  We show that the pointer basis distinguished by collisional decoherence
consists of exponentially localized, solitonic wave packets. Based on the
orthogonal unraveling of the quantum master equation, we characterize their
formation and dynamics, and we demonstrate that the statistical weights arising
from an initial superposition state are given by the required projection. Since
the spatial width of the pointer states can be obtained by accounting for the
gas environment in a microscopically realistic fashion, one may thus calculate
the coherence length of a strongly interacting gas.
