[evlatests] your mail (Antenna Wrapping)
Craig Walker
cwalker at nrao.edu
Mon Mar 8 12:21:17 EST 2010
That is my understanding too. But are we sure the OPT will never be
used, such as when weird setups are required or we want to check
schedules? Just because SCHED can write old VLA observe decks certainly
did not mean that those files weren't passed through Observe in many
cases. But also, situations that might make it hard to follow a fixed
schedule might exist in the on-line system common to all schedules.
That was certainly true in the early VLBA days when the on-line system
had a nice wrap optimizer that minimized the time lost to wraps, but
could not be predicted because of variable factors in how it was run at
observe time. Those who really cared - the geodesy community - wanted
predictability over optimization and we eventually reverted to a simple
and predictable algorithm.
Cheers,
Craig
Walter Brisken wrote:
>
> According to the plan that we (Adam and Matthias, mostly) are coding
> to, the EVLA schedule for VLBI will be generated based on the vex file
> and will not use the OPT at all, so this is not relevant here. Please
> correct me if I'm wrong!
>
> -Walter
>
> On Mon, 8 Mar 2010, Craig Walker wrote:
>
>> I'd just like to remind people that it needs to be possible to generate
>> a schedule that will do exactly what is requested in terms of scan
>> times. This is required for VLBI where the schedule needs to be aligned
>> in time with what is being done at other telescopes. With respect to
>> wraps, this means that either the scheduling program knows the algorithm
>> in use well enough to predict its behavior exactly (which is why we use
>> a simple algorithm on the VLBA rather than an optimized one), or that
>> the scheduling program can request specific wrap behavior. A less good
>> option is to take your lumps (missing data) when a wrap happens in the
>> wrong place. But scans cannot be adjusted when that happens in a VLBI
>> schedule.
>>
>> Cheers,
>>
>> Craig
>>
>>
>>
>>
>> Bryan Butler wrote:
>>> amended after some clarification from ken...
>>>
>>>
>>> Bryan Butler wrote, On 3/8/10 09:01:
>>>>
>>>> David Harland wrote, On 3/8/10 08:49:
>>>>> Yes, the OPT allows the user to provide wrap hints for each scan.
>>>>> The scan's default is "No Preference"; the user may change this
>>>>> to CW or CCW.
>>>>>
>>>>> The script generation process sets the wrap for every scan, using
>>>>> -1 for CCW, +1 for CW, and 0 for no-preference.
>>>>>
>>>>> Questions:
>>>>>
>>>>> 1. Should we do as Ken suggested and suppress the
>>>>> subarray.setWrap cmd if the user expressed no preference?
>>>> seems to me the thing to do is:
>>>>
>>>> 1. do a subarray.setWrap(0) at the top of the script
>>>> 2. only do a subarray.setWrap(I) on a scan where it was changed
>>>> from the default by the user in the OPT
>>>
>>> 3. on the subsequent scan, do a subarray.setWrap(0)
>>>
>>>
>>>> (this is probably what ken suggested...)
>>>>
>>>>
>>>>> 2. Is there any harm in sending the same setWrap cmd
>>>>> (eg, setWrap(-1)) on successive scans, as we do
>>>>> currently?
>>>> there is no harm as long as the behavior is as i just described above
>>>> (i.e., the setWrap() has the same parameter as the last scan in
>>>> which it
>>>> was specified).
>>>>
>>>>
>>>>
>>>>>
>>>>> Bryan Butler wrote:
>>>>>> we have always in the past left it up to observers to figure out
>>>>>> whether it is important to them or not. we may not be able to
>>>>>> continue to do that, but for now that is the working model.
>>>>>>
>>>>>> there is no place that the wrap choice is made outside explicitly
>>>>>> setting it in the OPT. if you don't set it (or set it explicitly to
>>>>>> "don't care") then the executor makes the decision about which way to
>>>>>> turn the antennas (i believe the algorithm is a direct copy of what
>>>>>> was done on the modcomps).
>>>>>>
>>>>>> in the future, we can do all sorts of fancy things. in the future...
