HATS Pointing Model

The Sky X pointing model interface

Introduction

The Pointing Model is a function that corrects the telescope pointing. The function is composed of several terms each one has two factors: a function of the telescope coordinates that can be a trigonometric or polynomial; and a parameter that multiplies the function. The final correction value is obtained by adding all the different terms.

$\Delta x_i = \sum f_i(x_1,x_2) \times A_i$

where $(x_1,x_2)$ are the telescope coordinates (they can be azimuth and elevation, or right ascension and declination), $f_i()$ are the different functions, and $A_i$ are the multiplication factors (parameters). Examples of functions $f_i(x_1,x_2)$ are

$\Delta h = -MA \cos(h) \tan(\delta) \quad , \quad \Delta \delta = +MA \sin (h)$

$\Delta \delta = + ID$

with $h$ the hour angle and $\delta$ the declination. $\Delta h$ is the correction for the hour angle; $\Delta\delta$ is the correction for the declination.

HATS currently uses 7 functions in the Pointing Model which was developed by Patrick Wallace, the expert developer and owner of the TPoint software. It is important to note that when we talk about a "model", we may refer to two different things:

1. The set of functions to use. HATS model uses 7 functions described in the TPoint manual.
2. The value of each parameter.

The following table shows the parameter names and their values as of 2025-04-13:

  Name     Value
  ID       -815
  ME      -9106
  MA      +8852
  HHSH     -922
  HHCH    -2577
  HDSH    -7163
  HDCH    +8714

Pointing Corrections and Measurements

(Needs to be written)

Model Determination

Every pointing correction is stored in the file /home/observer/Library/Application Support/Software Bisque/TheSkyX Professional Edition/TPoint/TPoint base run in.dat in.dat