This attribute controls how a SpecFrame behaves when it is used (by
AST_FINDFRAME or AST_CONVERT) as a template to match another (target)
SpecFrame. It identifies the standard of rest in which alignment is
to occur. See the StdOfRest attribute for a desription of the values
which may be assigned to this attribute. The default AlignStdOfRest
value is "Helio" (heliographic).
When AST_FindFrame or AST_CONVERT is used on two SpecFrames (potentially
describing different spectral coordinate systems), it returns a Mapping
which can be used to transform a position in one SpecFrame 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 (wavelength,
apparent radial velocity, etc) to the system specified by the
AlignSystem attribute, using the target's rest frequency if necessary.
- Map these values from the target's standard of rest to the standard of
rest specified by the AlignStdOfRest attribute, using the Epoch, ObsLat,
ObsLon, ObsAlt, RefDec and RefRA attributes of the target to define the
two standards of rest.
- Map these values from the standard of rest specified by the
AlignStdOfRest attribute, to the template's standard of rest, using the
Epoch, ObsLat, ObsLon, ObsAlt, RefDec and RefRA attributes of the
template to define the two standards of rest.
- Map these values from the system specified by the AlignSystem
attribute, to the system used by the template, using the template's
rest frequency if necessary.