Name
<#> — Returns the distance between bounding box of 2 geometries. For point / point checks it's almost the same as distance (though may be different since the bounding box is at floating point accuracy and geometries are double precision). Useful for doing distance ordering and nearest neighbor limits using KNN gist functionality.
Synopsis
double precision <#>(
geometry
A
,
geometry
B
);
Description
The <#> KNN GIST operator returns distance between two floating point bounding boxes read from the spatial index if available. Useful for doing nearest neighbor approximate distance ordering.
![[Note]](images/note.png) | |
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 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)