sep.kron_radius

sep.kron_radius(data, x, y, a, b, theta, r, mask=None, maskthresh=0.0)

Calculate Kron “radius” within an ellipse.

The Kron radius is given by

\[\sum_i r_i I(r_i) / \sum_i I(r_i)\]

where the sum is over all pixels in the aperture and the radius is given in units of a and b: r_i is the distance to the pixel relative to the distance to the ellipse specified by a, b, theta. Equivalently, after converting the ellipse parameters to their coefficient representation, r_i is given by

\[r_i^2 = cxx(x_i - x)^2 + cyy(y_i - y)^2 + cxx(x_i - x)(y_i - y)\]

Parameters:

data : ndarray

Data array.

x, y : array_like

Ellipse center(s).

a, b, theta : array_like

Ellipse parameters.

r : array_like

“Radius” of ellipse over which to integrate. If the ellipse extent correponds to second moments of an object, this is the number of “isophotal radii” in Source Extractor parlance. A Fixed value of 6 is used in Source Extractor.

mask : numpy.ndarray, optional

An optional mask.

maskthresh : float, optional

Pixels with mask > maskthresh will be ignored.

Returns:

kronrad : array_like

The Kron radius.

flag : array_like

Integer value indicating conditions about the aperture or how many masked pixels it contains.