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.
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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. |
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Index only kicks in if one of the geometries is a constant e.g. ORDER
BY (ST_GeomFromText('POINT(1 2)') PostGIS geom) instead of g1.geom PostGIS. |
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Availability: 2.2.0 — KNN only available for PostgreSQL 9.1+