Abstract
We present a theoretical analysis of the Diffracto-Astrometry measuring algorithm. We generated Tiny-Tim Theoretical Point Spread Functions (PSFs) for the CCDs in the HST Wide Field Planetary Camera 2 (WFPC2). These images were then measured using only their diffraction pattern, and positions for the simulated PSFs were obtained. The measuring algorithm recovers the original positions reasonably well (±0.1 to ±0.4 pixels). However, slight deviations from the original values are observed. We adjust the differences between the real and the measured position with a quadratic function of the coordinates. Application of these transformations allows determination of the position of a stellar image within a few hundredths of a pixel.
