Inconsistent interface for data access

[mcdittmar]

The path to the 'leaf' data from columns appears to depend on what sort of value is at the leaf:
Or maybe more to the point, how it is serialized.

• if has 'unit'(?):
  • see warnings from astropy/table.py:
    • "UserWarning: dropping mask in Quantity column '_color': masked Quantity not supported"
  • column values type is "astropy.units.quantity.Quantity
    • access data via: prop.measure.coord.hardness_ratio.value[row] == float64
    • access data via: prop.measure.coord.hardness_ratio[row] == Quantity
• otherwise:
  • column values type is "astropy.table.column.MaskedColumn"
    • access data via: prop.measure.coord.hardness_ratio[row] == float64

dmusecases:standard_properties

• gaia - color is a difference in magnitudes, so has unit='mag'
• 4xmm - hardness ratio is dimensionless, so no units.