[GIS] 3D KNN index in PostGIS

Question

I am looking for a way to do fast KNN queries on a dataset of 10+ million 3D points (and growing). I was hoping PostGIS would do the trick with its new <-> and <#> operators, but they don't seem to work in three dimensions. Does anyone know any workarounds that would extend the KNN GiST index to 3D? Right now I'm using a "normal" spatial index with the &&& operator, but that creates all the issues that led to the addition of the KNN index in the first place.

Answer 1

I know a bit late to reply to this, but PostGIS 2.2 for PostgreSQL 9.5, just recently committed <<->> operator which is a KNN distance for 3D. For 9.5 it returns true 3d distance, for 9.4 and below, just uses 3D bounding box centroid (so would work fine for points).

Details here:

http://postgis.net/docs/manual-dev/geometry_distance_centroid_nd.html

I still need to update the docs, but to utilize the index part, need a 3D index which you create like

CREATE INDEX idx_sometable_geom_nd_gist ON sometable USING gist(geom gist_geometry_ops_nd);