Setting up spatial index

I would like to set up a table that contains a 3D position, a time and a measured value, e.g. columns: x, y, z, t, val.

Does bog-standard postgres (i.e. no PostGIS extension, if possible) provide a way to index this table to allow the following 2 types of queries to be performed efficiently?

1. Select all the measurements in a given spatio-temporal box.
2. Select the N points nearest (in the euclidean/pythagorean sense) to a specified point.

If so, how do I define the correct index type, preferably in a manour which is supported by both postgres versions 7.4 and 8.*

I've played with PostGIS a couple of years ago, but, for the sake of installation
simplicity, I'd really prefer to avoid it, and I don't require any of the fancier geometry types, coordinate conversion or GIS functionality. And (back then at least) PostGIS didn't provide any inbuilt 'find nearest' capability (probably because it would be very tricky to implement efficiently if the geometries use ellipsoidal coordinates), although it's easy to do with a no-frills r-tree.

Nathaniel

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