  GRETA, the Gamma-Ray Energy Tracking Array, is an array of highly-segmented
HPGe detectors designed to track {\gamma}-rays emitted in beam-physics
experiments. Its high detection efficiency and state-of-the-art position
resolution make it well-suited for imaging applications. In this paper, we
derive the expressions for locating a photon emission point using Compton
imaging. We also include expressions for corresponding uncertainty
calculations.
