This attribute controls how a TimeFrame behaves when it is used (by astFindFrame or astConvert) 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 astFindFrame or astConvert 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.

TimeFrame