Introduction Retrieving a time series Harvester algorithm

OGC Engineering Report OGC 13-053r1 17

4.3 Sequence diagrams

4.3.1 Introduction

The following sequence diagrams illustrates how to obtain a time series for a specific feature of interest and also illustrates the Harvester algorithm see 4.3.3 used to obtain the last observed value for a procedure, which is loaded into the system catalogue.

4.3.2 Retrieving a time series

The following sequence diagram see Figure 2 illustrates how to retrieve a time series from an SOS that is compliant with the NRCan profile. Figure 2 – Sequence diagram for fetching a time series

4.3.3 Harvester algorithm

The following sequence diagram illustrates the harvesting algorithm that is used to populate the catalogue with the last observed value of an observable. The metadata that needs to be gathered by the harvester and stored in the catalogue includes the URL of the sensor observation service, the feature of interest, the observable, its last value and the timestamp. The harvesting algorithm see Figure 3 proceeds as follows: OGC Engineering Report OGC 13-053r1 18 ฀ The harvester module uses the GetCapabilities request to determine the available observables and their extents observedArea. ฀ Using a GetFeatureOfInterest request, the harvester gets all the features of interest using a BBOX over the entire AOI. ฀ For each returned feature of interest, the GetDataAvailability request is used to determine the parameter values necessary to formulate a GetObservation request to read the last value. ฀ The GetObservation request is executed to extract the last value. ฀ The last value is stored in the catalogue along with the URL of the service, the FOI, the observable, the last value and a timestamp. Figure 3 – Sequence diagram for the harvester algorithm It should be noted that the AOI can be segregated into sub-regions and the entire last value harvesting method can be parallelized. That is, multiple harvesters can be running processing sub-regions of the AOI thus allowing the harvesting process to be scaled as required. OGC Engineering Report OGC 13-053r1 19 4.3.4 SOS operations 4.3.4.1 Introduction