wfss

jwst.assign_wcs.nircam.wfss(input_model, reference_files)

Create the WCS pipeline for a NIRCAM grism observation.

Parameters:

input_modelImageModel

The input data model.

reference_filesdict

Mapping between reftype (keys) and reference file name (vals). Requires ‘distortion’, ‘filteroffset’, and ‘specwcs’ reference files.

Returns:

pipelinelist

The WCS pipeline, suitable for input into gwcs.wcs.WCS.

Notes

The tree in the grism reference file has a section for each order. Not sure if there will be a separate passband reference file needed for the wavelength scaling or wedge offsets.

The direct image the catalog has been created from was processed through resample, but the dispersed images have not been resampled. This is OK if the trace and dispersion solutions are defined with respect to the distortion-corrected image. The catalog from the combined direct image has object locations in in detector space and the RA DEC of the object on the sky.

The WCS information for the grism image plus the observed filter will be used to translate these to pixel locations for each of the objects. The grism images will then use their grism trace information to translate to detector space. The translation is assumed to be one-to-one for purposes of identifying the center of the object trace.

The extent of the trace for each object can then be calculated based on the grism in use (row or column). Where the left/bottom of the trace starts at t = 0 and the right/top of the trace ends at t = 1, as long as they have been defined as such by the team.

The extraction box is calculated to be the minimum bounding box of the object extent in the segmentation map associated with the direct image. The values of the min and max corners, taken from the computed minimum bounding box are saved in the photometry catalog in units of RA, DEC so they can be translated to pixels by the dispersed image’s imaging-wcs.