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首頁 云原生數據庫 PolarDB 云原生數據庫PolarDB PostgreSQL版 時空引擎（GanosBase） 常見問題 Trajectory常見問題

Trajectory常見問題

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本文為您介紹Trajectory常見問題和解答，有助于您使用Ganos時空引擎。

如何把坐標點數據轉換為軌跡對象？

采用ST_MakeTrajectory 構造函數可以將其轉換為軌跡對象，設置方法如下：

-- 創建擴展
create extension ganos_trajectory cascade;

-- 創建點表
create table points(id integer, x float8, y float8, t timestamp, speed float8);
insert into points values(1, 128.1, 28.1, '2019-01-01 00:00:00', 100);
insert into points values(2, 128.2, 28.2, '2019-01-01 00:00:01', 101);
insert into points values(3, 128.3, 28.3, '2019-01-01 00:00:02', 102);
insert into points values(4, 128.4, 28.4, '2019-01-01 00:00:04', 103);

-- 創建軌跡表
create table traj(id integer, traj trajectory);

-- 插入數據
insert into traj(id, traj) 
select 1, 
    ST_MakeTrajectory('STPOINT'::leaftype, x, y, 4326, t, ARRAY['speed'], NULL, s, NULL) 
FROM (select array_agg(x order by id) as x,  
      array_agg(y order by id) as y,
      array_agg(t order by id) as t,
      array_agg(speed order by id) as s
  From points) a;

系統自帶的ST_MakTrajectory構造函數不滿足需求怎么辦？

如果系統自帶的ST_MakeTrajectory函數參數不符合應用需求，您可以進行自定義擴展。例如軌跡對象包含2個int8、2個float4和1個timestamp類型的屬性，可以創建如下構造函數：

CREATE OR REPLACE FUNCTION  ST_MakeTrajectory(type leaftype, x float8[], y float8[] , 
               srid integer, timespan timestamp[],attrs_name cstring[], attr1 int8[], 
               attr2 int8[], attr3 float4[], attr4 float4[], attr5 timestamp[])
    RETURNS trajectory
    AS '$libdir/libpg-trajectory16','sqltr_traj_make_all_array'
    LANGUAGE 'c' IMMUTABLE Parallel SAFE;

其中前6個參數為固定類型的參數，后5個參數為用戶自定義的軌跡屬性類型。使用時直接使用用戶定義的重載函數即可。

如何向軌跡中追加軌跡點？

使用ST_append函數向現有軌跡追加軌跡點，ST_append函數聲明如下：

trajectory ST_append(trajectory traj, geometry spatial, timestamp[] timespan, text str_theme_json) ;

trajectory ST_append(trajectory traj, trajectory tail) ;

例如，基于點表向軌跡中追加軌跡點方法如下：

-- 創建擴展
create extension ganos_trajectory cascade;

-- 創建點表
create table points(id integer, x float8, y float8, t timestamp, speed float8);
insert into points values(1, 128.1, 28.1, '2019-01-01 00:00:00', 100);
insert into points values(2, 128.2, 28.2, '2019-01-01 00:00:01', 101);
insert into points values(3, 128.3, 28.3, '2019-01-01 00:00:02', 102);
insert into points values(4, 128.4, 28.4, '2019-01-01 00:00:04', 103);

-- 創建軌跡表
create table traj(id integer, traj trajectory);

-- 插入數據
insert into traj(id, traj) 
select 1, 
    ST_MakeTrajectory('STPOINT'::leaftype, x, y, 4326, t, ARRAY['speed'], NULL, s, NULL) 
FROM (select array_agg(x order by id) as x,  
      array_agg(y order by id) as y,
      array_agg(t order by id) as t,
      array_agg(speed order by id) as s
  From points) a;

-- 插入新軌跡點
insert into points values(5, 128.5, 28.5, '2019-01-01 00:00:05', 105);
insert into points values(6, 128.6, 28.6, '2019-01-01 00:00:06', 106);
insert into points values(7, 128.7, 28.7, '2019-01-01 00:00:07', 107);

-- 基于單點更新軌跡
With point_traj as (
 select ST_MakeTrajectory('STPOINT'::leaftype, x, y, 4326, t, ARRAY['speed'], NULL, s, NULL) AS traj
 FROM (select array_agg(x order by id) as x,  
      array_agg(y order by id) as y,
      array_agg(t order by id) as t,
      array_agg(speed order by id) as s
      From points WHERE ID = 5) a 
)
Update traj 
set traj = ST_append(traj.traj, a.traj)
From point_traj a
WHERE traj.ID=1;

-- 如果使用程序生成SQL也可以寫成
With point_traj as (
 select ST_MakeTrajectory('STPOINT'::leaftype, ARRAY[128.5::float8], 
      ARRAY[28.5::float8], 4326, ARRAY['2019-01-01 00:00:05'::timestamp], 
      ARRAY['speed'], NULL, ARRAY[106::float8], NULL) AS traj
)
Update traj 
set traj = ST_append(traj.traj, a.traj)
From point_traj a
WHERE traj.ID =1;

-- 基于多點更新軌跡
With point_traj as (
 select ST_MakeTrajectory('STPOINT'::leaftype, x, y, 4326, t, ARRAY['speed'], NULL, s, NULL) AS traj
 FROM (select array_agg(x order by id) as x,  
      array_agg(y order by id) as y,
      array_agg(t order by id) as t,
      array_agg(speed order by id) as s
      From points WHERE ID > 5 ) a 
)
Update traj 
set traj = ST_append(traj.traj, a.traj)
From point_traj a
WHERE traj.ID =1;

如何設置字符串類型屬性默認長度？

guc變量ganos.trajectory.attr_string_length用于設置字符串類型屬性。設置方法如下：

Set ganos.trajectory.attr_string_length = 32;

如何計算某個屬性的最大值（最小值/平均值）？

計算某個屬性的最大值（最小值/平均值），方法如下：

With traj AS (
  select '{"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2010-01-01 11:30:00","end_time":"2010-01-01 12:30:00","spatial":"SRID=4326;LINESTRING(1 1,3 5)","timeline":["2010-01-01 11:30:00","2010-01-01 12:30:00"],"attributes":{"leafcount":2,"velocity":{"type":"integer","length":4,"nullable":true,"value":[1,100]},"speed":{"type":"float","length":8,"nullable":true,"value":[null,1.0]},"angel":{"type":"string","length":64,"nullable":true,"value":["test",null]}, "tngel2":{"type":"timestamp","length":8,"nullable":true,"value":["2010-01-01 12:30:00",null]},"bearing":{"type":"bool","length":1,"nullable":true,"value":[null,true]}}}}'::trajectory a)
select avg(v) from 
(
Select unnest(st_trajAttrsAsInteger(a, 'velocity')) as v from traj
) t;