Input Files#

KBMOD expects Vera C. Rubin Science Pipelines calexp-style data with at least a science and variance plane for each image. The core unit of data is the WorkUnit object, which holds the images and related metadata. WorkUnits objects can be created from a variety of sources including a set of multi-extension FITS files or references to the data’s location on a Butler instance. They can also be saved to disk and reloaded for future analyis.

WorkUnit Files#

The WorkUnit objects provide functions for writing to and loading from files. In addition to image data, the WorkUnit includes configuration data for the run and all necessary metadata (e.g. the WCS). To load a WorkUnit from a file, use:

my_wu = WorkUnit.from_fits(input_filename)

The images in a WorkUnit can either be in their original frame or reprojected to a common pixel grid. If they have been reprojected, the object’s reprojected is set to true. Reprojected sets of images have additional metadata, such as a mapping for the image’s index to those of the constituent images from which it was created.

The metadata for the original images is stored in an AstroPy Table in the org_img_meta attribute. This contains details such as each image’s WCS, data location and filter.

Butler#

TODO

FITS Files#

If loading data from raw FITS files, these must be Vera C. Rubin Science Pipelines calexp-style FITS files that contain:

  • photometrically and astometrically calibrated single-CCD image, usually referred to as the “science image”,

  • variance image, representing per-pixel noise levels, and a

  • pixel bitmask

stored in 1st, 2nd and 3rd header extension/plane respectively. The zeroth header extension is expected to contain the image metadata. A single FITS file can be loaded with the load_deccam_layered_image() function, which takes the file name and an optional numpy array of the PSF kernel and produces a LayeredImagePy.

To build an ImageCollection from multiple FITS files, use the class’s fromDir() function. The images within a single run are expected to be warped, i.e. geometrically transformed to a set of images with a consistent and uniform relationship between sky coordinates and image pixels on a shared pixel grid.