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[英]How to get the Nth LineString from a MultiLineString in PostGIS?
[英]How to aggregate multiple points by two columns and create a LineString / MultiLineString out of them
我有一个名为locations的表,其中包含以下行:
id uuid NOT NULL,
"deviceId" text COLLATE pg_catalog."default",
"userId" uuid,
"userName" text COLLATE pg_catalog."default",
"creationDateTime" timestamp with time zone,
shape geometry,
CONSTRAINT id PRIMARY KEY (id)
想象一下,我的用户每小时将点数注册到该表的shape
列中。当注册该点的时间并注册到表中时,将其保存到creationDateTime
列中,如下所示: 2018-08-22 00:03:41.649+04:30
。
我如何提取此信息:
each User ---- each day ---- list of geometry(shape column)
例如each User ---- each day ---- list of geometry(shape column)
:
第一天的User1包含几何点列表。 第二天的User1包含几何点列表等等。
我通过mongo对同一项目进行了此查询:
{$project: {
_id: 0,
uId : "$UserId",
dId : "$DeviceId",
ts :"$CreationDateTime",
point : "$Point"
}
},
{$group: {
_id :{
did: "$dId",
day: { $dayOfMonth: "$ts" }
},
docs: { $push: "$$ROOT" }
}
},
{
$sort:{"_id.day": -1}
}
但是我怎么用postgresql做到这一点? 在postgre上不存在这种聚合,而在postgresql上我是新来的。 这是我的查询:
(Select test1."deviceId",test1."shape", test1."creationDateTime" From
(Select * from locations) as test1 Group By test1."deviceId",test1."shape",test1."creationDateTime"
ORDER BY test1."creationDateTime")
此查询不适合结果,我知道此查询有问题。 用户的deviceId经常与其他行重复出现。我该如何处理?
最后,我想为per user - per day - multi poly line
创建多折线per user - per day - multi poly line
可能有上百万种方法可以回答这个问题。 这是其中之一:
考虑你的表结构..
CREATE TEMPORARY TABLE locations
(id uuid,
deviceId text COLLATE pg_catalog."default",
userId uuid,
userName text COLLATE pg_catalog."default",
creationDateTime timestamp with time zone,
shape geometry);
..以及这些样本数据..
INSERT INTO locations (userId, creationDateTime, shape)
VALUES ('d1166a84-ab66-11e8-98d0-529269fb1459',CURRENT_DATE,'POINT(-1.25 51.75)'),
('d1166a84-ab66-11e8-98d0-529269fb1459',CURRENT_DATE,'POINT(-1.15 52.96)'),
('d1166a84-ab66-11e8-98d0-529269fb1459',CURRENT_DATE,'POINT(-0.13 50.82)'),
('d1166a84-ab66-11e8-98d0-529269fb1459',CURRENT_DATE-1,'POINT(-2.22 53.48)'),
('d1166a84-ab66-11e8-98d0-529269fb1459',CURRENT_DATE-1,'POINT(-0.11 51.51)');
..您可以汇总每个用户+日期的积分,并使用ST_MakeLine
和GROUP BY
创建LINESTRING
:
SELECT userId, creationDateTime, ST_AsText(ST_MakeLine(shape))
FROM locations
GROUP BY userId, creationDateTime
ORDER BY creationDateTime;
userid | creationdatetime | st_astext
--------------------------------------+------------------------+-------------------------------------------------
d1166a84-ab66-11e8-98d0-529269fb1459 | 2018-08-28 00:00:00+02 | LINESTRING(-2.22 53.48,-0.11 51.51)
d1166a84-ab66-11e8-98d0-529269fb1459 | 2018-08-29 00:00:00+02 | LINESTRING(-1.25 51.75,-1.15 52.96,-0.13 50.82)
(2 Zeilen)
用户d1166a84-ab66-11e8-98d0-529269fb1459
在2018-08-28 00:00:00+02
图形化显示
您可以通过相同的方式使用ST_Collect
创建MULTIPOINT
:
SELECT userId, creationDateTime, ST_AsText(ST_Collect(shape))
FROM locations
GROUP BY userId, creationDateTime
ORDER BY creationDateTime;
userid | creationdatetime | st_astext
--------------------------------------+------------------------+-------------------------------------------------
d1166a84-ab66-11e8-98d0-529269fb1459 | 2018-08-28 00:00:00+02 | MULTIPOINT(-2.22 53.48,-0.11 51.51)
d1166a84-ab66-11e8-98d0-529269fb1459 | 2018-08-29 00:00:00+02 | MULTIPOINT(-1.25 51.75,-1.15 52.96,-0.13 50.82)
(2 Zeilen)
编辑 -使用CTE
(又称为WITH子句)为每个用户每天创建一组LINESTRINGS
( MULTILINESTRING
):
WITH j AS (
SELECT userId, creationDateTime, ST_MakeLine(shape) AS shape
FROM locations
GROUP BY userId, creationDateTime)
SELECT userId, ST_AsText(ST_Collect(shape))
FROM j
GROUP BY userId
userid | st_astext
--------------------------------------+----------------------------------------------------------------------------------
d1166a84-ab66-11e8-98d0-529269fb1459 | MULTILINESTRING((-2.22 53.48,-0.11 51.51),(-1.25 51.75,-1.15 52.96,-0.13 50.82))
(1
基本上,您要做的是将所需的记录(在这种情况下为用户和日期)进行分组,并使用您选择的聚合函数,例如ST_MergeLine
, ST_Collect
, ST_Union
, ST_Multi
等。
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