<#>
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## Name

<#> — Returns the 2D distance between A and B bounding boxes.

## Synopsis

`double precision <#>(` geometry A , geometry B `)`;

## Description

The `<#>` operator returns distance between two floating point bounding boxes, possibly reading them from a spatial index (PostgreSQL 9.1+ required). Useful for doing nearest neighbor approximate distance ordering.

This operand will make use of any 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 e.g. ORDER BY (ST_GeomFromText('POINT(1 2)') <#> geom) instead of g1.geom <#>.

Availability: 2.0.0 -- KNN only available for PostgreSQL 9.1+

## Examples

    SELECT *
    FROM (
    SELECT b.tlid, b.mtfcc,
    	b.geom <#> ST_GeomFromText('LINESTRING(746149 2948672,745954 2948576,
    		745787 2948499,745740 2948468,745712 2948438,
    		745690 2948384,745677 2948319)',2249) As b_dist,
    		ST_Distance(b.geom, ST_GeomFromText('LINESTRING(746149 2948672,745954 2948576,
    		745787 2948499,745740 2948468,745712 2948438,
    		745690 2948384,745677 2948319)',2249)) As act_dist
        FROM bos_roads As b
        ORDER BY b_dist, b.tlid
        LIMIT 100) As foo
        ORDER BY act_dist, tlid LIMIT 10;

       tlid    | mtfcc |      b_dist      |     act_dist
    -----------+-------+------------------+------------------
      85732027 | S1400 |                0 |                0
      85732029 | S1400 |                0 |                0
      85732031 | S1400 |                0 |                0
      85734335 | S1400 |                0 |                0
      85736037 | S1400 |                0 |                0
     624683742 | S1400 |                0 | 128.528874268666
      85719343 | S1400 | 260.839270432962 | 260.839270432962
      85741826 | S1400 | 164.759294123275 | 260.839270432962
      85732032 | S1400 |           277.75 | 311.830282365264
      85735592 | S1400 |           222.25 | 311.830282365264
    (10 rows)

## See Also

ST_DWithin, ST_Distance, <->

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