# Description¶

jwst.assign_mtwcs is run in the beginning of the level 3 JWST pipeline. It assigns a WCS to a Moving Target exposure. The table below defines the keywords specific to exposures with moving targets:

FITS keyword

Data model attribute

Type (Value)

Description

TARGTYPE

meta.target.type

string (moving)

Type of target

MT_RA, MT_DEC

meta.wcsinfo.mt_ra, meta.wcsinfo.mt_dec

number, number

Average right ascension and declination of the moving target during exposure [deg]

MT_AVRA, MT_AVDEC

meta.wcsinfo.mt_avra, meta.wcsinfo.mt_avdec

number, number

Right ascension and declination of the moving target averaged between exposures [deg]

The step takes the original science WCS pipeline and adds another step to it such that the output_frame of the final WCS is centered at the average location of the moving target specified by (MT_AVRA, MT_AVDEC).

The transform of original WCS associated with the science aperture pointing can be accessed by executing:

sci_transform = model.meta.wcs.get_transform('detector', 'world')