|=|
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## Name

|=| — Returns the distance between A and B trajectories at their closest point of approach.

## Synopsis

`double precision |=|(` geometry A , geometry B `)`;

## Description

The `|=|` operator returns the 3D distance between two trajectories (See ST_IsValidTrajectory). This is the same as ST_DistanceCPA but as an operator it can be used for doing nearest neighbor searches using an N-dimensional index (requires PostgreSQL 9.5.0 or higher).

This operand will make use of ND GiST indexes that may be available on the geometries. It is different from other operators that use spatial indexes in that the spatial index is only used when the operator is in the ORDER BY clause.

Index only kicks in if one of the geometries is a constant (not in a subquery/cte). e.g. 'SRID=3005;LINESTRINGM(0 0 0,0 0 1)'::geometry instead of a.geom

Availability: 2.2.0. Index-supported only available for PostgreSQL 9.5+

## Examples

    -- Save a literal query trajectory in a psql variable...
    \set qt 'ST_AddMeasure(ST_MakeLine(ST_MakePointM(-350,300,0),ST_MakePointM(-410,490,0)),10,20)'
    -- Run the query !
    SELECT track_id, dist FROM (
      SELECT track_id, ST_DistanceCPA(tr,:qt) dist
      FROM trajectories
      ORDER BY tr |=| :qt
      LIMIT 5
    ) foo;
     track_id        dist
    ----------+-------------------
          395 | 0.576496831518066
          380 |  5.06797130410151
          390 |  7.72262293958322
          385 |   9.8004461358071
          405 |  10.9534397988433
    (5 rows)

## See Also

ST_DistanceCPA, ST_ClosestPointOfApproach, ST_IsValidTrajectory

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