SkyCoord¶
-
class
astropy.coordinates.
SkyCoord
(*args, copy=True, **kwargs)[source] [edit on github]¶ Bases:
astropy.utils.misc.ShapedLikeNDArray
High-level object providing a flexible interface for celestial coordinate representation, manipulation, and transformation between systems.
The
SkyCoord
class accepts a wide variety of inputs for initialization. At a minimum these must provide one or more celestial coordinate values with unambiguous units. Inputs may be scalars or lists/tuples/arrays, yielding scalar or array coordinates (can be checked viaSkyCoord.isscalar
). Typically one also specifies the coordinate frame, though this is not required. The general pattern for spherical representations is:SkyCoord(COORD, [FRAME], keyword_args ...) SkyCoord(LON, LAT, [FRAME], keyword_args ...) SkyCoord(LON, LAT, [DISTANCE], frame=FRAME, unit=UNIT, keyword_args ...) SkyCoord([FRAME], <lon_attr>=LON, <lat_attr>=LAT, keyword_args ...)
It is also possible to input coordinate values in other representations such as cartesian or cylindrical. In this case one includes the keyword argument
representation_type='cartesian'
(for example) along with data inx
,y
, andz
.See also: http://docs.astropy.org/en/stable/coordinates/
Parameters: - frame :
BaseCoordinateFrame
class or string, optional Type of coordinate frame this
SkyCoord
should represent. Defaults to to ICRS if not given or given as None.- unit :
Unit
, string, or tuple ofUnit
or str, optional Units for supplied
LON
andLAT
values, respectively. If only one unit is supplied then it applies to bothLON
andLAT
.- obstime : valid
Time
initializer, optional Time of observation
- equinox : valid
Time
initializer, optional Coordinate frame equinox
- representation_type : str or Representation class
Specifies the representation, e.g. ‘spherical’, ‘cartesian’, or ‘cylindrical’. This affects the positional args and other keyword args which must correspond to the given representation.
- copy : bool, optional
If
True
(default), a copy of any coordinate data is made. This argument can only be passed in as a keyword argument.- **keyword_args
Other keyword arguments as applicable for user-defined coordinate frames. Common options include:
- ra, dec : valid
Angle
initializer, optional RA and Dec for frames where
ra
anddec
are keys in the frame’srepresentation_component_names
, includingICRS
,FK5
,FK4
, andFK4NoETerms
.- pm_ra_cosdec, pm_dec :
Quantity
, optional Proper motion components, in angle per time units.
- l, b : valid
Angle
initializer, optional Galactic
l
andb
for for frames wherel
andb
are keys in the frame’srepresentation_component_names
, including theGalactic
frame.- pm_l_cosb, pm_b :
Quantity
, optional Proper motion components in the
Galactic
frame, in angle per time units.- x, y, z : float or
Quantity
, optional Cartesian coordinates values
- u, v, w : float or
Quantity
, optional Cartesian coordinates values for the Galactic frame.
- radial_velocity :
Quantity
, optional The component of the velocity along the line-of-sight (i.e., the radial direction), in velocity units.
