This specifies the origin from which all spectral values are measured. The default value (zero) results in the SpecFrame describing absolute spectral values in the system given by the System attribute (e.g. frequency, velocity, etc). If a SpecFrame is to be used to describe offset from some origin, the SpecOrigin attribute should be set to hold the required origin value. The SpecOrigin value stored inside the SpecFrame structure is modified whenever SpecFrame attribute values are changed so that it refers to the original spectral position.

When setting a new value for this attribute, the supplied value is assumed to be in the system, units and standard of rest described by the SpecFrame. Likewise, when getting the value of this attribute, the value is returned in the system, units and standard of rest described by the SpecFrame. If any of these attributes are changed, then any previously stored SpecOrigin value will also be changed so that refers to the new system, units or standard of rest.

SpecFrame