function align_frame(img_to, img_from;
    [box_size],
    [ap_radius],
    [f],
    [min_fwhm],
    [nsigma],
)

Align img_from onto img_to. See below for keyword arguments currently available to control this process.

• box_size: The size of the grid cells (in pixels) used to extract candidate point sources to use for alignment. Defaults to a tenth of the greatest common denominator of the dimensions of img_to. See Photometry.jl > Source Detection Algorithms for more.
• ap_radius: The radius of the apertures (in pixel) to place around each point source. Defaults to 60% of first(box_size). See Photometry.jl > Aperture Photometry for more.
• f: The function to compute within each aperture. Defaults to a 2D Gaussian fitted to the aperture center. See the Source characterization section of the accompanying Pluto.jl notebook for more.
• min_fwhm: The minimum FWHM (in pixels) that an extracted point source must have to be considered as a control point. Defaults to a fifth of the width of the first image. See PSFModels.jl > Fitting data for more.
• nsigma: The number of standard deviations above the estimated background that a source must be to be considered as a control point. Defaults to 1. See Photometry.jl > Source Detection Algorithms for more.

get_sources(img; box_size = nothing, nsigma = 1)

Extract candidate sources in img according to Photometry.Detection.extract_sources. By default, img is first sigma clipped and then background subtracted before the candidate sources are extracted. box_size is passed to Photometry.Background.estimate_background, and nsigma is passed to Photometry.Detection.extract_sources. See the Photometry.jl documentation for more.

TODO: Pass more options to clipping, background estimating, and extraction methods in Photometry.jl.

find_nearest(C_to, ℳ_to, C_from, ℳ_from)

Return the closes pair of three points between the from and to frames in the invariant $\mathscr M$ space as computed by Astroalign.triangle_invariants.

triangle_invariants(phot)

Returns all combinations ($C$) of three candidate point sources from the table of sources phot returned by Photometry.Aperture.photometry, and the computed invariant $\mathscr M$ for each according to Eq. 3 from Beroiz, M., Cabral, J. B., & Sanchez, B. (2020).