[evla-sw-discuss] Keeping track of spectral windows at the EVLA: SDM vs. BDF

[Vrcic, Sonja]

Of course this begs the question of who comes up with swbbName and swIndex
to begin with.  This seems properly left to the OPT: there is enough
information there, and these values can be determined independently for
every scan.  It would be preferable to have a deterministic algorithm for
doing so.  For swbbName this is trivial.  For swIndex within a given
swbbName I propose:

   1- sort by the lower edge of the lowest frequency channel in each subband
     (to match the ALMA ACA correlator)
   2- for remaining matches, give the lower swIndex to the SpW with
     the narrower channels
   3- for remaining matches, give the lower swIndex to the SpW with the
     fewer total channels
   4- at this stage we have only exact matches left.  If the OPT or whatever
     is explicitly setting the StB filter to be used, the lower filter gets
     the lower swIndex.



Proposed new attributes convey important information; it seems to me that it is better
to define two new VCI attributes (swbbName and swIndex). 
Using VCI "name" for this purpose will look as a cludge; at this early stage we can add things to schema without worrying about legacy code.
Adding a new attribute to VCI schema is not a big deal; most of the work is in implementing the functionality. 


Comment regarding selection of swIndex step 4:
OPT assigns the Subband ID (SBID). 
The CM uses the filter with the same ID as subband, if possible. 
If not possible, CM uses the first available (i.e. unused) filter).
I propose that the swIndex in step 4 should be assignd according to the SBID (most of the time that would be the same as Filter ID).


Should I then add the following:
swbbName to element baseband, type:string (in fact enumeration)
swIndex to element subband, type:int.


Sonja 






All of this of course is negotiable.

A couple points:

* In the BDFs, all SpW in "lower" swbbName's come before all SpW in "higher"
   swbbName's, regardless of the actual frequency tunings.  A/C comes
   before B/D, full stop; similarly data from A1/C1_3BIT comes before
   A/C_8BIT.

* In the BDFs, within a given swbbName, the above scheme would put
   non-overlapping SpW in frequency order (low to high).

* None of this says ANYTHING about the ordering of the actual Spectral
   Windows seen by the observer in post-processing, or even in the SDM.
   That is a separate discussion, which I hope to initiate tomorrow or
   Thursday.



Comments?

            Michael

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listmgr.nrao.edu/pipermail/evla-sw-discuss/attachments/20100217/8be41d1e/attachment.html>