自定义轨迹编辑函数

某用户的每个设备上有三个传感器，分别为1，2，3，传感器汇报位置时会附加一个可信度属性。则可以自定义轨迹编辑函数，实现如下功能：

• 从一条轨迹中过滤出所有可信度大于某值的点，返回其组成的轨迹。

  CREATE FUNCTION UDF_validityGreaterThan(traj trajectory, threshold float8)
  RETURNS trajectory
  AS
  '
  SELECT ST_MakeTrajectory(array_agg(ROW(traj_table.*))) FROM
  (
    SELECT * from ST_AsTable(traj) as f(t timestamp, x double precision, y double precision, sampler int, validity double precision)
  ) traj_table
  WHERE validity > threshold
  '
  LANGUAGE SQL IMMUTABLE STRICT PARALLEL SAFE;

• 从一条轨迹中过滤出特定传感器汇报的所有点，返回其组成的轨迹。

  CREATE FUNCTION UDF_SamplerIs(traj trajectory, int sampler_num)
  RETURNS trajectory
  AS
  '
  SELECT ST_MakeTrajectory(array_agg(ROW(traj_table.*))) FROM
  (
    SELECT * from ST_AsTable(traj) as f(t timestamp, x double precision, y double precision, sampler int, validity double precision)
  ) traj_table
  WHERE sampler = sampler_num
  '
  LANGUAGE SQL IMMUTABLE STRICT PARALLEL SAFE;