NIRISS GR700XD model PSFs in webbpsf

[obi-wan76]

This is a follow-up from an email about this issue.
The model in webbpsf for the GR700XD grating still uses the original prototype Bach grating parameters, not the flight LLNL grating.
https://github.com/spacetelescope/webbpsf/blob/develop/webbpsf/optics.py#L280

I'll contact people from the niriss team for assistant on this.

[mperrin]

Note that the optic class in webbpsf does have an option for the LLNL grating, with at least some of the parameters adjusted for that, at least partially, as of ~2014-2015 emails. That gives a starting place for continuing from.

Currently, trying to invoke it runs into a NotImplementedError:

> grating = webbpsf.optics.NIRISS_GR700XD_Grism(which='LLNL')


File ~/Dropbox (Personal)/Documents/software/webbpsf/webbpsf/optics.py:404, in NIRISS_GR700XD_Grism.__init__(self, name, which, **kwargs)
    398 def __init__(self, name='GR700XD', which='Bach',
    399              # cylinder_radius=22.85,  cylinder_sag_mm=4.0, rotation_angle=92.25, rotate_mask=False, transmission=None,
    400              **kwargs):
    401     # Initialize the base optical element with the pupil transmission and zero OPD
    403     if which == 'LLNL':
--> 404         raise NotImplementedError("Rotated field mask for LLNL grism not yet implemented!")
    405     elif which == 'Bach':
    406         transmission = os.path.join(utils.get_webbpsf_data_path(), "NIRISS/optics/MASKGR700XD.fits.gz")

NotImplementedError: Rotated field mask for LLNL grism not yet implemented!

That slightly confuses me though, in two ways. First, maybe that error text is just mislabeled because it needs a pupil mask, not a field mask. Secondly, even though there's a path defined for a mask file for the Bach grating, it doesn't actually use that file at all; instead there's a transmission mask defined analytically in the get_transmission function.

In any case the place to start will be tracking down the relevant as-built information for the optic design of the prism itself and also the pupil stop geometry around it.