SpectralFrame ignoring reference_position

[braingram]

While testing schema with defaults I encountered unexpected behavior when loading an asdf file with a saved spectral frame.

First running:

import asdf
import gwcs

tree = {
    'sf': gwcs.coordinate_frames.SpectralFrame(
        reference_position="GEOCENTER")
}
af = asdf.AsdfFile(tree)
af.write_to('foo.asdf')

Will generate an asdf file with contents:

#ASDF 1.0.0
#ASDF_STANDARD 1.5.0
%YAML 1.1
%TAG ! tag:stsci.edu:asdf/
--- !core/asdf-1.1.0
asdf_library: !core/software-1.0.0 {author: The ASDF Developers, homepage: 'http://github.com/asdf-format/asdf',
  name: asdf, version: 2.13.1.dev71+gf8efb2a.d20221012}
history:
  extensions:
  - !core/extension_metadata-1.0.0
    extension_class: asdf.extension.BuiltinExtension
    software: !core/software-1.0.0 {name: asdf, version: 2.13.1.dev71+gf8efb2a.d20221012}
  - !core/extension_metadata-1.0.0
    extension_class: gwcs.extension.GWCSExtension
    software: !core/software-1.0.0 {name: gwcs, version: 0.17.1}
sf: !<tag:stsci.edu:gwcs/spectral_frame-1.0.0>
  axes_names: ['']
  axes_order: [0]
  axis_physical_types: ['custom:dimensionless']
  name: SpectralFrame
  reference_position: geocenter
  unit: [!unit/unit-1.0.0 '']
...

However, loading this file ignores reference_position entirely:

import asdf

af = asdf.open('foo.asdf')
print(af['sf'].reference_position)

Prints None

I believe the cause of the error is that reference_position is not propagated through FrameConverter._from_yaml_tree:

gwcs/gwcs/converters/wcs.py

Lines 46 to 69 in baef572

	def _from_yaml_tree(self, node, tag, ctx):
	kwargs = {'name': node['name']}
	if 'axes_type' in node and 'naxes' in node:
	kwargs.update({
	'axes_type': node['axes_type'],
	'naxes': node['naxes']})
	if 'axes_names' in node:
	kwargs['axes_names'] = node['axes_names']
	if 'reference_frame' in node:
	kwargs['reference_frame'] = node['reference_frame']
	if 'axes_order' in node:
	kwargs['axes_order'] = tuple(node['axes_order'])
	if 'unit' in node:
	kwargs['unit'] = tuple(node['unit'])
	if 'axis_physical_types' in node:
	kwargs['axis_physical_types'] = tuple(node['axis_physical_types'])
	return kwargs

called from SpectralFrameConverter:

gwcs/gwcs/converters/wcs.py

Line 135 in baef572

node = self._from_yaml_tree(node, tag, ctx)

I looked back several versions and believe this issue might be older than 0.9 (for older versions the issue was with the old asdf types instead of converters).

[Cadair]

I think #457 fixed this.

[nden]

To clarify - the original design was following the IVOA spec for spectral coordinates which defines a reference position. The current implementation uses astropy.coordinates.SpectralCoord.
Testing the converter shows it doesn't serialize some of the SectralCoord attributes. I'll open an issue on asdf-astropy.