- ra, dec : valid
Examples
The examples below illustrate common ways of initializing a
SkyCoord
object. For a complete description of the allowed syntax see the full coordinates documentation. First some imports:>>> from astropy.coordinates import SkyCoord # High-level coordinates >>> from astropy.coordinates import ICRS, Galactic, FK4, FK5 # Low-level frames >>> from astropy.coordinates import Angle, Latitude, Longitude # Angles >>> import astropy.units as u
The coordinate values and frame specification can now be provided using positional and keyword arguments:
>>> c = SkyCoord(10, 20, unit="deg") # defaults to ICRS frame >>> c = SkyCoord([1, 2, 3], [-30, 45, 8], frame="icrs", unit="deg") # 3 coords >>> coords = ["1:12:43.2 +1:12:43", "1 12 43.2 +1 12 43"] >>> c = SkyCoord(coords, frame=FK4, unit=(u.deg, u.hourangle), obstime="J1992.21") >>> c = SkyCoord("1h12m43.2s +1d12m43s", frame=Galactic) # Units from string >>> c = SkyCoord(frame="galactic", l="1h12m43.2s", b="+1d12m43s") >>> ra = Longitude([1, 2, 3], unit=u.deg) # Could also use Angle >>> dec = np.array([4.5, 5.2, 6.3]) * u.deg # Astropy Quantity >>> c = SkyCoord(ra, dec, frame='icrs') >>> c = SkyCoord(frame=ICRS, ra=ra, dec=dec, obstime='2001-01-02T12:34:56') >>> c = FK4(1 * u.deg, 2 * u.deg) # Uses defaults for obstime, equinox >>> c = SkyCoord(c, obstime='J2010.11', equinox='B1965') # Override defaults >>> c = SkyCoord(w=0, u=1, v=2, unit='kpc', frame='galactic', ... representation_type='cartesian') >>> c = SkyCoord([ICRS(ra=1*u.deg, dec=2*u.deg), ICRS(ra=3*u.deg, dec=4*u.deg)])
Velocity components (proper motions or radial velocities) can also be provided in a similar manner:
>>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, radial_velocity=10*u.km/u.s) >>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, pm_ra_cosdec=2*u.mas/u.yr, pm_dec=1*u.mas/u.yr)
As shown, the frame can be a
BaseCoordinateFrame
class or the corresponding string alias. The frame classes that are built in to astropy areICRS
,FK5
,FK4
,FK4NoETerms
, andGalactic
. The string aliases are simply lower-case versions of the class name, and allow for creating aSkyCoord
object and transforming frames without explicitly importing the frame classes.Attributes Summary
frame
info
Container for meta information like name, description, format. representation
representation_type
shape
The shape of the instance and underlying arrays. Methods Summary
apply_space_motion
([new_obstime, dt])Compute the position of the source represented by this coordinate object to a new time using the velocities stored in this object and assuming linear space motion (including relativistic corrections). contained_by
(wcs[, image])Determines if the SkyCoord is contained in the given wcs footprint. directional_offset_by
(position_angle, separation)Computes coordinates at the given offset from this coordinate. from_name
(name[, frame, parse])Given a name, query the CDS name resolver to attempt to retrieve coordinate information for that object. from_pixel
(xp, yp, wcs[, origin, mode])Create a new SkyCoord
from pixel coordinates using anWCS
object.get_constellation
([short_name, …])Determines the constellation(s) of the coordinates this SkyCoord
contains.guess_from_table
(table, **coord_kwargs)A convenience method to create and return a new SkyCoord
from the data in an astropy Table.is_equivalent_frame
(other)Checks if this object’s frame as the same as that of the other
object.match_to_catalog_3d
(catalogcoord[, nthneighbor])Finds the nearest 3-dimensional matches of this coordinate to a set of catalog coordinates. match_to_catalog_sky
(catalogcoord[, nthneighbor])Finds the nearest on-sky matches of this coordinate in a set of catalog coordinates. position_angle
(other)Computes the on-sky position angle (East of North) between this SkyCoord
and another.radial_velocity_correction
([kind, obstime, …])Compute the correction required to convert a radial velocity at a given time and place on the Earth’s Surface to a barycentric or heliocentric velocity. search_around_3d
(searcharoundcoords, distlimit)Searches for all coordinates in this object around a supplied set of points within a given 3D radius. search_around_sky
(searcharoundcoords, seplimit)Searches for all coordinates in this object around a supplied set of points within a given on-sky separation. separation
(other)Computes on-sky separation between this coordinate and another. separation_3d
(other)Computes three dimensional separation between this coordinate and another. skyoffset_frame
([rotation])Returns the sky offset frame with this SkyCoord
at the origin.spherical_offsets_to
(tocoord)Computes angular offsets to go from this coordinate to another. to_pixel
(wcs[, origin, mode])Convert this coordinate to pixel coordinates using a WCS
object.to_string
([style])A string representation of the coordinates. transform_to
(frame[, merge_attributes])Transform this coordinate to a new frame. Attributes Documentation
-
frame
¶
-
info
¶ Container for meta information like name, description, format. This is required when the object is used as a mixin column within a table, but can be used as a general way to store meta information.
