## Name

ST_ClosestPointOfApproach — Returns a measure at the closest point of approach of two trajectories.

## Synopsis

`float8 ST_ClosestPointOfApproach(`geometry track1, geometry track2`)`;

## Descrizione

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 .

Disponibilità: 2.2.0

Questa funzione supporta il 3d e non distrugge gli z-index.

## Esempi

```-- 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)
```