  The imager on board INTEGRAL (IBIS) presently provides the most detailed sky
images ever obtained at energies above 30 keV. The telescope is based on a
coded aperture imaging system which allows to obtain sky images in a large
field of view 29deg x 29deg with an angular resolution of 12'. The System Point
Spread Function of the telescope and its detailed characteristics are here
described along with the specific analysis algorithms used to derive the
accurate point-like source locations. The derived location accuracy is studied
using the first in-flight calibration data on strong sources for the IBIS/ISGRI
system. The dependence of the calibrated location accuracy with the signal to
noise ratio of the sources is presented. These preliminary studies demonstrate
that the IBIS/ISGRI telescope and the standard scientific analysis software
allow source localizations with accuracy at 90% confidence level better than 1'
for sources with signal to noise ratios > 30 over the whole field of view, in
agreement with the expected performances of the instrument.