-
representation
¶
-
representation_type
¶
-
shape
¶ The shape of the instance and underlying arrays.
Methods Documentation
-
apply_space_motion
(new_obstime=None, dt=None)[source] [edit on github]¶ Compute the position of the source represented by this coordinate object to a new time using the velocities stored in this object and assuming linear space motion (including relativistic corrections). This is sometimes referred to as an “epoch transformation.”
The initial time before the evolution is taken from the
obstime
attribute of this coordinate. Note that this method currently does not support evolving coordinates where the frame has anobstime
frame attribute, so theobstime
is only used for storing the before and after times, not actually as an attribute of the frame. Alternatively, ifdt
is given, anobstime
need not be provided at all.Parameters: Returns: - new_coord :
SkyCoord
A new coordinate object with the evolved location of this coordinate at the new time.
obstime
will be set on this object to the new time only ifself
also hasobstime
.
- new_coord :
-
contained_by
(wcs, image=None, **kwargs)[source] [edit on github]¶ Determines if the SkyCoord is contained in the given wcs footprint.
Parameters: - wcs :
WCS
The coordinate to check if it is within the wcs coordinate.
- image : array
Optional. The image associated with the wcs object that the cooordinate is being checked against. If not given the naxis keywords will be used to determine if the coordinate falls within the wcs footprint.
- **kwargs :
Additional arguments to pass to
to_pixel
Returns: - response : bool
True means the WCS footprint contains the coordinate, False means it does not.
- wcs :
-
directional_offset_by
(position_angle, separation)[source] [edit on github]¶ Computes coordinates at the given offset from this coordinate.
Parameters: Returns: - newpoints :
SkyCoord
The coordinates for the location that corresponds to offsetting by the given
position_angle
andseparation
.
See also
position_angle
- inverse operation for the
position_angle
component separation
- inverse operation for the
separation
component
Notes
Returned SkyCoord frame retains only the frame attributes that are for the resulting frame type. (e.g. if the input frame is
ICRS
, anequinox
value will be retained, but anobstime
will not.)For a more complete set of transform offsets, use
WCS
.skyoffset_frame()
can also be used to create a spherical frame with (lat=0, lon=0) at a reference point, approximating an xy cartesian system for small offsets. This method is distinct in that it is accurate on the sphere.- newpoints :
-
classmethod
from_name
(name, frame='icrs', parse=False)[source] [edit on github]¶ Given a name, query the CDS name resolver to attempt to retrieve coordinate information for that object. The search database, sesame url, and query timeout can be set through configuration items in
astropy.coordinates.name_resolve
– see docstring forget_icrs_coordinates
for more information.Parameters: - name : str
The name of the object to get coordinates for, e.g.
'M42'
.- frame : str or
BaseCoordinateFrame
class or instance The frame to transform the object to.
- parse: bool
Whether to attempt extracting the coordinates from the name by parsing with a regex. For objects catalog names that have J-coordinates embedded in their names eg: ‘CRTS SSS100805 J194428-420209’, this may be much faster than a sesame query for the same object name. The coordinates extracted in this way may differ from the database coordinates by a few deci-arcseconds, so only use this option if you do not need sub-arcsecond accuracy for coordinates.
Returns: - coord : SkyCoord
Instance of the SkyCoord class.
-
classmethod
from_pixel
(xp, yp, wcs, origin=0, mode='all')[source] [edit on github]¶ Create a new
SkyCoord
from pixel coordinates using anWCS
object.Parameters: - xp, yp : float or
numpy.ndarray
The coordinates to convert.
- wcs :
WCS
The WCS to use for convert
- origin : int
Whether to return 0 or 1-based pixel coordinates.
- mode : ‘all’ or ‘wcs’
Whether to do the transformation including distortions (
'all'
) or only including only the core WCS transformation ('wcs'
).
