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 '2015-05-26 10:00'::timestamptz),
extract(epoch from '2015-05-26 11:00'::timestamptz)
) a,
ST_AddMeasure('LINESTRING Z (0 2 10, 12 1 2)'::geometry,
extract(epoch from '2015-05-26 10:00'::timestamptz),
extract(epoch from '2015-05-26 11:00'::timestamptz)
) 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) t,
ST_Distance(pa,pb) distance,
ST_AsText(pa, 2) AS pa, ST_AsText(pb, 2) AS pb
FROM points, cpa;
t | distance | pa | pb
-------------------------------+--------------------+--------------------------------------+----------------------------------------
2015-05-26 10:45:31.034483-07 | 1.9603683315139542 | POINT ZM (7.59 0 3.79 1432662331.03) | POINT ZM (9.1 1.24 3.93 1432662331.03)