# EllipticalAnnulus¶

class photutils.aperture.EllipticalAnnulus(positions, a_in, a_out, b_out, b_in=None, theta=0.0)[source]

An elliptical annulus aperture defined in pixel coordinates.

The aperture has a single fixed size/shape, but it can have multiple positions (see the positions input).

Parameters:
positionsarray_like

The pixel coordinates of the aperture center(s) in one of the following formats:

a_infloat

The inner semimajor axis of the elliptical annulus in pixels.

a_outfloat

The outer semimajor axis of the elliptical annulus in pixels.

b_outfloat

The outer semiminor axis of the elliptical annulus in pixels.

b_inNone or float, optional

The inner semiminor axis of the elliptical annulus in pixels. If None, then the the inner semiminor axis is calculated as:

$b_{in} = b_{out} \left(\frac{a_{in}}{a_{out}}\right)$
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.

Raises:
ValueErrorValueError

If inner semimajor axis (a_in) is greater than outer semimajor axis (a_out).

ValueErrorValueError

If either the inner semimajor axis (a_in) or the outer semiminor axis (b_out) is negative.

Examples

>>> from astropy.coordinates import Angle
>>> from photutils.aperture import EllipticalAnnulus

>>> theta = Angle(80, 'deg')
>>> aper = EllipticalAnnulus([10.0, 20.0], 3.0, 8.0, 5.0)
>>> aper = EllipticalAnnulus((10.0, 20.0), 3.0, 8.0, 5.0, theta=theta)

>>> pos1 = (10.0, 20.0)  # (x, y)
>>> pos2 = (30.0, 40.0)
>>> pos3 = (50.0, 60.0)
>>> aper = EllipticalAnnulus([pos1, pos2, pos3], 3.0, 8.0, 5.0)
>>> aper = EllipticalAnnulus((pos1, pos2, pos3), 3.0, 8.0, 5.0,
...                          theta=theta)


Attributes Summary

 a_in The inner semimajor axis in pixels. a_out The outer semimajor axis in pixels. area The exact analytical area of the aperture shape. b_in The inner semiminor axis in pixels. b_out The outer semiminor axis in pixels. bbox The minimal bounding box for the aperture. isscalar Whether the instance is scalar (i.e., a single position). positions The center pixel position(s). shape The shape of the instance. theta The counterclockwise rotation angle as an angular Quantity or value in radians from the positive x axis.

Methods Summary

 area_overlap(data, *[, mask, method, subpixels]) Return the area of overlap between the data and the aperture. Make an independent (deep) copy. do_photometry(data[, error, mask, method, ...]) Perform aperture photometry on the input data. plot([ax, origin]) Plot the aperture on a matplotlib Axes instance. to_mask([method, subpixels]) Return a mask for the aperture. to_sky(wcs) Convert the aperture to a SkyEllipticalAnnulus object defined in celestial coordinates.

Attributes Documentation

a_in

The inner semimajor axis in pixels.

a_out

The outer semimajor axis in pixels.

area
b_in

The inner semiminor axis in pixels.

b_out

The outer semiminor axis in pixels.

bbox

The minimal bounding box for the aperture.

If the aperture is scalar then a single BoundingBox is returned, otherwise a list of BoundingBox is returned.

isscalar

Whether the instance is scalar (i.e., a single position).

positions

The center pixel position(s).

shape

The shape of the instance.

theta

The counterclockwise rotation angle as an angular Quantity or value in radians from the positive x axis.

Methods Documentation

Return the area of overlap between the data and the aperture.

This method takes into account the aperture mask method, masked data pixels (mask keyword), and partial/no overlap of the aperture with the data. In other words, it returns the area that used to compute the aperture sum (assuming identical inputs).

Use the area method to calculate the exact analytical area of the aperture shape.

Parameters:
dataarray_like or Quantity

A 2D array.

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 the area overlap.

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

The method used to determine the overlap of the aperture on the pixel grid. Not all options are available for all aperture types. Note that the more precise methods are generally slower. The following methods are available:

• 'exact' (default): The 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'.

Returns:
areasfloat or array_like

The area (in pixels**2) of overlap between the data and the aperture.

copy()

Make an independent (deep) copy.

Perform aperture photometry on the input data.

Parameters:
dataarray_like or Quantity instance

The 2D array on which to perform photometry. data should be background subtracted.

errorarray_like or Quantity, optional

The pixel-wise Gaussian 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.

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. Not all options are available for all aperture types. Note that the more precise methods are generally slower. The following methods are available:

• 'exact' (default): The 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'.

Returns:
aperture_sums

The sums within each aperture.

aperture_sum_errs

The errors on the sums within each aperture.

Notes

RectangularAperture and RectangularAnnulus photometry with the “exact” method uses a subpixel approximation by subdividing each data pixel by a factor of 1024 (subpixels = 32). For rectangular aperture widths and heights in the range from 2 to 100 pixels, this subpixel approximation gives results typically within 0.001 percent or better of the exact value. The differences can be larger for smaller apertures (e.g., aperture sizes of one pixel or smaller). For such small sizes, it is recommend to set method='subpixel' with a larger subpixels size.

plot(ax=None, origin=(0, 0), **kwargs)

Plot the aperture on a matplotlib Axes instance.

Parameters:
axmatplotlib.axes.Axes or None, optional

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

originarray_like, optional

The (x, y) position of the origin of the displayed image.

**kwargsdict

Any keyword arguments accepted by matplotlib.patches.Patch.

Returns:
patchlist of Patch

A list of matplotlib patches for the plotted aperture. The patches can be used, for example, when adding a plot legend.

Return a mask for the aperture.

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

The method used to determine the overlap of the aperture on the pixel grid. Not all options are available for all aperture types. Note that the more precise methods are generally slower. The following methods are available:

• 'exact' (default): The 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'.

Returns:

A mask for the aperture. If the aperture is scalar then a single ApertureMask is returned, otherwise a list of ApertureMask is returned.

to_sky(wcs)[source]

Convert the aperture to a SkyEllipticalAnnulus object defined in celestial coordinates.

Parameters:
wcsWCS object

A world coordinate system (WCS) transformation that supports the astropy shared interface for WCS (e.g., astropy.wcs.WCS, gwcs.wcs.WCS).

Returns:
aperture

A SkyEllipticalAnnulus object.