This paper has presented a new solution to the simultaneous
localization and mapping (SLAM) problem with six degrees of
freedom. The method is based on the ICP scan matching
algorithm. The paper investigates approximate data association
using 
d-trees and bd-trees. d-trees empirically outperfom
bd-trees with and without approximation. Approximation does not
significantly deteriorate the quality of scan registration. From
that we know of no other superior approach, scan matching based
on reduced point sets and approximate d-trees is currently the
most performant method at hand for scan matching in 6D SLAM.