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AlignTimeScale - Time scale to use when aligning TimeFrames

Description:
This attribute controls how a TimeFrame behaves when it is used (by AST_FINDFRAME or AST_CONVERT) as a template to match another (target) TimeFrame. It identifies the time scale in which alignment is to occur. See the TimeScale attribute for a desription of the values which may be assigned to this attribute. The default AlignTimeScale value depends on the current value of TimeScale: if TimeScale is UT1, GMST, LMST or LAST, the default for AlignTimeScale is UT1, for all other TimeScales the default is TAI.

When AST_FindFrame or AST_CONVERT is used on two TimeFrames (potentially describing different time coordinate systems), it returns a Mapping which can be used to transform a position in one TimeFrame into the corresponding position in the other. The Mapping is made up of the following steps in the indicated order:

  • Map values from the system used by the target (MJD, JD, etc) to the system specified by the AlignSystem attribute.

  • Map these values from the target's time scale to the time scale specified by the AlignTimeScale attribute.

  • Map these values from the time scale specified by the AlignTimeScale attribute, to the template's time scale.

  • Map these values from the system specified by the AlignSystem attribute, to the system used by the template.
Type:
String.
Class Applicability:
TimeFrame
All TimeFrames have this attribute.


next up previous 264
Next: AllWarnings - A list of all currently available condition names
Up: AST Attribute Descriptions
Previous: AlignSystem - Coordinate system in which to align the Frame

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