In view of the recent postings about TPOINT it might help if I listed a
few FAQs. See the Tpoint Software web pages for more information.

* What are TPOINT and SLALIB?

TPOINT is a computer package that analyses telescope pointing
observations and tells you about the misalignments, flexures,
runouts and so on in your telescope.

SLALIB is a library of (mainly) positional-astronomy routines.
TPOINT does all its precession etc by calling SLALIB routines.
(SLALIB covers much the same ground as Jan Meeus's "Astronomical
Algorithms". The latter is a better starting point for hobbyist
programmers.)

* Are TPOINT and SLALIB academic or proprietary software?

There is a Fortran-based version of SLALIB supported (mainly for
professional use) by the UK Starlink Project. Libraries for various
Unix platforms are available. There used to be a Fortran-based version
of TPOINT as well, developments of algorithms originally developed for
the AAT project in the 1970s. This is no longer supported. There are
also proprietary versions of SLALIB and TPOINT, both written in C, and
marketed by Tpoint Software under arrangements agreed some years ago
with CCLRC/RAL.

Although astronomy research institutes use SLALIB for free (not TPOINT
though), note that this concession does not extend to for-profit use.
Potential users should refer to the copyright and disclaimer notices.

* How do you use TPOINT?

Whenever you want to check out your pointing, you observe maybe 30
stars all over the sky and feed the data into TPOINT. The package has
rich model-building, fitting and graphical display tools that allow
various deficiencies to be exposed and measured. The numbers can be
fed into your telescope control system to improve the pointing and
tracking. Or you can use the information to tell you what needs
adjusting mechanically, for example the polar axis.

Once you've got a good model for your telescope, you can use it as
the basis for a brief start-of-night recalibration, correcting just
the zero-points, plus collimation errors perhaps, and polar axis
misalignment if the telescope is non-permanent. This may only take
two or three stars at a pinch.

Repeated pointing tests over time will monitor changes in your
telescope and give early warning of mechanical problems. You will
also build up a large data set from which additional pointing terms
can be gleaned.

* How does TPOINT work?

TPOINT reads files of pointing data and does all the necessary
positional-astronomy transformations to predict where in the sky the
star should have been seen. The raw telescope readings will not, in
general, agree with these positions; models describing how the
disagreement varies around the sky are constructed interactively from
a repertoire of likely terms. SVD-based least-squares fitting
techniques estimate the coefficient values for the model, and tell
you whether a given term is statistically significant. Through a
number of graphical tools, remaining uncorrected errors can be viewed.

* How well does TPOINT work?

TPOINT squeezes out of any given telescope all the available pointing
performance: some large telescopes deliver pointing at the 1 arcsecond
level using TPOINT models. An LX-200 should achieve about 1 arcminute RMS,
all-sky, and drop sources straight into the center of a CCD. You should
also be able to measure polar alignment on an LX-200 to better than
30 arcsec using TPOINT.

* What's the difference between the two TPOINTs?

The Software Bisque version and the Tpoint Software version both use
not just the same algorithms but in fact the same core of C code. The
differences are principally to do with the user interface. The SB
version is integrated with TheSky and has a windows interface. The
native, or "pro", version is command-line driven.


Patrick Wallace

---------------------------------------------------------------------
TPOINT SOFTWARE http://www.tpsoft.demon.co.uk/
_____________________________________________________________________

View index by [date] [author] [subject]
Previous message: Re: [M]: 416/6.4 Success!, Chris Heapy
Next message: [M]: Re: The Sky Communication Problem, Larry Wood
Next message in thread: Re: [M]: Tpoint and LX200, Bill Arnett
Previous message in thread: Re: [M]: Tpoint and LX200, Bob Elliott