[postgis-users] PostGIS GiST index in 3D

[Bernhard Reimar Hoefle]

Hi!
I'm not a specialist in database indices, therefore the question and some naive
thoughts:

I was looking at lwgeom_gist.c. It uses box1.ymin, box1.ymax, box1.xmax. ... and
so on for the index search.

How much effort would it be to extend the index with the 3rd coordinate? That
means 3D geometry columns would be indexed with their 3D bounding box and if
index searchs are performed with 3D boxes it uses also the z coordinate to
speed-up the query.

I know there is the possibility to search in 2D and then check the z coordinate
(>,<) but I think if you work with for example many 3D points it's quite slow.

To avoid a large overhead with storing the z coordinate for each bounding box in
each index level would it be possible to store for example z only in the higher
levels and not for every feature? That would increase the speed of the index
search in 3D point clouds and avoid a 50% overhead.

I hope to get some answers and more clearance on that topic.

Thanks,
Bernhard