  Ultraviolet Imaging Telescope (UVIT) is one of the payloads onboard AstroSat,
India's first multi-wavelength Astronomy mission. UVIT is primarily designed to
make high resolution images in wide field, in three wavelength channels
simultaneously: FUV (130 - 180 nm), NUV (200 - 300 nm) and VIS (320 - 550 nm).
The intensified imagers used in UVIT suffer from distortions, and a correction
is necessary for these to achieve good astrometry. In this article we describe
the methodology and calculations used to estimate the distortions in ground
calibrations.
