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SkyFrame - Celestial coordinate system description

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.

Constructor Function:
AST_SKYFRAME
Inheritance
The SkyFrame class inherits from the Frame class.
Attributes
In addition to those attributes common to all Frames, every SkyFrame also has the following attributes:

  • AlignOffset: Align SkyFrames using the offset coordinate system?

  • AsTime(axis): Format celestial coordinates as times?

  • Equinox: Epoch of the mean equinox

  • IsLatAxis: Is the specified axis the latitude axis?

  • IsLonAxis: Is the specified axis the longitude axis?

  • LatAxis: Index of the latitude axis

  • LonAxis: Index of the longitude axis

  • NegLon: Display longitude values in the range [-pi,pi]?

  • Projection: Sky projection description.

  • SkyRef: Position defining location of the offset coordinate system

  • SkyRefIs: Selects the nature of the offset coordinate system

  • SkyRefP: Position defining orientation of the offset coordinate system
Functions
In addition to those routines applicable to all Frames, the following routines may also be applied to all SkyFrames:



next up previous 264
Next: SlaMap - Sequence of celestial coordinate conversions
Up: AST Class Descriptions
Previous: SkyAxis - Store celestial axis information

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council