PostGIS 2.0 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.