Returns: - coord : an instance of this class
A new object with sky coordinates corresponding to the input
xp
andyp
.
See also
to_pixel
- to do the inverse operation
astropy.wcs.utils.pixel_to_skycoord
- the implementation of this method
- xp, yp : float or
-
get_constellation
(short_name=False, constellation_list='iau')[source] [edit on github]¶ Determines the constellation(s) of the coordinates this
SkyCoord
contains.Parameters: - short_name : bool
If True, the returned names are the IAU-sanctioned abbreviated names. Otherwise, full names for the constellations are used.
- constellation_list : str
The set of constellations to use. Currently only
'iau'
is supported, meaning the 88 “modern” constellations endorsed by the IAU.
Returns: - constellation : str or string array
If this is a scalar coordinate, returns the name of the constellation. If it is an array
SkyCoord
, it returns an array of names.
Notes
To determine which constellation a point on the sky is in, this first precesses to B1875, and then uses the Delporte boundaries of the 88 modern constellations, as tabulated by Roman 1987.
-
classmethod
guess_from_table
(table, **coord_kwargs)[source] [edit on github]¶ A convenience method to create and return a new
SkyCoord
from the data in an astropy Table.This method matches table columns that start with the case-insensitive names of the the components of the requested frames, if they are also followed by a non-alphanumeric character. It will also match columns that end with the component name if a non-alphanumeric character is before it.
For example, the first rule means columns with names like
'RA[J2000]'
or'ra'
will be interpreted asra
attributes forICRS
frames, but'RAJ2000'
or'radius'
are not. Similarly, the second rule applied to theGalactic
frame means that a column named'gal_l'
will be used as the thel
component, butgall
or'fill'
will not.The definition of alphanumeric here is based on Unicode’s definition of alphanumeric, except without
_
(which is normally considered alphanumeric). So for ASCII, this means the non-alphanumeric characters are<space>_!"#$%&'()*+,-./\:;<=>?@[]^`{|}~
).Parameters: - table : astropy.Table
The table to load data from.
- coord_kwargs
Any additional keyword arguments are passed directly to this class’s constructor.
Returns: - newsc : same as this class
The new
SkyCoord
(or subclass) object.
-
is_equivalent_frame
(other)[source] [edit on github]¶ Checks if this object’s frame as the same as that of the
other
object.To be the same frame, two objects must be the same frame class and have the same frame attributes. For two
SkyCoord
objects, all of the frame attributes have to match, not just those relevant for the object’s frame.Parameters: - other : SkyCoord or BaseCoordinateFrame
The other object to check.
Returns: - isequiv : bool
True if the frames are the same, False if not.
Raises: - TypeError
If
other
isn’t aSkyCoord
or aBaseCoordinateFrame
or subclass.
-
match_to_catalog_3d
(catalogcoord, nthneighbor=1)[source] [edit on github]¶ Finds the nearest 3-dimensional matches of this coordinate to a set of catalog coordinates.
This finds the 3-dimensional closest neighbor, which is only different from the on-sky distance if
distance
is set in this object or thecatalogcoord
object.For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - catalogcoord :
SkyCoord
orBaseCoordinateFrame
The base catalog in which to search for matches. Typically this will be a coordinate object that is an array (i.e.,
catalogcoord.isscalar == False
)- nthneighbor : int, optional
Which closest neighbor to search for. Typically
1
is desired here, as that is correct for matching one set of coordinates to another. The next likely use case is2
, for matching a coordinate catalog against itself (1
is inappropriate because each point will find itself as the closest match).
Returns: - idx : integer array
Indices into
catalogcoord
to get the matched points for each of this object’s coordinates. Shape matches this object.- sep2d :
Angle
The on-sky separation between the closest match for each element in this object in
catalogcoord
. Shape matches this object.- dist3d :
Quantity
The 3D distance between the closest match for each element in this object in
catalogcoord
. Shape matches this object.
Notes
This method requires SciPy to be installed or it will fail.
