Control Trajectory Point Density with ST_Resample - PolarDB

Resamples a trajectory by adding or removing points to meet a distance or time threshold.

Syntax

trajectory ST_Resample(trajectory traj, config);

Parameters

Parameter	Description
`traj`	The trajectory to resample.
`config`	A JSON object that specifies the resampling rule. Format: `{"<rule_name>": <value>}`. Only one rule can be specified per call.

Resampling rules

Rule name	Value type	Effect
`add_point.distance_lesser`	Floating-point	Adds intermediate points so that the distance between two consecutive points is smaller than the specified distance.
`add_point.period_lesser`	String (interval)	Adds intermediate points so that the period of time between two consecutive points is smaller than the specified time.
`drop_point.distance_lesser`	Floating-point	Removes intermediate points from consecutive segments whose combined length is less than the specified distance, keeping only the start and end points of the merged segment.
`drop_point.period_lesser`	String (interval)	Removes intermediate points from consecutive segments whose combined duration is less than the specified time, keeping only the start and end points of the merged segment.

Description

ST_Resample resamples a trajectory based on the specified rule and returns an array of sub-trajectories.

Examples

The following examples use a single-point trajectory created with ST_MakeTrajectory.

Add points by distance threshold

Adds points so that the distance between two consecutive points is smaller than 3 units:

SELECT ST_Resample(ST_MakeTrajectory('POINT(1 1)'), '{"add_point.distance_lesser":3}');

Output:

                                                                                        st_resample
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"trajectory":{"version":1,"type":"STPOINT","leafcount":1,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-01 00:00:00","spatial":"POINT(1 1)","timeline":["2000-01-01 00:00:00"]}}
(1 row)

Add points by time threshold

Adds points so that the period of time between two consecutive points is smaller than 2 days:

SELECT ST_Resample(ST_MakeTrajectory('POINT(1 1)'), '{"add_point.period_lesser":"2 day"}');

Output:

                                                                                        st_resample
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"trajectory":{"version":1,"type":"STPOINT","leafcount":1,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-01 00:00:00","spatial":"POINT(1 1)","timeline":["2000-01-01 00:00:00"]}}
(1 row)

Remove points by distance threshold

Removes intermediate points from consecutive segments whose combined length is less than 3 units, keeping only the start and end points:

SELECT ST_Resample(ST_MakeTrajectory('POINT(1 1)'), '{"drop_point.distance_lesser":3}');

Output:

                                                                                        st_resample
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"trajectory":{"version":1,"type":"STPOINT","leafcount":1,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-01 00:00:00","spatial":"POINT(1 1)","timeline":["2000-01-01 00:00:00"]}}
(1 row)