#### Description:

This attribute controls how a DSBSpecFrame behaves when an attempt is made to align it with another DSBSpecFrame using astFindFrame or astConvert. If both DSBSpecFrames have a non-zero value for AlignSideBand, the value of the SideBand attribute in each DSBSpecFrame is used so that alignment occurs between sidebands. That is, if one DSBSpecFrame represents USB and the other represents LSB then astFindFrame and astConvert will recognise that the DSBSpecFrames represent different sidebands and will take this into account when constructing the Mapping that maps positions in one DSBSpecFrame into the other. If AlignSideBand in either DSBSpecFrame is set to zero, then the values of the SideBand attributes are ignored. In the above example, this would result in a frequency in the first DSBSpecFrame being mapped onto the same frequency in the second DSBSpecFrame, even though those frequencies refer to different sidebands. In other words, if either AlignSideBand attribute is zero, then the two DSBSpecFrames aligns like basic SpecFrames. The default value for AlignSideBand is zero.

When astFindFrame or astConvert is used on two DSBSpecFrames (potentially describing different spectral coordinate systems and/or sidebands), it returns a Mapping which can be used to transform a position in one DSBSpecFrame into the corresponding position in the other. The Mapping is made up of the following steps in the indicated order:

- If both DSBSpecFrames have a value of 1 for the AlignSideBand attribute, map values from the target`’` s current sideband (given by its SideBand attribute) to the observed sideband (whether USB or LSB). If the target already represents the observed sideband, this step will leave the values unchanged. If either of the two DSBSpecFrames have a value of zero for its AlignSideBand attribute, then this step is omitted.

- Map the values from the spectral system of the target to the spectral system of the template. This Mapping takes into account all the inherited SpecFrame attributes such as System, StdOfRest, Unit, etc.

- If both DSBSpecFrames have a value of 1 for the AlignSideBand attribute, map values from the result`’` s observed sideband to the result`’` s current sideband (given by its SideBand attribute). If the result already represents the observed sideband, this step will leave the values unchanged. If either of the two DSBSpecFrames have a value of zero for its AlignSideBand attribute, then this step is omitted.

Type:

  Integer (boolean).

#### Applicability

##### DSBSpecFrame

All DSBSpecFrames have this attribute.
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