Given two (large) sets of points, how can I efficiently find pairs that are nearest to each other?

Question

I need to solve a computational problem that boils down to searching for reciprocally-nearest pairs of points between two sets. The problem goes something like this:

Giv

Answer 1

• BSP / Octree / Kd-tree (thanks, TZHX)
• Space-filling curves (e.g. using Hilbert curve); google yields many relevant results for pair finding.