EllipseSample

class photutils.isophote.EllipseSample(image, sma, x0=None, y0=None, astep=0.1, eps=0.2, position_angle=0.0, sclip=3.0, nclip=0, linear_growth=False, integrmode='bilinear', geometry=None)

Bases: object

Class to sample image data along an elliptical path.

The image intensities along the elliptical path can be extracted using a selection of integration algorithms.

The geometry attribute describes the geometry of the elliptical path.

Parameters:

image2D ndarray

The input image.

smafloat

The semimajor axis length in pixels.

x0, y0float, optional

The (x, y) coordinate of the ellipse center.

astepfloat, optional

The step value for growing/shrinking the semimajor axis. It can be expressed either in pixels (when linear_growth=True) or as a relative value (when linear_growth=False). The default is 0.1.

epsfloat, optional

The ellipticity of the ellipse. The default is 0.2.

pafloat, optional

The position angle of ellipse in relation to the positive x axis of the image array (rotating towards the positive y axis). The default is 0.

sclipfloat, optional

The sigma-clip sigma value. The default is 3.0.

nclipint, optional

The number of sigma-clip iterations. Set to zero to skip sigma-clipping. The default is 0.

linear_growthbool, optional

The semimajor axis growing/shrinking mode. The default is False.

integrmode{‘bilinear’, ‘nearest_neighbor’, ‘mean’, ‘median’}, optional

The area integration mode. The default is ‘bilinear’.

geometryEllipseGeometry instance or None

The geometry that describes the ellipse. This can be used in lieu of the explicit specification of parameters sma, x0, y0, eps, etc. In any case, the EllipseGeometry instance becomes an attribute of the EllipseSample object. The default is None.

Attributes:

values2D ndarray

The sampled values as a 2D array, where the rows contain the angles, radii, and extracted intensity values, respectively.

meanfloat

The mean intensity along the elliptical path.

geometryEllipseGeometry instance

The geometry of the elliptical path.

gradientfloat

The local radial intensity gradient.

gradient_errorfloat

The error associated with the local radial intensity gradient.

gradient_relative_errorfloat

The relative error associated with the local radial intensity gradient.

sector_areafloat

The average area of the sectors along the elliptical path from which the sample values were integrated.

total_pointsint

The total number of sample values that would cover the entire elliptical path.

actual_pointsint

The actual number of sample values that were taken from the image. It can be smaller than total_points when the ellipse encompasses regions outside the image, or when sigma-clipping removed some of the points.

Methods Summary

coordinates()	Return the (x, y) coordinates associated with each sampled point.
extract()	Extract sample data by scanning an elliptical path over the image array.
update([fixed_parameters])	Update this EllipseSample instance.

Methods Documentation

coordinates()

Return the (x, y) coordinates associated with each sampled point.

Returns:

x, y1D ndarray

The x and y coordinate arrays.

extract()

Extract sample data by scanning an elliptical path over the image array.

Returns:

result2D ndarray

The rows of the array contain the angles, radii, and extracted intensity values, respectively.

update(fixed_parameters=None)

Update this EllipseSample instance.

This method calls the extract() method to get the values that match the current geometry attribute, and then computes the the mean intensity, local gradient, and other associated quantities.