Automatic Registration

This makes an inventory of the sources above a threshold in each frame. It then performs a pattern recognition to identify common features in jittered frames. If the fraction of common objects is under 40% or the total is fewer than three, the registration fails, and so the script resorts to reading the telescope offsets stored in the FITS headers, or matching a central bright object in certain recipes. Using telescope offsets can lead to trailed sources, as occurred with the IRCAMDR package. The improved registration leads to the detection of fainter sources and more-accurate measurement thereof.
[_GENERATE_OFFSETS_ invoked within several wrappers tied to various families of recipes, _FIND_APPROX_OFFSETS_, _TELE_OFFSETS_, _GENERATE_TELE_OFFSETS_,
_GET_CARTESIAN_TELESCOPE_OFFSETS_]

To make use of the best information, registration using more than one of the above methods is permitted.

There is also a new but not extensively tested option in which matching is performed only within overlapping regions as specified from the approximate world co-ordinate system, and a single match within 12 pixels is allowed to define the offsets between frames. This modification should allow more registrations using sources than from telescope offsets, which merely assist in the process. Since the robustness is unknown at present, this option is currently disabled by default. The easiest way to switch it on, is to change the the default value of the SKYREG argument primitive _GENERATE_OFFSETS_ to 1. See the notes on customising recipes for generic instructions to make a private _GENERATE_OFFSETS_.

NACO has a tiny plate scale; even with adaptive optics the tolerances (minimum number of pixels and the percentile threshold) searching for fiducial sources are increased, and by default the sky registration is enabled.
[NACO/_GENERATE_OFFSETS_]