This topic describes the ST_Resample function. This function resamples a trajectory.
Syntax
trajectory ST_Resample(trajectory traj, config);Parameters
Parameter | Description |
traj | The trajectory that is resampled. |
config | The rule that is used to resample the trajectory. Format: |
Only one rule can be specified by the config parameter. The following table describes the rules that you can specify by using the config parameter.
Rule | Type | Description |
add_point.distance_lesser | Floating point | Evenly add points to each trajectory so that the distance between two points is smaller than the parameter value. |
add_point.period_lesser | String that can be converted into the INTERVAL type | Evenly add points to each trajectory so that the period of time between two points is smaller than the parameter value. |
drop_point.distance_lesser | Floating point | When the distance between all points of consecutive segments of a trajectory and the start point of the trajectory is less than the value of this rule, the consecutive segments are merged. Only the start and end points of the obtained segment are retained. |
drop_point.period_lesser | String that can be converted into the INTERVAL type | When the sum of time of periods required between multiple consecutive segments of a trajectory is less than the given period of time, merge the consecutive segments. Only the start and end points of the obtained segment are retained. |
Description
This function resamples a trajectory based on the specified rule and returns the resampling result.
Examples
With traj As
(
select '{"trajectory":{"version":1,"type":"STPOINT","leafcount":5,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,10 10,11 11,13 13,15 15)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}'::trajectory a
)
SELECT ST_Resample(a, '{"add_point.distance_lesser":3}') from traj;
st_resample
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
{"trajectory":{"version":1,"type":"STPOINT","leafcount":9,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,2.8 2.8,4.6 4.6,6.4 6.4,8.2 8.2,10 10,11 11,13 13,15 15)","timeline":["2000-01-01 00:00:00","2000-01-01 04:48:00","2000-01-01 09:36:00","2000-01-01 14:24:00","2000-01-01 19:12:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}
(1 row)
With traj As
(
select '{"trajectory":{"version":1,"type":"STPOINT","leafcount":5,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,10 10,11 11,13 13,15 15)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}'::trajectory a
)
SELECT ST_Resample(a, '{"add_point.period_lesser":"0.5 day"}') from traj;
st_resample
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
{"trajectory":{"version":1,"type":"STPOINT","leafcount":9,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,5.5 5.5,10 10,10.5 10.5,11 11,12 12,13 13,14 14,15 15)","timeline":["2000-01-01 00:00:00","2000-01-01 12:00:00","2000-01-02 00:00:00","2000-01-02 12:00:00","2000-01-03 00:00:00","2000-01-03 12:00:00","2000-01-04 00:00:00","2000-01-04 12:00:00","2000-01-05 00:00:00"]}}
(1 row)
With traj As
(
select '{"trajectory":{"version":1,"type":"STPOINT","leafcount":5,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,10 10,11 11,13 13,15 15)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}'::trajectory a
)
SELECT ST_Resample(a, '{"drop_point.distance_lesser":3}') from traj;
st_resample
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
{"trajectory":{"version":1,"type":"STPOINT","leafcount":4,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(1 1,10 10,13 13,15 15)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}
(1 row)