ST_AccompanyIntervals函數用於計算兩條軌跡的伴隨運動區間-雲原生資料庫 PolarDB-阿里雲

計算兩條軌跡伴隨運動的區間。

文法

Table(timestamp start_time, timestamp end_time) ST_AccompanyIntervals(trajectory traj1, trajectory traj2, double precision tol_dist, interval merge_gap default '0 minute', interval min_length default '0 minute', character(1) dist_config defaut 'A');

Table(trajectory traj1, trajectory subtraj2) ST_AccompanyParts(trajectory traj1, trajectory traj2, double precision tol_dist, interval merge_gap default '0 minute', interval min_length default '0 minute', character(1) dist_config defaut 'A');

參數

參數名稱	描述
traj1	軌跡對象1。
traj2	軌跡對象2。
tol_dist	伴隨距離，小於此距離時認為兩條軌跡伴隨運動。使用對應SRID下預設的距離單位。說明通常情況下，當SRID=4326時，使用米為單位。
merge_gap	ST_AccompanyIntervals：如果兩個時間段之間距離小於merge_gap，則將兩個時間段合并。若不指定，不進行合并。 ST_AccompanyParts：當兩組伴隨子軌跡之間的距離小於merge_gap時，將兩組子軌跡合并。若不指定，不進行合并。
min_length	當一個伴隨時間段的時間長度小於min_length時，將其捨棄。若不指定，不進行捨棄。
dist_config	距離計算的方式，取值範圍如下： `'W'`，表示將橫縱座標解讀為按照WGS84座標系下的座標點來計算距離。 `'C'`，表示直接對橫縱座標計算距離。 `'M'`，表示以米為單位進行計算，等價於'W'。 `'D'`，表示以角度為單位進行計算，等價於'C'。 `'A'`或不指定時，表示自動選擇（SRID為4326時使用`'W'`，其它使用`'C'`）。

傳回值

返回列名稱	描述
start_time	伴隨時間開始。
end_time	伴隨時間結束。
traj1	軌跡對象1上的子軌跡。
traj2	軌跡對象2上的子軌跡。

描述

同一時刻的提取軌跡上，兩條軌跡之間距離小於tol_dist的軌跡時間段。
在ST_AccompanyIntervals中如果兩個時間段之間距離小於merge_gap，則將兩個時間段合并。執行完合并步驟之後，如果有一個伴隨時間段長度依然小於min_length，將其捨棄。
在ST_AccompanyParts中如果兩個子軌跡之間距離小於merge_gap，則將兩個子軌跡合并。執行完合并步驟之後，如果有一個伴隨時間段長度依然小於min_length，將其捨棄。
ST_AccompanyIntervals返回對應的時間段，而ST_AccompanyParts則返回這些時間段上traj1和traj2的子軌跡。

樣本

ST_AccompanyIntervals

With traj AS
(
SELECT ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 1 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as a, ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 0 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as b
)
SELECT (ST_AccompanyIntervals(a,b,0.5)).* from traj;

返回結果如下：

     start_time      |      end_time       
---------------------+---------------------
 2000-01-01 00:00:00 | 2000-01-01 12:00:00
 2000-01-02 12:00:00 | 2000-01-03 00:00:00
(2 rows)

區間合并

With traj AS
(
SELECT ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 1 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as a, ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 0 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as b
)
SELECT (ST_AccompanyIntervals(a,b,0.5,'2 day')).* from traj;

返回結果如下：

     start_time      |      end_time       
---------------------+---------------------
 2000-01-01 00:00:00 | 2000-01-03 00:00:00
(1 row)

ST_AccompanyParts

With traj AS
(
SELECT ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 1 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as a, ST_MakeTrajectory('STPOINT','LINESTRING(0 0, 0 0, 0 0)'::geometry, '2000-01-01'::timestamp, '2000-01-03', NULL) as b
)
SELECT (ST_AccompanyParts(a,b,0.5)).* from traj;

返回結果如下：

                                                                                                            traj1                                                                                                            |             
                                                                                             traj2                                                                                                           
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-01 12:00:00","spatial":"LINESTRING(0 0,0.5 0)","timeline":["2000-01-01 00:00:00","2000-01-01 12:00:00"]}} | {"trajectory
":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-01 12:00:00","spatial":"LINESTRING(0 0,0 0)","timeline":["2000-01-01 00:00:00","2000-01-01 12:00:00"]}}
 {"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-02 12:00:00","end_time":"2000-01-03 00:00:00","spatial":"LINESTRING(0.5 0,0 0)","timeline":["2000-01-02 12:00:00","2000-01-03 00:00:00"]}} | {"trajectory
":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-02 12:00:00","end_time":"2000-01-03 00:00:00","spatial":"LINESTRING(0 0,0 0)","timeline":["2000-01-02 12:00:00","2000-01-03 00:00:00"]}}
(2 rows)