[webservices] response given known channel start

[Philip Crotwell]

Just to make sure I am doing this correctly...

If I have a known channel start time, say 1995-03-21T17:16:00, then to
limit the returned xml to be just the response for that single channel I
should use endafter and endtime like this:
http://service.iris.edu/fdsnws/station/1/query?network=IU&sta=ANMO&loc=--&cha=BHZ&endafter=1995-03-21T17:16:00&endtime=1995-03-21T17:16:00&level=response&nodata=404

In contrast, if I use starttime andendtime like this:
http://service.iris.edu/fdsnws/station/1/query?network=IU&sta=ANMO&loc=--&cha=BHZ&starttime=1995-03-21T17:16:00&endtime=1995-03-21T17:16:00&level=response&nodata=404

then I get both the channel I want, as well as the one that was operational
immediately before the time I am interested in.

But the docs are confusing as they say that:

      startbefore, endbefore, startafter, endafter

      These criteria are applied at the station level, regardless of which
level is requested or which channel, network, location,
       station filters are used.

Which I think means that my above query should not work, even though it
does seem to, as the time restriction I am trying for is on the channel
times and there was one station operating over this time that had 5
channels, but both of my above queries return fewer (one or two).

The fdsn ws specification doesn't make the way time params are interpreted
very clear as it only says that these 4 times "Limit to metadata
epochs...", but does not say they are limited to the station or in fact
what they are applied to. I am guessing that the iris docs are wrong, but
the fdsn spec also seems incomplete.

The other confusing thing to me is that the iris docs talk about how the
time criteria apply based on whether there is a channel or location or
station parameter and ignores the level parameter, but i dont' see any
similar idea in the fdsn spec. Is this an iris implementation detail, or is
the spec incomplete? I feel like the most natural way is to have the time
criteria apply to the level asked for, but maybe I am missing something.
Some experimentation seems to show that the level param is actually what
controls the time aspect, but not totally sure.

IMHO, this whole starttime, endtime, startsbefore, endbefore, startsafter,
endafter system seems really confusing. All the other systems of querying
this type of data in the past have used a simple start/end window, and the
"effective times" of the channel-like objects were "half open intervals"
that included their begin, but not their end. In math notation, [start,
end), meaning if you asked for an interval where the start/end were the
same, you got the single channel that you likely wanted. I am not sure the
added complexity and non-intuitiveness of these 6 time query parameters is
really worth it.

Can someone clarify how all this is supposed to work?

thanks,
Philip
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.iris.washington.edu/pipermail/webservices/attachments/20130503/4ad8bc82/attachment.htm>