TPoint

TPOINT is a software package used in astronomy to analyze and model telescope pointing errors and to derive pointing corrections. The program helps observatories and amateur astronomers improve the accuracy with which a telescope aims at a given sky position by creating a mathematical model of pointing error as a function of variables such as telescope orientation, mechanical flexure, and atmospheric refraction.

Using a pointing run, the user points at a set of well-known stars across the sky and records the measured image coordinates (or offsets) and the corresponding telescope encoder readings. These data are fit to a parameterized model comprising terms that represent common error sources (e.g., axis misalignment, non-perpendicularity of axes, encoder zero-point errors, flexure, and refraction). The software estimates the model parameters, often iteratively, to minimize residuals between observed and predicted positions.

Once the model is determined, the resulting pointing corrections can be applied to future observations, either by updating the mount's pointing model file or through real-time corrections in the control system. Features include diagnostics and visualization tools to examine residuals, model term significance, and data quality; support for different mount types; and generation of reports and model files.

TPOINT has become widely used in professional and amateur contexts and is considered a standard approach to telescope pointing calibration. Its methodology has influenced the development of subsequent pointing calibration tools and workflows.