donuts 0.4.0
Align astronomical images
License: MIT

=======
Donuts
=======

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A science frame autoguiding and image alignment algorithm with sub-pixel
precision, capable of guiding on defocused stars.


Project documentation: https://donuts.readthedocs.io/en/latest/

See the changelog_ for latest changes.

Motivation
----------

We operate or have access to several telescopes (NGTS, NITES, Warwick
1m, 1.5m San Pedro Martir) that require precise autoguiding. Sometimes
we need to defocus a telescope but we would still like to autoguide. 
Donuts was designed to allow this. The algorithm had to be
simple, fast and accurate. It has been shown to perform well as an 
autoguiding algorithm for equatorial telescopes (no field rotation).

The process of aligning apertures for photometry is essentially the same. 
Rather than correcting the telescope pointing, the apertures
must track the drift of the stars. Donuts can therefore be used to track
the stellar positions for CCD photometry also.

By default Donuts measures frame-to-frame translational offsets (X
and Y) using all the stars in the image. The algorithm could be adjusted 
in the to select a specific region of interest (for extremely wide or
distorted fields).

The algorithm has its limitations. It currently does not deal with
rotation or very large drifts - where the field moves by approx. half a FOV
or more. Our paper describing the details can be found here:

http://adsabs.harvard.edu/abs/2013PASP..125..548M

Example
-------

Below is a sample of 10 nights autoguiding residuals from NGTS while using 
Donuts. The upper plot shows the frame-to-frame error, while the bottom 
shows the drift which would have occured if not for Donuts. Aligning 
photometry apertures is essentially the same process and similar performance
is expected under that scenario. We routinely achieve an autoguiding RMS of 
1/20 pixels with NGTS. 

.. image:: AgResiduals_802_March2016.png

Contributors
------------

`James McCormac <https://github.com/jmccormac01>`_,
`Simon Walker <https://github.com/mindriot101>`_.


License
-------

MIT License

Copyright (c) 2021 James McCormac & Simon Walker

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

.. _changelog: https://github.com/jmccormac01/Donuts/blob/devel/CHANGELOG.md