EllipsePixelRegion

class regions.EllipsePixelRegion(center, width, height, angle=<Quantity 0. deg>, meta=None, visual=None)

Bases: PixelRegion

An ellipse in pixel coordinates.

Parameters:

centerPixCoord

The position of the center of the ellipse.

widthfloat

The width of the ellipse (before rotation) in pixels.

heightfloat

The height of the ellipse (before rotation) in pixels.

angleQuantity, optional

The rotation angle of the ellipse, measured anti-clockwise. If set to zero (the default), the width axis is lined up with the x axis.

metaRegionMeta or dict, optional

A dictionary that stores the meta attributes of the region.

visualRegionVisual or dict, optional

A dictionary that stores the visual meta attributes of the region.

Examples

from astropy.coordinates import Angle
from regions import PixCoord, EllipsePixelRegion
import matplotlib.pyplot as plt

fig, ax = plt.subplots(1, 1)

reg = EllipsePixelRegion(PixCoord(15, 10), width=16, height=10,
                         angle=Angle(30, 'deg'))
patch = reg.plot(ax=ax, facecolor='none', edgecolor='red', lw=2,
                 label='Ellipse')

ax.legend(handles=(patch,), loc='upper center')
ax.set_xlim(0, 30)
ax.set_ylim(0, 20)
ax.set_aspect('equal')

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

Attributes Summary

angle	The rotation angle measured anti-clockwise as a astropy.units.Quantity angle.
area	The exact analytical area of the region shape.
bounding_box	The minimal bounding box (RegionBoundingBox) enclosing the exact elliptical region.
center	The center pixel position as a PixCoord.
height	The height of the ellipse (before rotation) in pixels as a float.
meta	The meta attributes as a RegionMeta
visual	The visual attributes as a RegionVisual.
width	The width of the ellipse (before rotation) in pixels as a float.

Methods Summary

as_artist([origin])	Return a matplotlib patch object for the region (matplotlib.patches.Ellipse).
as_mpl_selector(ax[, active, sync, ...])	Return a matplotlib editable widget for this region (matplotlib.widgets.EllipseSelector).
contains(pixcoord)	Check whether a position or positions fall inside the region.
rotate(center, angle)	Rotate the region.
to_mask([mode, subpixels])	Return a mask for the region.
to_polygon([n_points])	Return a PolygonPixelRegion that approximates this ellipse.
to_sky(wcs)	Return a region defined in sky coordinates.
to_spherical_sky([wcs, ...])	Convert to an equivalent spherical SphericalSkyRegion instance.

Attributes Documentation

angle

The rotation angle measured anti-clockwise as a astropy.units.Quantity angle.

area

bounding_box

The minimal bounding box (RegionBoundingBox) enclosing the exact elliptical region.

center

The center pixel position as a PixCoord.

height

The height of the ellipse (before rotation) in pixels as a float.

meta

The meta attributes as a RegionMeta

visual

The visual attributes as a RegionVisual.

width

The width of the ellipse (before rotation) in pixels as a float.

Methods Documentation

as_artist(origin=(0, 0), **kwargs)

Return a matplotlib patch object for the region (matplotlib.patches.Ellipse).

Parameters:

originarray_like, optional

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

**kwargsdict

Any keyword arguments accepted by Ellipse. These keywords will override any visual meta attributes of this region.

Returns:

artistEllipse

A matplotlib ellipse patch.

as_mpl_selector(ax, active=True, sync=True, callback=None, drag_from_anywhere=False, **kwargs)

Return a matplotlib editable widget for this region (matplotlib.widgets.EllipseSelector).

Parameters:

axAxes

The matplotlib axes to add the selector to.

activebool, optional

Whether the selector should be active by default.

syncbool, optional

If True (the default), the region will be kept in sync with the selector. Otherwise, the selector will be initialized with the values from the region but the two will then be disconnected.

callbackcallable, optional

If specified, this function will be called every time the region is updated. This only has an effect if sync is True. If a callback is set, it is called for the first time once the selector has been created.

drag_from_anywherebool, optional

If True, the selector can be moved by clicking anywhere within its bounds, else only at the central anchor (only available with matplotlib 3.5 upwards; default: False).

**kwargsdict

Additional keyword arguments that are passed to matplotlib.widgets.EllipseSelector.

Returns:

selectormatplotlib.widgets.EllipseSelector

The matplotlib selector.

Notes

Once a selector has been created, you will need to keep a reference to it until you no longer need it. In addition, you can enable/disable the selector at any point by calling selector.set_active(True) or selector.set_active(False).

contains(pixcoord)

Check whether a position or positions fall inside the region.

Parameters:

pixcoordPixCoord

The position or positions to check.

rotate(center, angle)

Rotate the region.

Positive angle corresponds to counter-clockwise rotation.

Parameters:

centerPixCoord

The rotation center point.

angleAngle

The rotation angle.

Returns:

regionEllipsePixelRegion

The rotated region (which is an independent copy).

to_mask(mode='center', subpixels=5)

Return a mask for the region.

Parameters:

mode{‘center’, ‘exact’, ‘subpixels’}, optional

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

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

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

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

subpixelsint, optional

For the 'subpixel' mode, resample pixels by this factor in each dimension. That is, each pixel is divided into subpixels ** 2 subpixels.

Returns:

maskRegionMask

A mask for the region.

to_polygon(n_points=100)

Return a PolygonPixelRegion that approximates this ellipse.

Parameters:

n_pointsint, optional

The number of polygon vertices. Default is 100.

Returns:

polygonPolygonPixelRegion

A polygon region approximating the ellipse.

to_sky(wcs)

Return a region defined in sky coordinates.

Parameters:

wcsWCS

The world coordinate system transformation to use to convert from pixels to sky coordinates.

Returns:

sky_regionSkyRegion

The sky region.

Notes

The conversion between pixel and sky coordinates is an approximation. The pixel region shape is mapped to a sky region shape using the local pixel scale and angle at the region center. Projection effects over the extent of the region are not accounted for. The region shape type is always preserved (e.g., a CirclePixelRegion converts to a CircleSkyRegion).

For WCS with distortions (e.g., SIP), the local Jacobian matrix of the WCS transformation is used to compute directional scale factors and angle. For WCS without distortions, a local pixel scale and angle are computed using offset-based methods.

to_spherical_sky(wcs=None, include_boundary_distortions=False, n_points=None)

Convert to an equivalent spherical SphericalSkyRegion instance.

Parameters:

wcsWCS instance, optional

The world coordinate system transformation to use to convert between sky and pixel coordinates. Required if transforming with boundary distortions (if include_boundary_distortions is True). Ignored if boundary distortions not included.

include_boundary_distortionsbool, optional

If True, accounts for boundary distortions in spherical to planar conversions, by discretizing the boundary and converting the boundary polygon. Default is False, which converts to an equivalent idealized shape.

n_pointsint, optional

The number of polygon vertices for boundary discretization. This keyword will have effect unless include_boundary_distortions=True. Default is 100.

Returns:

spherical_sky_regionSphericalSkyRegion

A spherical sky region, with an equivalent shape (if include_boundary_distortions is False), or a discretized polygon of the boundary (if include_boundary_distortions is True).