What is TPOINT?

TPOINT is a unique software package which analyzes telescope pointing. It has been in use on major telescopes around the World for many years, from the Keck telescopes, ESO VLT, ALMA and GBT downwards. The principle of operation is very simple - you look at stars spread around the sky, recording the telescope readouts on each occasion, and then feed the information into TPOINT. Using powerful but easy to use interactive modelling and graphical commands, you can then identify and measure misalignments and flexures in your telescope. By including in your telescope control system the correction model that TPOINT has found, the various effects are compensated and the pointing errors drastically reduced.

The improvement in pointing performance that TPOINT makes possible is usually spectacular; a telescope which previously required painstaking use of finding charts and manual searching, or time-consuming preliminary acquisition of a nearby bright star, can, after TPOINT modeling, place the images of faint objects directly into the center of the field of view of even a high-power eyepiece.

TPOINT is a must for unattended robotic telescopes. CCD observing becomes a simple matter of commanding the telescope, carrying out the exposure and then, on readout, finding the image of the object under study centered in the frame - every time. In the case of the best observatory instruments, TPOINT helps maintain pointing at the 1-2 arcsecond level, allowing fully automatic acquisition. Amateur instruments routinely achieve 1 arcminute performance, in some cases better than half that figure.

Apart from making target acquisition swift and assured, a less obvious benefit of TPOINT is that with appropriate telescope control software (for example based on the TCSpk or CPK libraries) tracking can be significantly improved. This comes about through the continuous correction of mechanical effects such as cyclic errors in setting circles and encoders, but also as a result of accurate polar alignment. Sites where Polaris is invisible are no problem for TPOINT, which can measure polar axis error to accuracies expressed in arcseconds simply from analyzing pointing in whatever region of the sky happens to be accessible. The TPOINT figures dictate the precise adjustments that need to be made to align the polar axis optimally, important if field rotation is to be minimized.

Two versions of TPOINT are available. One is a Mac or Windows-based system which is fully integrated with the telescope control facilities in the Software Bisque package TheSkyX. The other, the "pro" tool, which uses a traditional command-based user-interface, was until April 2017 licensed by its original author, P.T.Wallace, but is now available from Software Bisque. This latter version (proTPOINT) is the same as that in use at major observatories; it runs under MS-Windows, Linux or Mac OS X. By special arrangement it can also be built for other Unix platforms.

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Copyright © 1998-2018 P.T.Wallace.
Patrick Wallace, 16-Jan-2018