SkyProjection#

final class lsst.images.SkyProjection(pixel_to_sky, fits_approximation=None)#

Bases: Generic

A transform from pixel coordinates to sky coordinates.

Parameters:

pixel_to_sky (Transform[TypeVar(F, bound= Frame), SkyFrame]) – A low-level transform that maps pixel coordinates to sky coordinates.
fits_approximation (Optional[Transform[TypeVar(F, bound= Frame), SkyFrame]], default: None) – An approximation to pixel_to_sky that is guaranteed to have a as_fits_wcs method that does not return None. This should not be provided if pixel_to_sky is itself representable as a FITS WCS.

Notes

Transform is conceptually immutable (the internal AST Mapping should never be modified in-place after construction), and hence does not need to be copied when any object that holds it is copied.

Attributes Summary

`fits_approximation`	An approximation to this projection that is guaranteed to have an `as_fits_wcs` method that does not return `None`.
`pixel_bounds`	The region that bounds valid pixel points (`Bounds` \| `None`).
`pixel_frame`	Coordinate frame for the pixel grid.
`pixel_to_sky_transform`	Low-level transform from pixel to sky coordinates (`Transform`).
`sky_frame`	Coordinate frame for the sky.
`sky_to_pixel_transform`	Low-level transform from sky to pixel coordinates (`Transform`).

Methods Summary

`as_astropy`([bbox])	Return an `astropy.wcs` view of this `SkyProjection`.
`as_fits_wcs`(bbox[, allow_approximation])	Return a FITS WCS representation of this projection, if possible.
`from_ast_frame_set`(ast_frame_set, pixel_frame)	Construct a sky projection from an AST FrameSet.
`from_fits_wcs`(fits_wcs, pixel_frame[, ...])	Construct a transform from a FITS WCS.
`from_legacy`(sky_wcs, pixel_frame[, pixel_bounds])	Construct a transform from a legacy `lsst.afw.geom.SkyWcs`.
`pixel_to_sky`([point, x, y])	Transform one or more pixel points to sky coordinates.
`serialize`(archive, *[, use_frame_sets])	Serialize a projection to an archive.
`show`([simplified, comments])	Return the AST native representation of the transform.
`sky_to_pixel`(sky)	Transform one or more sky coordinates to pixels.
`to_legacy`()	Convert to a legacy `lsst.afw.geom.SkyWcs` instance.

Attributes Documentation

fits_approximation#: An approximation to this projection that is guaranteed to have an as_fits_wcs method that does not return None.

pixel_bounds#: The region that bounds valid pixel points (Bounds | None).

pixel_frame#: Coordinate frame for the pixel grid.

pixel_to_sky_transform#: Low-level transform from pixel to sky coordinates (Transform).

sky_frame#: Coordinate frame for the sky.

sky_to_pixel_transform#: Low-level transform from sky to pixel coordinates (Transform).

Methods Documentation

as_astropy(bbox=None)#

Return an astropy.wcs view of this SkyProjection.

Parameters:: bbox (Box | None, default: None) – Bounding box of the array the view will describe. This projection object is assumed to work on the same coordinate system in which bbox is defined, while the Astropy view will consider the first row and column in that box to be (0, 0).
Return type:: SkyProjectionAstropyView

Notes

This returns an object that satisfies the astropy.wcs.wcsapi.BaseHighLevelWCS and astropy.wcs.wcsapi.BaseLowLevelWCS interfaces while evaluating the underlying SkyProjection itself. It is not an astropy.wcs.WCS instance, which is a type that also satisfies those interfaces but only supports FITS WCS representations (see as_fits_wcs).

as_fits_wcs(bbox, allow_approximation=False)#

Return a FITS WCS representation of this projection, if possible.

Parameters:

bbox (Box) – Bounding box of the array the FITS WCS will describe. This transform object is assumed to work on the same coordinate system in which bbox is defined, while the FITS WCS will consider the first row and column in that box to be (0, 0) (in Astropy interfaces) or (1, 1) (in the FITS representation itself).
allow_approximation (bool, default: False) – If True and this SkyProjection holds a FITS approximation to itself, return that approximation.

Return type:

WCS | None

static from_ast_frame_set(ast_frame_set, pixel_frame, pixel_bounds=None)#

Construct a sky projection from an AST FrameSet.

The current frame of the FrameSet must be an AST SkyFrame. Its coordinate system is forced to ICRS (AST adjusts the mapping automatically) so the resulting Projection is always in ICRS regardless of the original sky system.

Parameters:

ast_frame_set (FrameSet) – An AST FrameSet whose base frame is pixel coordinates and whose current frame is a SkyFrame (in any supported sky coordinate system).
pixel_frame (TypeVar(F, bound= Frame)) – Coordinate frame for the pixel grid.
pixel_bounds (Bounds | None, default: None) – The region that bounds valid pixels for this transform.

Raises:

ValueError – If the current frame of the FrameSet is not a SkyFrame.

Return type:

SkyProjection[TypeVar(F, bound= Frame)]

static from_fits_wcs(fits_wcs, pixel_frame, pixel_bounds=None, x0=0, y0=0)#

Construct a transform from a FITS WCS.

Parameters:

fits_wcs (WCS) – FITS WCS to convert.
pixel_frame (TypeVar(F, bound= Frame)) – Coordinate frame for the pixel grid.
pixel_bounds (Bounds | None, default: None) – The region that bounds valid pixels for this transform.
x0 (int, default: 0) – Logical coordinate of the first column in the array this WCS relates to world coordinates.
y0 (int, default: 0) – Logical coordinate of the first column in the array this WCS relates to world coordinates.

Return type:

SkyProjection[TypeVar(F, bound= Frame)]

Notes

The x0 and y0 parameters reflect the fact that for FITS, the first row and column are always labeled (1, 1), while in Astropy and most other Python libraries, they are (0, 0). The types in this package (e.g. Image, Mask) allow them to be any pair of integers.