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6 Sensor Planning Service – Abstract Overview
6.1 Introduction
The operational context of the SPS is abstracted from, and therefore applies to, several areas of interest. In the scientific area there is a constant interplay between facts, and
theories that explain the facts, which then gives rise to the need for more information in order to confirm and extend the theories. Similarly, in the medical area symptoms give
rise to a need for information that calls for tests that support diagnosis. In the military area there is always a great deal that is unknown about a battle space, or about a theatre
of operations other than war, which gives rise to needs for specific useful information. In the business area corporations and other non-governmental organizations have a need for
global economic intelligence.
All of these areas have information needs, and the SPS is used to task assets to satisfy those needs. The SPS provides an interface to parameterize assets and asset management
systems. It can be applied whenever a client is allowed to influence the internal processes of such a system. The SPS does not provide direct access to the information gathered by
the system itself. This will be done via a SOS or some other OGC Web service. It rather serves as an interface layer to the parameterization interface of the underlying system
see Figure 2.
Figure 2 — SWE Interface of an Asset Management System
The SPS is an interface to a system of any complexity. The system itself is considered as a black box. In this black box, some sort of process gets executed that can be manipulated
by setting specific parameters.
Example: a webcam takes pictures every minute. The SPS interface to this webcam allows modifying this time interval to anything between 10sec and 1hr.
Example: A more complex example is that of a satellite. The SPS interface allows to set a number of parameters, such as region of interest, time of interest, incidence angle with azimuth and elevation, ground resolution etc.
It is up to the SPS provider to define which parameterization options are available to clients via the SPS interface of the given service.
A system operator may even decide to have a chain of SPS instances to provide different capabilities to different types of users for the very same asset.
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Example: Consider the webcam again. Authorized users may change the looking angle and the zoom value, whereas non-authorized users can only chose between three pre-defined settings.
This concept of abstraction levels is described in more detail in section 6.5.
6.2 Client Server Interaction
This section explains the typical interaction between an SPS client and service. The interaction starts with the GetCapabilities request to explore what the service can
offer. If additional information about a sensor is required, the DescribeSensor operation is used to retrieve all available information about the sensor see Figure 3.
Figure 3 — client server interaction part 1
Next, the client needs to learn which parameters have to be set in order to task the sensor. The client sends a DescribeTasking request and receives a DescribeTaskingResponse,
which defines syntax and semantic of each tasking parameter, including choices between different parameter settings, default values, and value ranges.
Note: For complex missions, a huge number of parameters might need to be set by clients. Alternatively, the service might only provide a choice between five preconfigured missions, and then there might only be
a single parameter to be set by clients, even though the missions are very complex in nature. It fully depends on the service provider to define the parameters the client shall or may set. The definition of
tasking profiles is encouraged to reflect the specific requirements of different communities in a consistent way. Nevertheless, tasking parameters are encoded using SWE Common and the SPS provider should add
semantic annotation to them. This allows generic SPS clients to display more specific parameter descriptions including their semantic annotations so that a client can still meaningfully task an asset even if
the client software does not provide any other support for this activity which client software that was specifically developed to support certain tasking profiles will most probably do.
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