- catalogcoord :
-
match_to_catalog_sky
(catalogcoord, nthneighbor=1)[source] [edit on github]¶ Finds the nearest on-sky matches of this coordinate in a set of catalog coordinates.
For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - catalogcoord :
SkyCoord
orBaseCoordinateFrame
The base catalog in which to search for matches. Typically this will be a coordinate object that is an array (i.e.,
catalogcoord.isscalar == False
)- nthneighbor : int, optional
Which closest neighbor to search for. Typically
1
is desired here, as that is correct for matching one set of coordinates to another. The next likely use case is2
, for matching a coordinate catalog against itself (1
is inappropriate because each point will find itself as the closest match).
Returns: - idx : integer array
Indices into
catalogcoord
to get the matched points for each of this object’s coordinates. Shape matches this object.- sep2d :
Angle
The on-sky separation between the closest match for each element in this object in
catalogcoord
. Shape matches this object.- dist3d :
Quantity
The 3D distance between the closest match for each element in this object in
catalogcoord
. Shape matches this object. Unless both this andcatalogcoord
have associated distances, this quantity assumes that all sources are at a distance of 1 (dimensionless).
Notes
This method requires SciPy to be installed or it will fail.
- catalogcoord :
-
position_angle
(other)[source] [edit on github]¶ Computes the on-sky position angle (East of North) between this
SkyCoord
and another.Parameters: - other :
SkyCoord
The other coordinate to compute the position angle to. It is treated as the “head” of the vector of the position angle.
Returns: Examples
>>> c1 = SkyCoord(0*u.deg, 0*u.deg) >>> c2 = SkyCoord(1*u.deg, 0*u.deg) >>> c1.position_angle(c2).degree 90.0 >>> c3 = SkyCoord(1*u.deg, 1*u.deg) >>> c1.position_angle(c3).degree # doctest: +FLOAT_CMP 44.995636455344844
- other :
-
radial_velocity_correction
(kind='barycentric', obstime=None, location=None)[source] [edit on github]¶ Compute the correction required to convert a radial velocity at a given time and place on the Earth’s Surface to a barycentric or heliocentric velocity.
Parameters: - kind : str
The kind of velocity correction. Must be ‘barycentric’ or ‘heliocentric’.
- obstime :
Time
or None, optional The time at which to compute the correction. If
None
, theobstime
frame attribute on theSkyCoord
will be used.- location :
EarthLocation
or None, optional The observer location at which to compute the correction. If
None
, thelocation
frame attribute on the passed-inobstime
will be used, and if that is None, thelocation
frame attribute on theSkyCoord
will be used.
Returns: - vcorr :
Quantity
with velocity units The correction with a positive sign. I.e., add this to an observed radial velocity to get the barycentric (or heliocentric) velocity. If m/s precision or better is needed, see the notes below.
Raises: - ValueError
If either
obstime
orlocation
are passed in (notNone
) when the frame attribute is already set on thisSkyCoord
.- TypeError
If
obstime
orlocation
aren’t provided, either as arguments or as frame attributes.
Notes
The barycentric correction is calculated to higher precision than the heliocentric correction and includes additional physics (e.g time dilation). Use barycentric corrections if m/s precision is required.
The algorithm here is sufficient to perform corrections at the mm/s level, but care is needed in application. Strictly speaking, the barycentric correction is multiplicative and should be applied as:
sc = SkyCoord(1*u.deg, 2*u.deg) vcorr = sc.rv_correction(kind='barycentric', obstime=t, location=loc) rv = rv + vcorr + rv * vcorr / consts.c
If your target is nearby and/or has finite proper motion you may need to account for terms arising from this. See Wright & Eastmann (2014) for details.
The default is for this method to use the builtin ephemeris for computing the sun and earth location. Other ephemerides can be chosen by setting the
solar_system_ephemeris
variable, either directly or viawith
statement. For example, to use the JPL ephemeris, do:sc = SkyCoord(1*u.deg, 2*u.deg) with coord.solar_system_ephemeris.set('jpl'): rv += sc.rv_correction(obstime=t, location=loc)
-
search_around_3d
(searcharoundcoords, distlimit)[source] [edit on github]¶ Searches for all coordinates in this object around a supplied set of points within a given 3D radius.
