ST_lcsSubDistance-ApsaraDB RDS(RDS)-阿里云帮助中心

This function computes the distance between a longest common sub-sequence (LCSS) sub-trajectory and a trajectory object.

Syntax

float8 ST_lcsSubDisatance(trajectory traj1, trajectory traj2, float8 dist, distanceUnit unit default 'M');
float8 ST_lcsSubDisatance(trajectory traj1, trajectory traj2, float8 dist, interval lag, distanceUnit unit default 'M');

Parameters

Parameter Name	Description
traj1	The first trajectory object.
traj2	The second trajectory object.
dist	The distance tolerance between two points. The unit is meters (m).
lag	The time tolerance between two points.
unit	The unit of distance. Valid values: 'M': meters. 'KM': kilometers. 'D': degrees. This value is valid only for trajectories that use the WGS84 spatial reference system (spatial reference system identifier (SRID) 4326).

Description

This function computes the sub-trajectory of trajectory object 1 in which trajectory points are consistent with those in the LCSS sub-trajectory, and then returns the ratio between the total number of trajectory points in the sub-trajectory of trajectory object 1 and the number of trajectory points in the LCSS sub-trajectory.

In the figure above, the points [2,3,5] form the LCSS trajectory segment. The corresponding segment in Trajectory 1 is [2,3,4,5], and the result is 1-3/4.

A smaller value indicates a higher similarity between the LCSS sub-trajectory and trajectory object 1.

Generally, a trajectory object has a valid SRID. If not specified, the SRID is 4326 by default.

Examples

With traj AS (
    Select ST_makeTrajectory('STPOINT', 'LINESTRINGZ(114.000528 33.588163 54.87 , 114.000535 33.588235 54.85 , 114.000447 33.588272 54.69 , 114.000348 33.588287 54.73 , 114.000245 33.588305 55.26 , 114.000153 33.588305 55.3)'::geometry,
                             ARRAY['2010-01-01 11:30'::timestamp, '2010-01-01 11:31', '2010-01-01 11:32', '2010-01-01 11:33','2010-01-01 11:34','2010-01-01 11:35'], NULL) a,
           ST_makeTrajectory('STPOINT', 'LINESTRINGZ(114.000529 33.588163 54.87 , 114.000535 33.578235 54.85 , 114.000447 33.578272 54.69 , 114.000348 33.578287 54.73 , 114.000245 33.578305 55.26 , 114.000163 33.588305 55.3)'::geometry,
                             ARRAY['2010-01-01 11:29:58'::timestamp, '2010-01-01 11:31:02', '2010-01-01 11:33', '2010-01-01 11:33:09','2010-01-01 11:34','2010-01-01 11:34:30'], NULL) b)
Select st_LCSSubDistance(a, b, 100) from traj;

st_lcssubdistance 
------------------------
 0.66666666666666666667 
 (1 row)

 With traj AS (
    Select ST_makeTrajectory('STPOINT', 'LINESTRINGZ(114.000528 33.588163 54.87 , 114.000535 33.588235 54.85 , 114.000447 33.588272 54.69 , 114.000348 33.588287 54.73 , 114.000245 33.588305 55.26 , 114.000153 33.588305 55.3)'::geometry,
                             ARRAY['2010-01-01 11:30'::timestamp, '2010-01-01 11:31', '2010-01-01 11:32', '2010-01-01 11:33','2010-01-01 11:34','2010-01-01 11:35'], NULL) a,
           ST_makeTrajectory('STPOINT', 'LINESTRINGZ(114.000529 33.588163 54.87 , 114.000535 33.578235 54.85 , 114.000447 33.578272 54.69 , 114.000348 33.578287 54.73 , 114.000245 33.578305 55.26 , 114.000163 33.588305 55.3)'::geometry,
                             ARRAY['2010-01-01 11:29:58'::timestamp, '2010-01-01 11:31:02', '2010-01-01 11:33', '2010-01-01 11:33:09','2010-01-01 11:34','2010-01-01 11:34:30'], NULL) b)
Select st_LCSSubDistance(a, b, 100, interval '30 seconds') from traj;
st_lcssubdistance 
-------------------
0.666666666666667
(1 row)