ISO cadences

[Frederic V. "Rick" Hessman]

>> The complications for temporal searching are several.  First, you
>> need to be able to search in a barycentric (or arbitrary) time
>> system.  Second, you need to be able to search through some sort of
>> evenly gridded comb filter in cadence - something like "return all
>> images/spectra whose mid-exposure occurred near an even quarter-
>> hour".  Third, you have to be able to specify "near" - "within a
>> window of plus or minus one minute".  Fourth, you may need to be
>> sensitive to some very creative observing modes and data structures.
>> SONG also experimented with a multiple ramped exposure mode for
>> acquiring a time sequence of spectra in a single exposure.  Makes me
>> wonder further about searching for off-band data from dual exposure
>> nod-and-shuffle observations from instruments such as MARS on Kitt
>> Peak.  The second field is shifted both spatially and temporally
>> (interleaved as with any chopping or beam switching mode).
>
>> ISO 8601 provides (as a central design feature) a simple way to
>> specify cadences on a wide range of timescales, i.e., so many seconds
>> or tens of seconds, minutes, hours, days, (even weeks, I believe),
>> months, years, centuries, etc.
>
> Does this imply that a single ISO8601 argument can handle the  
> selection for
> your use-case above?

FYI:   ISO8601 has the following structures:

	DateTime, e.g. UTC			2006-04-26T12:34:56Z
	Duration, e.g.				P1Y2M3DT4H5M6S  (1 year, 2 months, 3 days,....)
	Interval, e.g.
			duration				{duration}
			start+stop			{dateTime#1}/{dateTime#2}
			start+duration		{dateTime}/{duration}
			duration+end		{duration}/{datetime}
	Repeating Interval			R{no. of times}/{interval_as_above}

so, no, there's no error budget which one can build in and still be  
ISO 8601.   On the other hand, the error budge could be added in if  
one defines repeating intervals as

	R{no. of times}/{datetime_start}/{duration}/{errorbudget_duration}


FYFI: RTML does this via

	PhaseConstraint
		Description (a string)
		PhaseTime (an ISO dateTime)
		PhasePeriod (an ISO duration)
		PhaseStart (a double)
		PhaseEnd (a double)
		PhasePdot (a double)	

if one thinks in phases and wants something between PhaseStart and  
PhaseEnd or via

	SeriesConstraint
		Count (a positive integer)
		Description (a string)
		Interval (an ISO duration)
		Tolerance (an ISO duration)

if one thinks in time and wants something at a time +/- a time  
tolerance.

Rick