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PostGIS 2.0 Geospatial Software Offers New Features: 3D-4D Indexing

Another feature that has received relatively scant attention in the upcoming release is the ability to index in higher dimensions than the usual two.

Initially I had hoped to made n-dimensional indexing the default, so that multi-dimensional indexes would just automagically be available. Unfortunately it turned out that the overhead involved in having a n-dimensional index key caused the index to be slower.

Rather than slow down the standard use case (2D searching), I re-instated fixed two-dimensional indexing as the default for geometry, and added a new N-D index type for those who want the thrill of extra dimensions.

To build an N-D index, use the following CREATE INDEX statement:

CREATE INDEX my_nd_index 
ON my_table USING GIST (geom gist_geometry_ops_nd);

To query your N-D index, use the &&& operator (note! three ampersands!), like so:

SELECT * FROM my_table 
WHERE geom &&& 'LINESTRING(0 0 0, 2 2 2)';

(“Hey, what’s with the LINESTRING?” Because the index-only query is bounding-volume based, a linestring from the lower-left to the upper-right of my desired bounding volume will have exactly the bounding volume I want.)

Some of the fancy new 3D functions like ST_3DDistance can make use of the 3D index for fast searches in high dimensional spaces. I imagine folks working with XYT data may also find the new indexes useful.

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