SkyOffsetFrame

class astropy.coordinates.SkyOffsetFrame(*args, **kwargs)

Bases: BaseCoordinateFrame

A frame which is relative to some specific position and oriented to match its frame.

SkyOffsetFrames always have component names for spherical coordinates of lon/lat, not the component names for the frame of origin.

This is useful for calculating offsets and dithers in the frame of the sky relative to an arbitrary position. Coordinates in this frame are both centered on the position specified by the origin coordinate, and they are oriented in the same manner as the origin frame. E.g., if origin is ICRS, this object’s lat will be pointed in the direction of Dec, while lon will point in the direction of RA.

For more on skyoffset frames, see “Sky Offset” Frames.

Parameters:

representationBaseRepresentation or python:None

A representation object or None to have no data (or use the other keywords)

originastropy:coordinate-like

The coordinate which specifies the origin of this frame. Note that this origin is used purely for on-sky location/rotation. It can have a distance but it will not be used by this SkyOffsetFrame.

rotationastropy:angle-like

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.

Notes

SkyOffsetFrame is a factory class. That is, the objects that it yields are not actually objects of class SkyOffsetFrame. Instead, distinct classes are created on-the-fly for whatever the frame class is of origin.

Attributes Summary

default_differential	Default representation for differential data (e.g., velocity)
default_representation	Default representation for position data
frame_attributes
frame_specific_representation_info	Mapping for frame-specific component names
name
origin	The origin of the offset frame
rotation	The rotation angle for the frame orientation

Methods Summary

represent_as(base[, s, in_frame_units])

Ensure the wrap angle for any spherical representations.

Attributes Documentation

default_differential

Default representation for differential data (e.g., velocity)

default_representation

Default representation for position data

frame_attributes = {'origin': <astropy.coordinates.attributes.CoordinateAttribute object>, 'rotation': <astropy.coordinates.attributes.QuantityAttribute object>}

frame_specific_representation_info

Mapping for frame-specific component names

name = 'skyoffsetframe'

origin

The origin of the offset frame

No default value

rotation

The rotation angle for the frame orientation

Default: 0.0 deg

Methods Documentation

represent_as(base, s='base', in_frame_units=False)

Ensure the wrap angle for any spherical representations.