CalcE¶

class lsst.analysis.tools.actions.vector.CalcE(*args, **kw)¶

Bases: VectorAction

Calculate a complex value representation of the ellipticity.

The complex ellipticity is typically defined as .. math:

e = |e|\exp{(j*2*theta)}
e = \\frac{((Ixx - Iyy) + j*(2*Ixy))}{(Ixx + Iyy)},

where j is the square root of -1 and Ixx, Iyy, Ixy are second-order central moments. This is sometimes referred to as distortion, and denoted by e = (e1, e2) in GalSim (see Eq. 4.4. of Bartelmann and Schneider, 2001). The other definition differs in normalization. It is referred to as shear, and denoted by g = (g1, g2) in GalSim (see Eq. 4.10 of Bartelmann and Schneider (2001). It is defined as .. math:

g = \\frac{((Ixx-Iyy)+j*(2*Ixy))}{(Ixx+Iyy+2\sqrt{(Ixx*Iyy-Ixy^{2})})}.

The shear measure is unbiased in weak-lensing shear, but may exclude some objects in the presence of noisy moment estimates. The distortion measure is biased in weak-lensing distortion, but does not suffer from selection artifacts.

See also

CalcE1
CalcE2

Notes

1. This is a shape measurement used for doing QA on the ellipticity of the sources.

2. For plotting purposes we might want to plot \(|E|*\exp{(i*theta)}\). If halvePhaseAngle config parameter is set to True, then the returned quantity therefore corresponds to \(|E|*\exp{(i*theta)}\).

References

[1] Bartelmann, M. and Schneider, P., “Weak gravitational lensing”, Physics Reports, vol. 340, no. 4–5, pp. 291–472, 2001. doi:10.1016/S0370-1573(00)00082-X; https://arxiv.org/abs/astro-ph/9912508

Attributes Summary

`colXx`	The column name to get the xx shape component from.
`colXy`	The column name to get the xy shape component from.
`colYy`	The column name to get the yy shape component from.
`component`	Which component of the ellipticity to return.
`ellipticityType`	The type of ellipticity to calculate (`str`, default `'distortion'`)
`halvePhaseAngle`	Divide the phase angle by 2? Suitable for quiver plots.

Methods Summary

`__call__`(data, **kwargs)	Call self as a function.
`getInputSchema`()	Return the schema an `AnalysisAction` expects to be present in the arguments supplied to the __call__ method.

Attributes Documentation

colXx¶: The column name to get the xx shape component from. (str, default '{band}_ixx')

colXy¶: The column name to get the xy shape component from. (str, default '{band}_ixy')

colYy¶: The column name to get the yy shape component from. (str, default '{band}_iyy')

component¶

Which component of the ellipticity to return. If None, return complex ellipticity values. (str, default None)

Allowed values:

'1': e1 or g1 (depending on ellipticityType)
'2': e2 or g2 (depending on ellipticityType)
'None': Field is optional

ellipticityType¶

The type of ellipticity to calculate (str, default 'distortion')

Allowed values:

'distortion': Distortion, defined as (Ixx - Iyy + 2j*Ixy)/(Ixx + Iyy)
'shear': Shear, defined as (Ixx - Iyy + 2j*Ixy)/(Ixx + Iyy + 2*sqrt(Ixx*Iyy - Ixy**2))
'None': Field is optional

halvePhaseAngle¶: Divide the phase angle by 2? Suitable for quiver plots. (bool, default False)

Methods Documentation

__call__(data: MutableMapping[str, ndarray[Any, dtype[ScalarType]] | Scalar | HealSparseMap], **kwargs) → ndarray[Any, dtype[ScalarType]]¶: Call self as a function.

getInputSchema() → HealSparseMap]]]¶

Return the schema an AnalysisAction expects to be present in the arguments supplied to the __call__ method.

Returns:

resultKeyedDataSchema: The schema this action requires to be present when calling this action, keys are unformatted.

Navigation

CalcE¶