a POINT column ( point
). 基本上我有一个带有POINT列(
point
)的表( nodes
)。 I have created an index on this column 我在这个专栏上创建了一个索引
create index nodes__points on nodes using gist (point)
The column was created with 该列是用。创建的
select addgeometrycolumn('nodes', 'points', 'POINT', 4326, 2)
I am using srid 4326 because I'm adding data that's in the form (latitude, longitude). 我正在使用srid 4326,因为我正在添加形式(纬度,经度)的数据。 (ie 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)')
)). (即爱尔兰都柏林的位置= 53.353 lon = -6.264的坐标系统(我已经使用
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,我想找到大致位于该点中心的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;
.它不一定是精确的,只是一个粗略的人文形象.1km的bbox很好,1km的圆很好。它不一定是1km,只是那个顺序数量级。
The ST_Distance
/ ST_DWithin
/etc. ST_Distance
/ ST_DWithin
/ ST_DWithin
all use the units of the SRID, which for 4326/WGS64 is degrees (so 1 = 1 degree of lattitude/longitude). 所有都使用SRID的单位,4326 / WGS64是度(因此1 = 1度的纬度/经度)。 But I want to use metres.
但我想用米。
I tried ST_distance_sphere
and st_dwithin
which can use metres, but if I do that, the explain
shows that the index isn't being used. 我尝试了
ST_distance_sphere
和st_dwithin
,可以使用米,但如果我这样做, explain
显示索引没有被使用。
How can I get roughly what I want, and use 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。
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. 您可以使用ST_Transform来使用仪表,还要记住并非所有功能都可用于地理类型,但如果您真的需要速度使用ST_DWithin,则是最快的方法。 Here's an aproximation of conversions between degrees and meters:
这是度数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 |
自写这篇文章以来,我发现了“地理”而不是PostGIS中的“几何”类型,它可能完全符合我的要求。
老问题,但你只需要像这样: ST_Distance(p.geom::geography, u.geom::geography)
其中p和u是两个表的别名
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