SkyCell

class romancal.skycell.skymap.SkyCell(index: int | None, skymap: SkyMap = None)[source]

Bases: object

Square subregion of a projection region, 4.6 arcminutes per side.

Parameters:

index (int) – Index in the global sky map.
skymap (SkyMap) – sky map instance (defaults to global SKYMAP)

Attributes Summary

`area`
`data`	Skycell data.
`index`	index of this skycell in the loaded skymap
`length`
`name`	name of this skycell, for instance `315p86x50y75`
`orientation`
`pixel_scale`	degrees per pixel
`pixel_shape`	number of pixels across
`polygon`	spherical polygon representing this skycell
`projection_region`	Projection region containing this skycell.
`radec_center`	center point in right ascension and declination
`radec_corners`	corners in right ascension and declination in the order given by the loaded skymap
`vectorpoint_center`	center in 3D Cartesian space on the unit sphere
`vectorpoint_corners`	corners in 3D Cartesian space on the unit sphere
`wcs`	WCS representing this skycell
`wcs_info`	WCS properties as defined in the Level 3 association schema
`xy_tangent`	center point in pixel coordinates

Methods Summary

`from_asn`(asn[, skymap])	retrieve a skycell from WCS info or a target specified in an association
`from_data`(data[, skymap])	build an index-less skycell instance from a data array
`from_name`(name[, skymap])	Retrieve a sky cell from the sky map [skymap] by its name.

Attributes Documentation

area = 1.7760288493318122e-06

data

Skycell data.

(“name”, “ra_center”, “dec_center”, “orientat”, “x_tangent”, “y_tangent”, “ra_corn1”, “dec_corn1”, “ra_corn2”, “dec_corn2”, “ra_corn3”, “dec_corn3”, “ra_corn4”, “dec_corn4”)

index: index of this skycell in the loaded skymap

length = 0.107984

name: name of this skycell, for instance 315p86x50y75

Note

the name of a skycell center comprises the rounded center coordinates of its containing projection region in right ascension and declination, and the XY location of the skycell within its projection region in units of ordinal skycells from that center

orientation

pixel_scale: degrees per pixel

pixel_shape: number of pixels across

polygon[source]: spherical polygon representing this skycell

projection_region[source]: Projection region containing this skycell.

radec_center: center point in right ascension and declination

radec_corners: corners in right ascension and declination in the order given by the loaded skymap

vectorpoint_center[source]: center in 3D Cartesian space on the unit sphere

vectorpoint_corners[source]: corners in 3D Cartesian space on the unit sphere

wcs[source]: WCS representing this skycell

wcs_info: WCS properties as defined in the Level 3 association schema

xy_tangent: center point in pixel coordinates

Methods Documentation

classmethod from_asn(asn: dict | str, skymap: SkyMap = None) → SkyCell[source]

retrieve a skycell from WCS info or a target specified in an association

Attempts to find a skycell name from the following in order:

skycell_wcs_info.name
target

Parameters:

asn (dict | str) – association dictionary or a path to an association file to load
skymap (SkyMap) – sky map instance; defaults to global SKYMAP (Default value = None)

classmethod from_data(data: void, skymap: SkyMap = None) → SkyCell[source]

build an index-less skycell instance from a data array

Parameters:

data (np.void) – array with skycell parameters (see schema)
skymap (SkyMap) – sky map instancel; defaults to global SKYMAP (Default value = None)

classmethod from_name(name: str, skymap: SkyMap = None) → SkyCell[source]

Retrieve a sky cell from the sky map [skymap] by its name.

Parameters:

name (str) – Name of a skycell, for instance 315p86x50y75.
skymap (SkyMap) – sky map instance; defaults to global SKYMAP (Default value = None)