Two-particle correlations have been measured for identified π- from central 158 A GeV Pb+Pb collisions and fitted radii of about 7 fm in all dimensions have been obtained. A multi-dimensional study of the radii as a function of kT is presented, including a full correction for the resolution effects of the apparatus. The cross term R2out-long of the standard fit in the Longitudinally CoMoving System (LCMS) and the vL parameter of the generalised Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a boost invariant expansion. The shapes of the correlation functions in Qinv and Qspace = √Q2x + Q2y + Q2z have been analyzed in detail. They are not Gaussian but better represented by exponentials. As a consequence fitting Gaussians to these correlation functions may produce different radii depending on the acceptance of the experimental setup used for the measurement.