This is intended for use on
SkyCoord
objects with coordinate arrays, rather than a scalar coordinate. For a scalar coordinate, it is better to useseparation_3d
.For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - searcharoundcoords :
SkyCoord
orBaseCoordinateFrame
The coordinates to search around to try to find matching points in this
SkyCoord
. This should be an object with array coordinates, not a scalar coordinate object.- distlimit :
Quantity
with distance units The physical radius to search within.
Returns: - idxsearcharound : integer array
Indices into
self
that matches to the corresponding element ofidxself
. Shape matchesidxself
.- idxself : integer array
Indices into
searcharoundcoords
that matches to the corresponding element ofidxsearcharound
. Shape matchesidxsearcharound
.- sep2d :
Angle
The on-sky separation between the coordinates. Shape matches
idxsearcharound
andidxself
.- dist3d :
Quantity
The 3D distance between the coordinates. Shape matches
idxsearcharound
andidxself
.
Notes
This method requires SciPy (>=0.12.0) to be installed or it will fail.
In the current implementation, the return values are always sorted in the same order as the
searcharoundcoords
(soidxsearcharound
is in ascending order). This is considered an implementation detail, though, so it could change in a future release.- searcharoundcoords :
-
search_around_sky
(searcharoundcoords, seplimit)[source] [edit on github]¶ Searches for all coordinates in this object around a supplied set of points within a given on-sky separation.
This is intended for use on
SkyCoord
objects with coordinate arrays, rather than a scalar coordinate. For a scalar coordinate, it is better to useseparation
.For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - searcharoundcoords :
SkyCoord
orBaseCoordinateFrame
The coordinates to search around to try to find matching points in this
SkyCoord
. This should be an object with array coordinates, not a scalar coordinate object.- seplimit :
Quantity
with angle units The on-sky separation to search within.
Returns: - idxsearcharound : integer array
Indices into
self
that matches to the corresponding element ofidxself
. Shape matchesidxself
.- idxself : integer array
Indices into
searcharoundcoords
that matches to the corresponding element ofidxsearcharound
. Shape matchesidxsearcharound
.- sep2d :
Angle
The on-sky separation between the coordinates. Shape matches
idxsearcharound
andidxself
.- dist3d :
Quantity
The 3D distance between the coordinates. Shape matches
idxsearcharound
andidxself
.
Notes
This method requires SciPy (>=0.12.0) to be installed or it will fail.
In the current implementation, the return values are always sorted in the same order as the
searcharoundcoords
(soidxsearcharound
is in ascending order). This is considered an implementation detail, though, so it could change in a future release.- searcharoundcoords :
-
separation
(other)[source] [edit on github]¶ Computes on-sky separation between this coordinate and another.
Note
If the
other
coordinate object is in a different frame, it is first transformed to the frame of this object. This can lead to unintuitive behavior if not accounted for. Particularly of note is thatself.separation(other)
andother.separation(self)
may not give the same answer in this case.For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - other :
SkyCoord
orBaseCoordinateFrame
The coordinate to get the separation to.
Returns: - sep :
Angle
The on-sky separation between this and the
other
coordinate.
Notes
The separation is calculated using the Vincenty formula, which is stable at all locations, including poles and antipodes [1].
[1] https://en.wikipedia.org/wiki/Great-circle_distance - other :
-
separation_3d
(other)[source] [edit on github]¶ Computes three dimensional separation between this coordinate and another.
For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.
Parameters: - other :
SkyCoord
orBaseCoordinateFrame
The coordinate to get the separation to.
Returns: - sep :
Distance
The real-space distance between these two coordinates.
Raises: - ValueError
If this or the other coordinate do not have distances.
