The problem with making this configurable is that then nobody will know how
any given GeoServer instance works. I would say that providing both
options should be a last resort if it really ends up to be impossible to
decide on a reasonable interpretation of the spec.
Is it possible to ask OGC what the correct interpretation should be? Are
there CITE tests which clarify this?
And perhaps it's possible to see how other implementations have interpreted
this? CubeWerx for instance?
On Mon, Jul 16, 2012 at 9:31 AM, Justin Deoliveira <[email protected]>wrote:
> Interesting take, and a good argument. On the one hand the spec does seem
> to require the expansion into an interval, and other servers such as
> mapserver have implemented it this way. On the other hand you poke some
> pretty good holes in that heuristic. Maybe this is something worth
> splitting the difference on and making it a configurable option?
>
>
> On Fri, Jul 13, 2012 at 1:30 PM, Ian Schneider <[email protected]>wrote:
>
>> Matt and I were just having a discussion regarding this topic today.
>>
>> While I agree it is a compelling argument to implicitly interpret a
>> non-precise instant request (2012, for example) as a range
>> (2012-2013), I believe it should be avoided in favor of explicit
>> requests. I agree the WMS specs (1.1.1 and 1.3) are somewhat unclear
>> on this, but I believe clarity can be derived from the annex sections
>> C.5.2 and C.4.3 (1.1.1 and 1.3, respectively) that discuss this:
>>
>> """A WMS may declare that it will choose the closest available value
>> for a dimension if an exact value is not
>> specified. This allows, for example, hourly data whose actual
>> recording time is precise to the millisecond to be
>> requested simply by stating the desired date and hour. The
>> nearestValue attribute of the <Dimension> element, if
>> present and nonzero, indicates that this behaviour is enabled."""
>>
>> While this applies more to the 'closest' (snapping) value than to
>> implicit conversion of an instant to an extent, I think the motivation
>> is similar - be explicit and when other behavior occurs, let the
>> client know.
>>
>> Additionally, while it may make sense for certain instants to be
>> interpreted, e.g. 2012 means 2012-2013, it most certainly does not for
>> others, e.g -200000 (most likely the data is imprecise beyond a year).
>> While the implied period approach works well for simple,
>> multiplier-of-1 ranges, may domains use other ranges (10 year, 3
>> month, 6 hour, 30 minute, etc.) and may expect a similar behavior
>> (e.g. 2012-01-01T12:15:00 means 2012-01-01T12:00:00 to
>> 2012-01-01T12:30:00 since the interval of that specific data is 30
>> minute).
>>
>> So, I would argue that according to the spec:
>> 1) 2012 means 2012-01-01T00:00:00Z
>> 2) 2012/2013 means 2012-01-01T00:00:00Z-2013-01-01T00:00:00Z
>> (inclusive on both sides as per the spec)
>>
>> Since most clients of a time aware mapping service will not require
>> the user to type out full-precision or ranges and will perform the
>> requests for the user, these implicit instant-to-extent "short-cuts"
>> can be taken there, but IMHO, don't belong on the server.
>>
>> Cheers,
>>
>> On Tue, Jun 5, 2012 at 5:32 PM, Justin Deoliveira <[email protected]>
>> wrote:
>> >
>> >
>> > On Tue, Jun 5, 2012 at 8:33 AM, Andrea Aime <
>> [email protected]>
>> > wrote:
>> >>
>> >> On Mon, Jun 4, 2012 at 10:21 PM, Martin Davis <[email protected]>
>> wrote:
>> >> > Here's a couple of data points for this discussion:
>> >> >
>> >> > http://mapserver.org/ogc/wms_time.html
>> >> >
>> >> > MapServer has addressed this issue (see the section Interpreting Time
>> >> > Values), but they seem to do different things depending on the
>> back-end
>> >> > data
>> >> > source. For PostGIS at least they use the "time as time window"
>> >> > approach,
>> >> > by virtue of using the DB date_trunc function, which amounts to the
>> same
>> >> > thing). One takeaway from this: I would suggest we want a data
>> >> > source-independent strategy.
>> >> >
>> >> >
>> >> >
>> http://augusttown.blogspot.ca/2010/03/two-ambiguities-about-time-in-ogc-wms.html
>> >> >
>> >> > This blog post discuss the issue, and weighs in on the side of
>> treating
>> >> > all
>> >> > time values as time windows (with duration determined by precision).
>> >> > This
>> >> > seems to make sense to me. Although, what then is meant by a TIME of
>> >> > 2012-06-01/2012-06-02". Is that the window including exactly June
>> 1, or
>> >> > does it include June 1-2 ?
>> >>
>> >> I agree the time window approach makes sense, and yes, the current
>> >> implementation
>> >> switches to a interval only if you explicitly ask for an interval,
>> >> otherwise the time
>> >> elements missing are assumed to be zero (from memory, at least).
>> >
>> > Yup, it expands out by appending the zeros.
>> >>
>> >>
>> >> It may be an easy fix, inside the time kvp parser, if the time is not
>> >> fully specified
>> >> turn it into a interval?
>> >> We already handle t1/t2 as an extension to the wms spec (which would
>> ask
>> >> for
>> >> a third parameter, the period).
>> >
>> >
>> > Agreed, looks like is relatively straight forward and constrained to
>> the kvp
>> > parser. On my todo list to come up with a patch.
>> >>
>> >>
>> >> However... how do we handle a list of values that have no full
>> precision?
>> >> Turn it into a list of intervals? Now, this we don't handle...
>> >>
>> > Yeah, good question. I will hunt through the spec to see if says
>> anything
>> > about that.
>>
>>
>>
>> --
>> Ian Schneider
>> OpenGeo - http://opengeo.org
>> Enterprise support for open source geospatial.
>>
>
>
>
> --
> Justin Deoliveira
> OpenGeo - http://opengeo.org
> Enterprise support for open source geospatial.
>
>
>
> ------------------------------------------------------------------------------
> Live Security Virtual Conference
> Exclusive live event will cover all the ways today's security and
> threat landscape has changed and how IT managers can respond. Discussions
> will include endpoint security, mobile security and the latest in malware
> threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
> _______________________________________________
> Geoserver-devel mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/geoserver-devel
>
>
--
Martin Davis
OpenGeo - http://opengeo.org
Expert service straight from the developers.
------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and
threat landscape has changed and how IT managers can respond. Discussions
will include endpoint security, mobile security and the latest in malware
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
_______________________________________________
Geoserver-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/geoserver-devel
