This attribute
identifies the rest frame in which the source velocity or redshift is stored (the source velocity or
redshift is accessed using attribute
SourceVel). When setting a new value for the SourceVel attribute,
the source velocity or redshift should be supplied in the rest frame indicated by this attribute.
Likewise, when getting the value of the SourceVel attribute, the velocity or redshift will be returned in
this rest frame.
If the value of SourceVRF is changed, the value stored for SourceVel will be converted from the old to
the new rest frame.
The values which can be supplied are the same as for the StdOfRest attribute (except that SourceVRF
cannot be set to " Source" ). The default value is " Helio" .