class astropy.coordinates.SkyOffsetFrame(*args, **kwargs)[source]

Bases: astropy.coordinates.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.

representation : BaseRepresentation or None

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

origin : SkyCoord or low-level coordinate object.

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.

rotation : Angle or Quantity 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.


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


Attributes Documentation

frame_attributes = {'origin': <astropy.coordinates.attributes.CoordinateAttribute object at 0x7f3878bc9780>, 'rotation': <astropy.coordinates.attributes.QuantityAttribute object at 0x7f3878bc9748>}
name = 'skyoffsetframe'
origin = None
rotation = <Quantity 0. deg>