EllipticalCurveOfGrowth#

class photutils.profiles.EllipticalCurveOfGrowth(data, xycen, radii, axis_ratio, *, theta=0.0, error=None, mask=None, method='exact', subpixels=5)[source]#

Bases: ProfileBase

Class to create a curve of growth using concentric elliptical apertures with a fixed axis ratio and orientation.

The elliptical curve of growth profile represents the elliptical aperture flux as a function of the semimajor axis 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.

radii1D float ndarray

An array of the ellipse semimajor-axis lengths. radii 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.

axis_ratiofloat

The ratio of the semiminor axis to the semimajor axis (b / a). Must be in the range 0 < axis_ratio <= 1.

thetafloat or Quantity, optional

The rotation angle as an angular quantity (Quantity or Angle) or value in radians (as a float) from the positive x axis. The rotation angle increases counterclockwise.

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, EnsquaredCurveOfGrowth

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 EllipticalCurveOfGrowth

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

>>> gmodel = Gaussian2D(42.1, 47.8, 52.4, 9.4, 4.7, np.deg2rad(42))
>>> 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 elliptical curve of growth with an axis ratio of 0.5 and a rotation angle of 42 degrees.

>>> xycen = centroid_2dg(data)
>>> radii = np.arange(1, 40)
>>> ecog = EllipticalCurveOfGrowth(data, xycen, radii, axis_ratio=0.5,
...                                theta=np.deg2rad(42), error=error)

>>> print(ecog.radius)
[ 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 26 27 28 29 30 31 32 33 34 35 36 37 38 39]

>>> print(ecog.profile)
[   67.39762867   267.711181     588.47524874  1021.31994307
  1546.53867489  2152.12698084  2824.97954482  3541.64650208
  4284.363828    5040.93586551  5777.06397177  6488.33779084
  7179.10371288  7826.17773764  8418.08027957  8948.7310004
  9418.56480323  9810.0373925  10163.11467352 10477.42357537
 10731.89184641 10920.11723061 11092.34059512 11235.12552706
 11347.43721424 11454.03577845 11520.64656354 11555.89668261
 11571.27935302 11583.89774142 11605.79810845 11639.93073462
 11648.27293403 11660.34772581 11662.89065496 11643.07787619
 11630.36674411 11636.61537567 11636.60448497]

>>> print(ecog.profile_error)
[  2.63195969   5.26391938   7.89587907  10.52783875  13.15979844
  15.79175813  18.42371782  21.05567751  23.6876372   26.31959688
  28.95155657  31.58351626  34.21547595  36.84743564  39.47939533
  42.11135501  44.7433147   47.37527439  50.00723408  52.63919377
  55.27115346  57.90311314  60.53507283  63.16703252  65.79899221
  68.4309519   71.06291159  73.69487127  76.32683096  78.95879065
  81.59075034  84.22271003  86.85466972  89.4866294   92.11858909
  94.75054878  97.38250847 100.01446816 102.64642785]

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

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

../_images/photutils-profiles-EllipticalCurveOfGrowth-1.png

Plot a couple of the apertures on the data.

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

../_images/photutils-profiles-EllipticalCurveOfGrowth-2.png

Attributes Summary

apertures

A list of EllipticalAperture objects used to measure the profile.

area

The unmasked area in each elliptical aperture as a function of semimajor axis as a 1D ndarray.

profile

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

profile_error

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

radius

The profile semimajor-axis lengths in pixels as a 1D ndarray.

Methods Summary

calc_ee_at_radius(radius)

Calculate the encircled energy at a given semimajor-axis length using a cubic interpolator based on the profile data.

calc_radius_at_ee(ee)

Calculate the semimajor-axis length at a given encircled 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 EllipticalAperture objects used to measure the profile.

area#

The unmasked area in each elliptical aperture as a function of semimajor axis as a 1D ndarray.

profile#

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

profile_error#

The elliptical 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 semimajor-axis lengths in pixels as a 1D ndarray.

This is the same as the input radii.

Note that these are the semimajor-axis lengths of the elliptical apertures used to measure the profile. Thus, they are the semimajor-axis values that enclose the given flux.

Methods Documentation

calc_ee_at_radius(radius)[source]#

Calculate the encircled energy at a given semimajor-axis length 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 radius. You can also use the normalize method before calling this method to normalize the profile to be 1 at the largest input radii.

Parameters:
radiusfloat or 1D ndarray

The semimajor-axis length(s).

Returns:
eendarray

The encircled energy at each radius. Returns NaN for radii outside the range of the profile data.

calc_radius_at_ee(ee)[source]#

Calculate the semimajor-axis length at a given encircled 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 radius. You can also use the normalize method before calling this method to normalize the profile to be 1 at the largest input radii.

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

Parameters:
eefloat or 1D ndarray

The encircled energy.

Returns:
radiusndarray

The semimajor-axis length at each encircled energy. Returns NaN for encircled 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.