ST_CPAWithin
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## Name

ST_CPAWithin — Tests if the closest point of approach of two trajectories is within the specified distance.

## Synopsis

`boolean ST_CPAWithin(`geometry track1, geometry track2, float8 dist`)`;

## Description

Tests whether two moving objects have ever been closer than the specified distance.

Inputs must be valid trajectories as checked by ST_IsValidTrajectory. False is returned if the trajectories do not overlap in their M ranges.

Availability: 2.2.0

This function supports 3d and will not drop the z-index.

## Examples

    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
    )
    SELECT ST_CPAWithin(a,b,2), ST_DistanceCPA(a,b) distance FROM inp;

     st_cpawithin |     distance
    --------------+------------------
     t            | 1.96521473776207

## See Also

ST_IsValidTrajectory, ST_ClosestPointOfApproach, ST_DistanceCPA, |=|

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