- other :
-
skyoffset_frame
(rotation=None)[source] [edit on github]¶ Returns the sky offset frame with this
SkyCoord
at the origin.Returns: - astrframe :
SkyOffsetFrame
A sky offset frame of the same type as this
SkyCoord
(e.g., if this object has an ICRS coordinate, the resulting frame is SkyOffsetICRS, with the origin set to this object)- rotation :
Angle
orQuantity
with angle units The final rotation of the frame about the
origin
. The sign of the rotation is the left-hand rule. That is, an object at a particular position angle in the un-rotated system will be sent to the positive latitude (z) direction in the final frame.
- astrframe :
-
spherical_offsets_to
(tocoord)[source] [edit on github]¶ Computes angular offsets to go from this coordinate to another.
Parameters: - tocoord :
BaseCoordinateFrame
The coordinate to find the offset to.
Returns: Raises: - ValueError
If the
tocoord
is not in the same frame as this one. This is different from the behavior of theseparation
/separation_3d
methods because the offset components depend critically on the specific choice of frame.
See also
separation
- for the total angular offset (not broken out into components).
position_angle
- for the direction of the offset.
Notes
This uses the sky offset frame machinery, and hence will produce a new sky offset frame if one does not already exist for this object’s frame class.
- tocoord :
-
to_pixel
(wcs, origin=0, mode='all')[source] [edit on github]¶ Convert this coordinate to pixel coordinates using a
WCS
object.Parameters: - wcs :
WCS
The WCS to use for convert
- origin : int
Whether to return 0 or 1-based pixel coordinates.
- mode : ‘all’ or ‘wcs’
Whether to do the transformation including distortions (
'all'
) or only including only the core WCS transformation ('wcs'
).
Returns: - xp, yp :
numpy.ndarray
The pixel coordinates
See also
astropy.wcs.utils.skycoord_to_pixel
- the implementation of this method
- wcs :
-
to_string
(style='decimal', **kwargs)[source] [edit on github]¶ A string representation of the coordinates.
The default styles definitions are:
'decimal': 'lat': {'decimal': True, 'unit': "deg"} 'lon': {'decimal': True, 'unit': "deg"} 'dms': 'lat': {'unit': "deg"} 'lon': {'unit': "deg"} 'hmsdms': 'lat': {'alwayssign': True, 'pad': True, 'unit': "deg"} 'lon': {'pad': True, 'unit': "hour"}
See
to_string()
for details and keyword arguments (the two angles forming the coordinates are are bothAngle
instances). Keyword arguments have precedence over the style defaults and are passed toto_string()
.Parameters: - style : {‘hmsdms’, ‘dms’, ‘decimal’}
The formatting specification to use. These encode the three most common ways to represent coordinates. The default is
decimal
.- kwargs
Keyword args passed to
to_string()
.
-
transform_to
(frame, merge_attributes=True)[source] [edit on github]¶ Transform this coordinate to a new frame.
The precise frame transformed to depends on
merge_attributes
. IfFalse
, the destination frame is used exactly as passed in. But this is often not quite what one wants. E.g., suppose one wants to transform an ICRS coordinate that has an obstime attribute to FK4; in this case, one likely would want to use this information. Thus, the default formerge_attributes
isTrue
, in which the precedence is as follows: (1) explicitly set (i.e., non-default) values in the destination frame; (2) explicitly set values in the source; (3) default value in the destination frame.Note that in either case, any explicitly set attributes on the source
SkyCoord
that are not part of the destination frame’s definition are kept (stored on the resultingSkyCoord
), and thus one can round-trip (e.g., from FK4 to ICRS to FK4 without loosing obstime).Parameters: - frame : str,
BaseCoordinateFrame
class or instance, orSkyCoord
instance The frame to transform this coordinate into. If a
SkyCoord
, the underlying frame is extracted, and all other information ignored.- merge_attributes : bool, optional
Whether the default attributes in the destination frame are allowed to be overridden by explicitly set attributes in the source (see note above; default:
True
).
Returns: Raises: - ValueError
If there is no possible transformation route.
- frame : str,
- frame :