" : Currently, this is the only schema supported by the YamlChan class. It is defined
by the Space Telescope Science Institute. (see http://asdf-standard.readthedocs.io).
See below for details of the support this class provides for reading and writing ASDF
objects. In future, the YamlChan class may allow AST objects to be represented in other
ways (e.g. AST Native format).
The ASDF spectral_frame, temporal_frame and composite_frame classes are not supported.
Only the following celestial coordinate frames are supported: icrs, fk4, fk4noeterms, fk5, galactic, supergalactic, altaz, barycentricmeanecliptic.
Earth locations must be specified using the WGS84 ellipsoid.
Times must be specified in one of the following formats: iso, byear, jyear, jd, mjd.
Only the following transform classes are supported: identity, scale, multiplyscale, remap_axes, shift, compose, concatenate, constant, fix_inputs, affine, rotate2d, rotate_sequence_3d, rotate3d, linear1d, ortho_polynomial (chebyshev only), planar2d, polynomial. In addition, all sky projections are supported.
Only Frames, Mappings and FrameSets can be written.
Frames must be basic Frames or SkyFrames.
The following SkyFrame systems are not supported: GAPPT, HELIOECLIPTIC, J2000, UNKNOWN.