GetWCSAdjustStep

This step calculates shifts to get good relative alignment between tiles in a mosaic. Since longer wavelengths may not have sources (and hence astrometry may fail catastrophically), we can instead defined a reference band to calculate a shift per-visit (since JWST cycles between filters), and apply that shift to all tiles in that visit. Our testing shows that taking a long NIRCam band that is ideally stellar dominated (i.e. F300M) works best for NIRCam, and a shorter wavelength, non-PAH-dominated MIRI band (i.e. F1000W) is ideal for MIRI.

API

class pjpipe.GetWCSAdjustStep(directory, progress_dict, target, alignment_dir, bands=None, alignment_catalogs=None, group_dithers=None, tweakreg_parameters=None, overwrite=False)[source]

Gets a table of WCS corrections to apply to visit groups

Experience has shown that the relative JWST guide star uncertainty is very small, but there are significant absolute corrections between guide stars. Thus, we can use the same visit as a correction for all visits, for example using F770W/F1000W at F2100W where tweakreg doesn’t work so well.

Here, we take some template bands and loop over with tweakreg, writing out a table of shifts/matrices to apply to other bands. For multiple dithers etc., will take an average correction

Parameters:

  • directory – Directory of target

  • progress_dict – The progress dictionary the pipeline builds up. This is used to figure out what subdirectories we should be looking in

  • target – Target to consider

  • alignment_dir – Directory for alignment catalogs

  • bands – List of target bands to pull corrections out for

  • alignment_catalogs – Dictionary mapping targets to alignment catalogs

  • group_dithers – Which band type (e.g. nircam) to group up dithers for and find a single correction. Defaults to None, which won’t group up anything

  • tweakreg_parameters – Dictionary of parameters to pass to tweakreg. Defaults to None, which will use observatory defaults

  • overwrite – Whether to overwrite or not. Defaults to False

do_step()[source]

Run the WCS adjust step

get_visit_transforms()[source]

Get transforms per-visit, running tweakreg and pulling out corrections