Name
ST_ClosestPointOfApproach — Returns a measure at the closest point of approach of two trajectories.
Synopsis
float8 ST_ClosestPointOfApproach(geometry track1, geometry track2);
Description
Returns the smallest measure at which points interpolated along the given trajectories are the least distance apart.
Inputs must be valid trajectories as checked by ST_IsValidTrajectory. Null is returned if the trajectories do not overlap in their M ranges.
To obtain the actual points at the computed measure use ST_LocateAlong .
Availability: 2.2.0
This function supports 3d and will not drop the z-index.
Examples
Return the time in which two objects moving between 10:00 and 11:00 are closest to each other and their distance at that point.
WITH inp AS ( SELECT
ST_AddMeasure('LINESTRING Z (0 0 0,10 0 5)'::geometry,
extract(epoch from timestamp '2015-05-26 10:00' AT TIME ZONE 'UTC'),
extract(epoch from timestamp '2015-05-26 11:00' AT TIME ZONE 'UTC')
) a,
ST_AddMeasure('LINESTRING Z (0 2 10,12 1 2)'::geometry,
extract(epoch from timestamp '2015-05-26 10:00' AT TIME ZONE 'UTC'),
extract(epoch from timestamp '2015-05-26 11:00' AT TIME ZONE 'UTC')
) b
), cpa AS (
SELECT ST_ClosestPointOfApproach(a, b) m FROM inp
), points AS (
SELECT ST_GeometryN(ST_LocateAlong(a, m), 1) pa,
ST_GeometryN(ST_LocateAlong(b, m), 1) pb
FROM inp, cpa
)
SELECT to_timestamp(m) AT TIME ZONE 'UTC' t,
ST_3DDistance(pa, pb) distance,
pa AS pa, pb AS pb
FROM points, cpa;
-[ RECORD 1 ]----------------------------- t | 2015-05-26 10:45:31.034483 distance | 1.9652147377620688 pa | POINT ZM (7.59 0 3.79 1432637131.03) pb | POINT ZM (9.1 1.24 3.93 1432637131.03)