#### Description:

This attribute controls how a Frame behaves when it is used (by astFindFrame or astConvert) as a template to match another (target) Frame. It identifies the coordinate system in which the two Frames will be aligned by the match.

The values which may be assigned to this attribute, and its default value, depend on the class of Frame and are described in the `"` Applicability`"` section below. In general, the AlignSystem attribute will accept any of the values which may be assigned to the System attribute.

The Mapping returned by AST_FINDFRAME or AST_CONVERT will use the coordinate system specified by the AlignSystem attribute as an intermediate coordinate system. The total returned Mapping will first map positions from the first Frame into this intermediate coordinate system, using the attributes of the first Frame. It will then map these positions from the intermediate coordinate system into the second Frame, using the attributes of the second Frame.

Type:

  String.

#### Applicability

##### Frame

The AlignSystem attribute for a basic Frame always equals `"` Cartesian`"` , and may not be altered.

##### CmpFrame

The AlignSystem attribute for a CmpFrame always equals `"` Compound`"` , and may not be altered.

##### FrameSet

The AlignSystem attribute of a FrameSet is the same as that of its current Frame (as specified by the Current attribute).

##### SkyFrame

The default AlignSystem attribute for a SkyFrame is `"` ICRS`"` .

##### SpecFrame

The default AlignSystem attribute for a SpecFrame is `"` Wave`"` (wavelength).

##### TimeFrame

The default AlignSystem attribute for a TimeFrame is `"` MJD`"` .
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