Get Latest

Introduction

Getting the latest value of an observation is an important functionality of an observational system. For illustration, consider the  display of  real time status of sensors deployed in a region of interest, with their latest observations. The SOS specification doesn’t provide information about how to perform such an operation, however. The questions that this section addresses is,  ”How do we get the value with the latest time in SOS/SWE specifications?”, or ”How do we get the latest time in an interval?”, or “How do we obtain the latest observation(s)  before a given time T?”

The following schemas were investigated, which do not reveal a best or proposed practice to get the latest observation:

• sos/1.0.0/sosGetObservation.xsd
• (GetObservation/eventTime)
•  gml/3.1.1/base/temporal.xsd
• (RelatedTimeType/relativePosition=[Before|After|Begins|Ends|During|Equals|Contains|Overlaps|Meets|OverlappedBy|MetBy|BegunBy|EndedBy])
• (TimeInstant, TimePeriod (with begin, end, and a duration), TimeInterval, TimePosition)
• (TimeIndeterminateValueType=[after|before|now|unknown])
• sos/1.0.0/ogc4sos.xsd
• (TemporalOpsType=[TM_Before|TM_After|...|TM_EndedBy])
• {note typo in line 29, 'TM_Overalps' spelling}

It became clear in the course of discussion between OCEANS IE and SWE working group participants that the desired results are actually not about time constraints, but about ordering and limiting the result set. The desired GetLatest capabilities can be achieved with a specification that describes the ordering of results, and how many to return (e.g., 'descending time', and '1'). To get the nearest time would require introducing the concept of 'nearest', or an absolute distance from the specified time period or instant. (Similar capabilities would be needed to find the spatially nearest sample along a given dimension.)

Best Practice: The Oceans IE team decided on an interim practical solution by agreeing on a default behavior of the servers. If there is no time specified in the request getObservation, the response will supply the latest known observation. One observation per procedure.

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Revision History

Date	Editor	Changes
2008-12-16	Luis Bermudez	1 version

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TODOs

Date	Requester	TODO