Closest Pair Queries with Spatial Constraints

Given two datasets DA and DB the closest-pair query (CPQ) retrieves the pair (a,b), where a ∈ DA and b ∈ DB, having the smallest distance between all pairs of objects. An extension to this problem is to generate the k closest pairs of objects (k-CPQ). In several cases spatial constraints are applied, and object pairs that are retrieved must also satisfy these constraints. Although the application of spatial constraints seems natural towards a more focused search, only recently they have been studied for the CPQ problem with the restriction that DA = DB. In this work we focus on constrained closest-pair queries (CCPQ), between two distinct datasets DA and DB, where objects from DA must be enclosed by a spatial region R. A new algorithm is proposed, which is compared with a modified closest-pair algorithm. The experimental results demonstrate that the proposed approach is superior with respect to CPU and I/O costs.