EnsquaredCurveOfGrowth

class photutils.profiles.EnsquaredCurveOfGrowth(data, xycen, half_sizes, *, error=None, mask=None, method='exact', subpixels=5)

Bases: ProfileBase

Class to create a curve of growth using concentric square apertures.

The ensquared curve of growth profile represents the square aperture flux as a function of the square half-size (half side length).

Parameters:

data2D ndarray

The 2D data array. The data should be background-subtracted. Non-finite values (e.g., NaN or inf) in the data or error array are automatically masked.

xycentuple of 2 floats

The (x, y) pixel coordinate of the source center.

half_sizes1D float ndarray

An array of the square half side lengths. half_sizes must be strictly increasing with a minimum value greater than zero, and contain at least 2 values. The spacing does not need to be constant. The full side length of each square aperture is 2 * half_sizes.

error2D ndarray, optional

The 1-sigma errors of the input data. error is assumed to include all sources of error, including the Poisson error of the sources (see calc_total_error). error must have the same shape as the input data. Non-finite values (e.g., NaN or inf) in the data or error array are automatically masked.

mask2D bool ndarray, optional

A boolean mask with the same shape as data where a True value indicates the corresponding element of data is masked. Masked data are excluded from all calculations.

method{‘exact’, ‘center’, ‘subpixel’}, optional

The method used to determine the pixel weights (the fraction of the pixel area covered by the aperture):

• 'exact' (default): Calculates the exact geometric overlap area. Weights are continuous in the range [0, 1].

• 'center': Binary weighting based on the pixel center. Weights are either 0 or 1. A pixel is included only if its center lies strictly inside the aperture; pixel centers lying exactly on the aperture boundary are excluded (weight 0).

• 'subpixel': Approximates the overlap by averaging binary samples on a subgrid. The number of samples is set by the subpixels parameter. Weights are discrete in the range [0, 1]. A subpixel is included only if its center lies strictly inside the aperture; subpixel centers lying exactly on the aperture boundary are excluded (weight 0).

subpixelsint, optional

The subsampling factor per axis used when method='subpixel'. Each pixel is divided into a grid of subpixels**2 subpixels to approximate the overlap. This parameter is ignored for other methods.

See also

CurveOfGrowth, EllipticalCurveOfGrowth

Examples

>>> import numpy as np
>>> from astropy.modeling.models import Gaussian2D
>>> from photutils.centroids import centroid_2dg
>>> from photutils.datasets import make_noise_image
>>> from photutils.profiles import EnsquaredCurveOfGrowth

Create an artificial single source. Note that this image does not have any background.

>>> gmodel = Gaussian2D(42.1, 47.8, 52.4, 4.7, 4.7, 0)
>>> yy, xx = np.mgrid[0:100, 0:100]
>>> data = gmodel(xx, yy)
>>> bkg_sig = 2.1
>>> noise = make_noise_image(data.shape, mean=0., stddev=bkg_sig, seed=0)
>>> data += noise
>>> error = np.zeros_like(data) + bkg_sig

Create the ensquared curve of growth.

>>> xycen = centroid_2dg(data)
>>> half_sizes = np.arange(1, 26)
>>> ecog = EnsquaredCurveOfGrowth(data, xycen, half_sizes, error=error)

>>> print(ecog.half_size)
[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
 25]

>>> print(ecog.profile)
[ 171.51682931  640.93965938 1328.92447125 2143.49339746 2954.67817356
 3718.43574763 4357.67409109 4845.38866928 5199.93124392 5481.4874771
 5641.60852855 5752.43870109 5791.01446371 5819.46039533 5832.44691816
 5825.39056549 5834.14890108 5833.42003487 5852.25143102 5856.59671815
 5869.46227464 5872.94734439 5868.92606685 5849.96903786 5839.55875017]

>>> print(ecog.profile_error)
[  4.2   8.4  12.6  16.8  21.   25.2  29.4  33.6  37.8  42.   46.2  50.4
  54.6  58.8  63.   67.2  71.4  75.6  79.8  84.   88.2  92.4  96.6 100.8
 105. ]

Normalize the profile and plot the normalized ensquared curve of growth.

