[evlatests] Time stamps: BDF vs. SDM vs. CASA & AIPS

[Keith Cummings]

David Harland wrote:
> On Fri, June 24, 2011 12:51 pm, Michael Rupen wrote:
>   
>> ...
>>
>> * SDM Tables take their times from observation documents which give
>>    the requested scan start times.  The OPT produces scans in LST,
>>    which unless you work hard are aligned on LST seconds.
>>     
>
> An amplification here for those less familiar w/ the OPT, and a question
> regarding how the OST (dynamic scheduler) is used in practice:
>
> The OPT allows users to choose from one of 6 types of timings for a scan. 
> Two axes:
>   1. Time definition: UT vs LST
>   2. Time type: scan-stop, on-source, total-duration
>
> In order for all OPT scans to be aligned on integral LST seconds we'd need
> to have all scans expressed as LST total-duration (which is, at least
> currently, the norm) AND we'd need the model-to-script (m2s) algorithm to
> be fed a start time that was an LST w/ no fractional seconds.
>
> Question (for Keith): are the start times that the OST feeds to m2s
> necessarily LSTs w/ no fractional seconds?
>   
The OST does NOT schedule SBs to run on whole second intervals; 
fractional seconds are usually included.
Some rounding to the next whole second logic was recently added, but 
this does not cover every case.
-Keith
> Even if the above is answered in the affirmative, as we build the script
> we're continually converting away from LST to UT in order to put scan
> start MJDs in the script.  I'd be quite surprised if we didn't accumulate
> rounding error of at least fractions of a millisecond, and possibly more. 
> UT is the native time type for most, if not all, of our group's code.  LST
> is a convenience provided for the users.
>
>
>   
>>    ..the requested scan interval will not in general contain an
>>    integral number of 1sec UT integrations aligned on UT seconds...
>>     
>
> I've had a chat w/ more than one person about forcing scans to be integral
> multiples of integration times.  Nothing has been settled in this area
> yet.
>   
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