  The Gemini Planet Imager (GPI) combines extreme adaptive optics, an integral
field spectrograph, and a high performance coronagraph to directly image
extrasolar planets in the near-infrared. Because the coronagraph blocks most of
the light from the star, it prevents the properties of the host star from being
measured directly. Instead, satellite spots, which are created by diffraction
from a square grid in the pupil plane, can be used to locate the star and
extract its spectrum. We describe the techniques implemented into the GPI Data
Reduction Pipeline to measure the properties of the satellite spots and discuss
the precision of the reconstructed astrometry and spectrophotometry of the
occulted star. We find the astrometric precision of the satellite spots in an
$H$-band datacube to be $0.05$ pixels and is best when individual satellite
spots have a signal to noise ratio (SNR) of $> 20$. In regards to satellite
spot spectrophotometry, we find that the total flux from the satellite spots is
stable to $\sim 7\%$ and scales linearly with central star brightness and that
the shape of the satellite spot spectrum varies on the $2\%$ level.
