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 overlap of the aperture on the pixel grid:

• 'exact' (default): The exact fractional overlap of the aperture and each pixel is calculated. The aperture weights will contain values between 0 and 1.

• 'center': A pixel is considered to be entirely in or out of the aperture depending on whether its center is in or out of the aperture. The aperture weights will contain values only of 0 (out) and 1 (in).

• 'subpixel': A pixel is divided into subpixels (see the subpixels keyword), each of which are considered to be entirely in or out of the aperture depending on whether its center is in or out of the aperture. If subpixels=1, this method is equivalent to 'center'. The aperture weights will contain values between 0 and 1.

subpixelsint, optional

For the 'subpixel' method, resample pixels by this factor in each dimension. That is, each pixel is divided into subpixels**2 subpixels. This keyword is ignored unless method='subpixel'.

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)
[ 171.35182895  640.63717997 1328.55725483 2142.84258293 2954.12152275
 3717.5208724  4356.82277842 4844.97997426 5199.74452363 5480.78438494
 5641.63617089 5751.92491894 5790.90751883 5819.30778391 5832.38652883
 5825.14679788 5833.55196333 5833.54737611 5851.79194687 5856.58494602
 5869.76637039 5872.91078217 5868.62195688 5850.11085443 5838.889818  ]

>>> 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.