Add custom step to WCS pipeline and serialize with ASDF

gwcs_pipeline.py

#!/usr/bin/env python

import os
import sys
import copy

import asdf
from astropy import modeling


class IdentityTrans(modeling.Fittable2DModel):
    inputs = ('x', 'y')
    outputs = ('x1', 'y1')

    p = modeling.Parameter(default=1)

    @staticmethod
    def evaluate(x, y, p):
        return x, y


def process(filename):

    af = asdf.open(filename)
    wcs = copy.deepcopy(af['meta']['wcs'])
    wcs.insert_transform('world', IdentityTrans(p=2))
    af['meta']['wcs'] = wcs
    return af


def main():

    if len(sys.argv) != 2:
        script = os.path.basename(sys.argv[0])
        sys.stderr.write(f'USAGE: {script} <filename>\n')
        sys.exit(1)

    new_af = process(sys.argv[1])
    new_af.write_to('new.asdf')


if __name__ == '__main__':
    main()