ellipticity_from_cat

lsst.validate.drp.util.ellipticity_from_cat(cat, slot_shape='slot_Shape')

Calculate the ellipticity of the Shapes in a catalog from the 2nd moments.

Parameters:

cat : An afwtable catalog with ‘slot_Shape’ defined and ‘_xx’, ‘_xy’, ‘_yy’

entries for the target of ‘slot_Shape’. E.g., ‘slot_shape’ defined as ‘base_SdssShape’ And ‘base_SdssShape_xx’, ‘base_SdssShape_xy’, ‘base_SdssShape_yy’ defined.

slot_shape : str, optional

Specify what slot shape requested. Intended use is to get the PSF shape estimates by specifying ‘slot_shape=slot_PsfShape’ instead of the default ‘slot_shape=slot_Shape’.

Returns:

e, e1, e2 : complex, float, float

Complex ellipticity, real part, imaginary part