PolarDB:ST_Split

Syntax

trajectory[] ST_Split(trajectory traj, geometry geom, float8 radius_of_buffer);
trajectory[] ST_Split(trajectory traj, text config);
trajectory[] ST_Split(trajectory traj, int[] indexes);

Parameters

Split by geometry

ST_Split(trajectory traj, geometry geom, float8 radius_of_buffer)

Splits the trajectory at any point that falls within the buffer zone around the geometry. Returns the remaining segments as an array of sub-trajectories. When a MultiPoint geometry is provided, the trajectory may be split at multiple locations.

A trajectory point and a geometry object rarely intersect exactly due to floating-point precision. The radius_of_buffer parameter creates a buffer zone around each Point so nearby trajectory points are reliably captured as split locations. Set this value based on your data's coordinate precision and the acceptable spatial tolerance.

Example: Split a trajectory at three points with a 23 km buffer.

CREATE TABLE tr_split_traj (id integer, traj trajectory);

INSERT INTO tr_split_traj VALUES (
  3,
  ST_MakeTrajectory(
    'STPOINT'::leaftype,
    st_geomfromtext('LINESTRING(99.027 29.7555,99.313 29.9975,99.852 30.0745,104.879 35.0795,105.044 35.1235,105.187 35.0685,109.906 35.0795,110.071 35.1675,110.192 35.0355,110.544 35.0245,111.017 34.8045)', 4326),
    ARRAY[
      '2010-01-01 14:30'::timestamp, '2010-01-01 15:00', '2010-01-01 15:10',
      '2010-01-01 15:20', '2010-01-01 15:30', '2010-01-01 15:40',
      '2010-01-01 15:50', '2010-01-01 16:00', '2010-01-01 16:10',
      '2010-01-01 16:20', '2010-01-01 16:30'
    ],
    '{"leafcount":11,"attributes":{"velocity":{"type":"integer","length":2,"nullable":true,"value":[120,130,140,150,160,170,180,190,200,210,220]}}}'
  )
);

SELECT id, unnest(ST_Split(traj, st_geomfromtext('MULTIPOINT(100 30,105 35,110 35)'), 23000)) AS subtraj
FROM tr_split_traj;

The MULTIPOINT geometry splits the trajectory into 4 sub-trajectories, one for each segment between the three split points.

Split by rule

ST_Split(trajectory traj, text config)

Splits the trajectory based on a JSON rule. Pass exactly one rule per call.

The config rules fall into three categories, illustrated below:

• cut_point.* — splits at a sampling point (Point B in the diagram)

• cut_edge.* — splits at an edge between two sampling points (Point C in the diagram)

• drop_edge.* — removes an edge between two sampling points (the edge between Point A and Point B)

WITH traj AS (
  SELECT '{"trajectory":{"version":1,"type":"STPOINT","leafcount":19,...}}'::trajectory AS a
)
SELECT unnest(ST_Split(a, '{"cut_point.max_point":4}')) FROM traj;
-- Returns 5 sub-trajectories: four with 5 points each, one remainder with 3 points.

-- Request 100 parts from a 19-point trajectory (18 edges -> 18 sub-trajectories)
SELECT ST_Split(a, '{"cut_point.even_divide":100}') FROM traj;

-- Split every 50 minutes from the trajectory's start time
SELECT ST_Split(a, '{"cut_edge.time_interval":"50 minute"}') FROM traj;

-- Split at fixed 1-hour boundaries anchored to 2000-01-01 00:00
SELECT unnest(ST_Split(a, '{"cut_edge.time_interval":"1 hour, 2000-01-01"}')) FROM traj;

-- Precision 2: coarse grid, fewer sub-trajectories
SELECT ST_Split(a, '{"cut_edge.geohash":2}') FROM traj;

-- Precision 20: fine grid, more sub-trajectories
SELECT ST_Split(a, '{"cut_edge.geohash":20}') FROM traj;

-- Remove edges longer than 13 units -> returns 1 sub-trajectory (18 remaining points)
SELECT ST_Split(a, '{"drop_edge.spatial_distance_2d":13}') FROM traj;

-- Remove edges longer than 10 units -> returns 7 sub-trajectories
SELECT ST_Split(a, '{"drop_edge.spatial_distance_2d":10}') FROM traj;

-- Remove edges longer than 1 unit -> all edges removed, returns {}
SELECT ST_Split(a, '{"drop_edge.spatial_distance_2d":1}') FROM traj;

Split by index

ST_Split(trajectory traj, int[] indexes)

Splits the trajectory at the specified point indexes. Indexes start from 0. Given n indexes, the function produces n-1 sub-trajectories. The start and end points of the trajectory do not need to be included in the index array.

Example: Split at indexes 1, 3, and 5 — returns 2 sub-trajectories (segments [1–3] and [3–5]).

WITH traj AS (
  SELECT '{"trajectory":{"version":1,"type":"STPOINT","leafcount":19,...}}'::trajectory AS a
)
SELECT unnest(ST_Split(a, '{1,3,5}'::int[])) FROM traj;
-- Returns 2 sub-trajectories.

Example: Including the start (0) and end (ST_leafcount(a) - 1) indexes in the array has no effect on split behavior, but makes the index boundaries explicit.

SELECT unnest(ST_Split(a, '{0}'::int[] || '{0,1,3,5}'::int[] || ST_leafcount(a) - 1)) FROM traj;
-- Returns 4 sub-trajectories (duplicate index 0 is ignored).

What's next

• ST_MakeTrajectory — construct a trajectory from geometry and timestamps

• ST_leafcount — get the number of sampling points in a trajectory