Step Arguments

The assign_wcs step has the following optional arguments to control the behavior of the processing.

--sip_approx (boolean, default=True)

A flag to enable the computation of a SIP approximation for imaging modes.

--sip_degree (integer, max=6, default=None)

Polynomial degree for the forward SIP fit. “None” uses the best fit.

--sip_max_pix_error (float, default=0.01)

Maximum error for the SIP forward fit, in units of pixels. Ignored if sip_degree is set to an explicit value.

--sip_inv_degree (integer, max=6, default=None)

Polynomial degree for the inverse SIP fit. “None” uses the best fit.

--sip_max_inv_pix_error (float, default=0.01)

Maximum error for the SIP inverse fit, in units of pixels. Ignored if sip_inv_degree is set to an explicit value.

--sip_npoints (integer, default=12)

Number of points for the SIP fit.

--slit_y_low (float, default=-0.55)

Lower edge of a NIRSpec slit in slit units (see below).

--slit_y_high (float, default=0.55)

Upper edge of a NIRSpec slit in slit units.

Slit units are specified as a fraction of the nominal slit or shutter height. In these relative units, -0.5 is the nominal top edge of the slit open area in the image frame, 0.0 is the center of the slit, and 0.5 is the nominal bottom edge of the slit open area in the image frame.

Set the slit_y_low value to a larger negative value to include more pixels at the top of a slit bounding box; a smaller negative value to to include fewer pixels.

Set the slit_y_high value to a larger positive value to include more pixels at the bottom of a slit bounding box; a smaller positive value to to include fewer pixels.

For MSA slits in NIRSpec MOS mode, the slit units are relative to a single open shutter height, not a full “slitlet” composed of multiple shutters. For this mode, the slit_y_low and slit_y_high values determine the padding of the slitlet edges relative to the centers of the edge shutters. An additional margin of half a shutter is also automatically added to the slit boundaries specified by these parameters, corresponding to a couple extra detector pixels at the top and bottom of each slitlet.

Please note that significantly expanding the slit limit values may introduce contamination from adjacent open slits when the slit images are extracted in the extract_2d step, and/or may expand the slits into regions that cannot be flat fielded in the flat_field step. These parameters should be used with caution.