Fig. 2

The sketch of a possible error such that the proposed scheme misses the data point X, which is among the \(k\)-NN of a queried data point Q. When X occurs in a different volume \(v_j\) than the volume \(v_i\) of the query Q, it can not be considered as a candidate \(k\)-NN of Q as X and Q will then reside in different leaves of the created B+ tree.