>>>>>>
>>>>>> -bryan
>>>>>>
>>>>>>
>>>>>> Steven T. Myers wrote, On 3/6/10 13:14:
>>>>>>
>>>>>>> If we are to not have issues like this for routine dynamic
>>>>>>> observing,
>>>>>>> then we at least need a way to make sure all antennas are in the
>>>>>>> same
>>>>>>> wrap (whatever the executor or scheduler decides at the time the
>>>>>>> wrap
>>>>>>> should be). Where is it that the wrap choice (barring explict
>>>>>>> setting
>>>>>>> in the OPT) is made?
>>>>>>>
>>>>>>> Things are usually more deterministic if you observe (ie. get on
>>>>>>> source at least) a source that is well south of the zenith so it it
>>>>>>> guaranteed to not be the ambiguous wrap zones, but I don't know if
>>>>>>> we want to go as far as recommending this to observers.
>>>>>>>
>>>>>>> In the longer term, if we don't go to full dwell-time scheduling, it
>>>>>>> might be prudent to have a parameter like "min_dwell_on_source" that
>>>>>>> is passed to the
>>>>>>> scheduler so it can evaluate whether to execute a given schedule at
>>>>>>> a given
>>>>>>> LST or not (the moral equivalent of running OBSERVE and seeing if
>>>>>>> you get
>>>>>>> enough time on all the sources). This at least might prevent the
>>>>>>> worst problems from slews and wrapping without requring the user to
>>>>>>> over-specify
>>>>>>> start times.
>>>>>>>
>>>>>>> -s
>>>>>>>
>>>>>>> On Fri, 5 Mar 2010, Bryan Butler wrote:
>>>>>>>
>>>>>>>
>>>>>>>> the OPT definitely allows one to set the wrap if desired.
>>>>>>>>
>>>>>>>> -bryan
>>>>>>>>
>>>>>>>>
>>>>>>>> Ken Sowinski wrote, On 3/5/10 17:45:
>>>>>>>>
>>>>>>>>> On Fri, 5 Mar 2010, Vivek Dhawan wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> I just got done with a cursory look at the C55258.434 (AH1004)
>>>>>>>>>> chunk, it looks good on the targets; but the flux cal scan
>>>>>>>>>> 1331+3030
>>>>>>>>>> is fringeless on 6 (otherwise good) antennas even though it is
>>>>>>>>>> 4:15 long
>>>>>>>>>> and most antennas got 1:30 or so dwell time. This should be
>>>>>>>>>> repeated
>>>>>>>>>> with 1331 adequately scheduled, perhaps by moving it a bit later
>>>>>>>>>> in the
>>>>>>>>>> schedule
>>>>>>>>>>
>>>>>>>>> The fringeless antennas are clearly a wrap problem. Whether
>>>>>>>>> it is an observer oversight or a loss of information in
>>>>>>>>> script generation I cannot tell. The OPT allows wrap hints?
>>>>>>>>> The scripts in question had every scan marked as 'dont-care-
>>>>>>>>> about-wrap'.
>>>>>>>>>
>>>>>>>>> I suggest the script generator not include setWrap() calls
>>>>>>>>> unless the observer has supplied an explcit hint to the OPT.
>>>>>>>>> _______________________________________________
>>>>>>>>> evlatests mailing list
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>>>>>>>>>
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>>>>>>>>
>>>>>>> -------------------------------------------------------------------------
>>>>>>>
>>>>>>>
>>>>>>> |:| Steven T. Myers |:| Tenured
>>>>>>> Astronomer |:|
>>>>>>> |:| National Radio Astronomy Observatory |:| Ph: (575)
>>>>>>> 835-7294 |:|
>>>>>>> |:| P.O. Box O, Socorro, NM 87801 |:| FAX: (575)
>>>>>>> 835-7027 |:|
>>>>>>> |:| http://www.aoc.nrao.edu/~smyers |:|
>>>>>>> smyers at nrao.edu |:|
>>>>>>> -------------------------------------------------------------------------
>>>>>>>
>>>>>>>
>>>>>>>
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