Feature skycoord

[lmichel]

Extension of the MIVOT feature answering #523.

If the MIVOT annotation block contains a valid instance of the mango:EpochPosition class, the dynamic object describing the mapped data can now generate a valid SkyCoord instance.

This feature makes quite easier the epoch propagation computation with the Astropy library.

from pyvo.mivot import MivotViewer
m_viewer = MivotViewer(path_to_votable)
mivot_instance = m_viewer.dm_instance
print(mivot_instance.get_SkyCoord())
<SkyCoord (ICRS): (ra, dec) in deg(52.26722684, 59.94033461)
          (pm_ra_cosdec, pm_dec) in mas / yr(-0.82, -1.85)>

Although not a standard at the time of writing, the class structure supported by the implementation must match the figure in the documentation:

The logic relies only on the vodml-id it finds in the annotation, without regard to the model structure; it can be easily extended to components of other models such as measurement.

• The space frame implementation supports FK4/5 (with equinox), ICRS and Galactic.
• The space frame standard location is not supported
• Time frame are not supported
• Epochs in year are processed as Jyear