photutils.isophote.fit_upper_harmonic(phi, intensities, order)[source]

Fit upper harmonic function to a set of (angle, intensity) pairs.

With order set to 3 or 4, the resulting amplitudes, divided by the semimajor axis length and local gradient, measure the deviations from perfect ellipticity.

The harmonic function that is fit is:

\[y(phi, order) = y0 + An*\sin(order*phi) + Bn*\cos(order*phi)\]
phifloat or ndarray

The angle(s) along the elliptical path, going towards the positive y axis, starting coincident with the position angle. That is, the angles are defined from the semimajor axis that lies in the positive x quadrant.


The intensities measured along the elliptical path, at the angles defined by the phi parameter.


The order of the harmonic to be fitted.

y0, An, Bnfloat

The fitted harmonic values.