轨迹表

以某出行APP的数据为例，其建表语句为：

CREATE TABLE trajectory_table(
    userid numeric PRIMARY KEY, 
    traj trajectory
);

创建轨迹支持多种方式，具体如下：

• 将点表转化为轨迹，具体请参见点表。

  由于执行GROUP BY操作时不一定保证点的次序，因此需要调用ST_Sort()函数，将轨迹点根据时间重新排序。

  INSERT INTO trajectory_table
  SELECT userid, ST_Sort(ST_MakeTrajectory(pnts.tjraw, true, '{"intensity"}'::cstring[]))
  FROM
  (SELECT sample_points.userid, 
          array_agg(
              ROW(sample_points.sample_time, 
                  sample_points.x, 
                  sample_points.y, 
                  sample_points.z, 
                  sample_points.intensity)) 
          AS tjraw FROM sample_points GROUP BY userid
  ) pnts;

• ST_makeTrajectory提供多种方式构造轨迹：

  说明

  本示例仅展示ID为1的轨迹，通过Geometry类型+时间戳数组+属性JSON串构造轨迹。

  INSERT INTO trajectory_table 
  SELECT 3, ST_MakeTrajectory(
              'STPOINT'::leaftype, 
              st_geomfromtext('LINESTRING(114.35 39.28 4,114.36 39.28 4,114.35 39.29 4)', 4326), 
              ARRAY['2020-04-11 17:42:30'::timestamp,'2020-04-11 17:43:30'::timestamp,'2020-04-11 17:45:00'::timestamp], 
              '{"leafcount":3,"attributes":{"intensity":{"type":"integer","length":4,"nullable":true,"value":[80,30,50]}}}'
  );           

  说明

  ST_makeTrajectory函数提供多种方式构造轨迹，一些方式需要依赖Ganos的Geometry几何类型，更多信息，请参见几何类型。

• JSON字符串构建轨迹：

  INSERT INTO trajectory_table
  SELECT 4, 
  '{"trajectory":{"version":1,"type":"STPOINT","leafcount":3,"start_time":"2020-04-11 17:42:30","end_time":"2020-04-11 17:45:00","spatial":"SRID=4326;LINESTRING(114.35 39.28 4,114.36 39.28 4,114.35 39.29 4)","timeline":["2020-04-11 17:42:30","2020-04-11 17:43:30","2020-04-11 17:45:00"],"attributes":{"leafcount":3,"intensity":{"type":"integer","length":4,"nullable":true,"value":[80,30,50]}}}}'
  ::trajectory;

对于整条的轨迹，支持进行时空相关的操作，例如相交、包含的判断等。通过建立R树索引，可以加速空间查询。

--创建索引。
CREATE INDEX ON trajectory_table USING gist(traj);

--查找所有与一个二维矩形范围相交的轨迹，返回其userid。
SELECT userid FROM trajectory_table WHERE ST_2DIntersects(traj, ST_MakeEnvelope(114.33,39.28,14.331,39.282));