CircleAnnulusSkyRegion

class regions.CircleAnnulusSkyRegion(center, inner_radius, outer_radius, meta=None, visual=None)

Bases: SkyRegion

A circular annulus in sky coordinates.

Parameters:

centerSkyCoord

The position of the center of the annulus.

inner_radiusQuantity

The inner radius of the annulus in angular units.

outer_radiusQuantity

The outer radius of the annulus in angular units.

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.

Attributes Summary

center	The center position as a astropy.coordinates.SkyCoord.
inner_radius	The inner radius as a astropy.units.Quantity angle.
meta	The meta attributes as a RegionMeta
outer_radius	The outer radius as a astropy.units.Quantity angle.
visual	The visual attributes as a RegionVisual.

Methods Summary

to_pixel(wcs)	Return the equivalent region defined in pixel coordinates.
to_polygon(wcs[, n_points])	Return a CompoundSkyRegion of two PolygonSkyRegion objects that approximates this annulus.
to_spherical_sky([wcs, ...])	Convert to an equivalent spherical SphericalSkyRegion instance.

Attributes Documentation

center

The center position as a astropy.coordinates.SkyCoord.

inner_radius

The inner radius as a astropy.units.Quantity angle.

meta

The meta attributes as a RegionMeta

outer_radius

The outer radius as a astropy.units.Quantity angle.

visual

The visual attributes as a RegionVisual.

Methods Documentation

to_pixel(wcs)

Return the equivalent region defined in pixel coordinates.

Parameters:

wcsWCS

The world coordinate system transformation to use to convert between sky and pixel coordinates.

Returns:

pixel_regionPixelRegion

A pixel region.

Notes

The conversion between sky and pixel coordinates is an approximation. The sky region shape is mapped to a pixel 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 CircleSkyRegion converts to a CirclePixelRegion).

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_polygon(wcs, n_points=100)

Return a CompoundSkyRegion of two PolygonSkyRegion objects that approximates this annulus.

Parameters:

wcsWCS

The WCS to use for the sky-to-pixel-to-sky conversion.

n_pointsint, optional

The number of polygon vertices for each circle. Default is 100.

Returns:

polygonCompoundSkyRegion

A compound region of two polygon regions approximating the annulus.

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).