(Source code, png, hires.png, pdf, svg)

Plot a couple of the apertures on the data.

(Source code, png, hires.png, pdf, svg)

Attributes Summary

apertures	A list of RectangularAperture objects used to measure the profile.
area	The unmasked area in each square aperture as a function of size as a 1D ndarray.
half_size	The profile half-sizes (half side lengths) in pixels as a 1D ndarray.
profile	The ensquared curve-of-growth profile as a 1D ndarray.
profile_error	The ensquared curve-of-growth profile errors as a 1D ndarray.
radius	The profile half-sizes (half side lengths) in pixels as a 1D ndarray.

Methods Summary

calc_ee_at_half_size(half_size)	Calculate the ensquared energy at a given half-size using a cubic interpolator based on the profile data.
calc_half_size_at_ee(ee)	Calculate the half-size at a given ensquared energy using a cubic interpolator based on the profile data.
normalize([method])	Normalize the profile.
plot([ax])	Plot the profile.
plot_error([ax])	Plot the profile errors.
unnormalize()	Unnormalize the profile back to the original state before any calls to normalize.

Attributes Documentation

apertures

A list of RectangularAperture objects used to measure the profile.

area

The unmasked area in each square aperture as a function of size as a 1D ndarray.

half_size

The profile half-sizes (half side lengths) in pixels as a 1D ndarray.

This is the same as the input half_sizes.

Note that these are the half side lengths of the square apertures used to measure the profile. The full side length of each square aperture is 2 * half_size. They can be used directly to measure the ensquared energy/flux at a given half-size.

profile

The ensquared curve-of-growth profile as a 1D ndarray.

profile_error

The ensquared curve-of-growth profile errors as a 1D ndarray.

If no error array was provided, an empty array with shape (0,) is returned.

radius

The profile half-sizes (half side lengths) in pixels as a 1D ndarray.

This is an alias for half_size.

Methods Documentation

calc_ee_at_half_size(half_size)

Calculate the ensquared energy at a given half-size using a cubic interpolator based on the profile data.

Note that this method assumes that input data has been normalized such that the total enclosed flux is 1 for an infinitely large half-size. You can also use the normalize method before calling this method to normalize the profile to be 1 at the largest input half_sizes.

Parameters:

half_sizefloat or 1D ndarray

The square half side length(s).

Returns:

eendarray

The ensquared energy at each half-size. Returns NaN for half-sizes outside the range of the profile data.

calc_half_size_at_ee(ee)

Calculate the half-size at a given ensquared energy using a cubic interpolator based on the profile data.

Note that this method assumes that input data has been normalized such that the total enclosed flux is 1 for an infinitely large half-size. You can also use the normalize method before calling this method to normalize the profile to be 1 at the largest input half_sizes.

This interpolator returns values only for regions where the ensquared curve-of-growth profile is monotonically increasing.

Parameters:

eefloat or 1D ndarray

The ensquared energy.

Returns:

half_sizendarray

The half-size at each ensquared energy. Returns NaN for ensquared energies outside the range of the profile data.

normalize(method='max')

Normalize the profile.

Parameters:

method{‘max’, ‘sum’}, optional

The method used to normalize the profile:

• 'max' (default): The profile is normalized such that its maximum value is 1.

• 'sum': The profile is normalized such that its sum (integral) is 1.

plot(ax=None, **kwargs)

Plot the profile.

Parameters:

axmatplotlib.axes.Axes or None, optional

The matplotlib axes on which to plot. If None, then the current Axes instance is used.

**kwargsdict, optional

Any keyword arguments accepted by matplotlib.pyplot.plot.

Returns:

lineslist of Line2D

A list of lines representing the plotted data.

plot_error(ax=None, **kwargs)

Plot the profile errors.

Parameters:

axmatplotlib.axes.Axes or None, optional

The matplotlib axes on which to plot. If None, then the current Axes instance is used.

**kwargsdict, optional

Any keyword arguments accepted by matplotlib.pyplot.fill_between.

Returns:

polymatplotlib.collections.PolyCollection or None

A PolyCollection containing the plotted polygons, or None if no errors were input.

unnormalize()

Unnormalize the profile back to the original state before any calls to normalize.