Celestial coordinate system description


A SkyFrame is a specialised form of Frame which describes celestial longitude/latitude coordinate systems. The particular celestial coordinate system to be represented is specified by setting the SkyFrame s System attribute (currently, the default is ICRS) qualified, as necessary, by a mean Equinox value and/or an Epoch.

For each of the supported celestial coordinate systems, a SkyFrame can apply an optional shift of origin to create a coordinate system representing offsets within the celestial coordinate system from some specified reference point. This offset coordinate system can also be rotated to define new longitude and latitude axes. See attributes SkyRef, SkyRefIs, SkyRefP and AlignOffset.

All the coordinate values used by a SkyFrame are in radians. These may be formatted in more conventional ways for display by using AST_FORMAT. For a SkyFrame, the Unit attribute describes the formatted value of a SkyFrame axis, and may for instance be " h:m:s" , indicating that a formatted axis value contains colon-separated fields for hours, minutes and seconds. On the other hand, the InternalUnit attribute for a SkyFrame is always set to " rad" (i.e. radians), indicating that the unformatted (i.e. floating point) axis values used by application code are always in units of radians

Constructor Function



The SkyFrame class inherits from the Frame class.


In addition to those attributes common to all Frames, every SkyFrame also has the following attributes:


In addition to those routines applicable to all Frames, the following routines may also be applied to all SkyFrames: