===== Ground Truth Sensor =====

==== What It Is ====

A Ground Truth Sensor (GTS) allows the JAS user to model detections without deploying assets to do the actual detection. For instance, if, in your scenario, you __know__ that you will be able to detect the bad guys crossing some line ([[http://en.wikipedia.org/wiki/Cabot_Strait|the Cabot Strait]]) with some degree of confidence, then you can use a GTS to do the actual detection without having to put a Bse with a sensor near the detection. Although GTS was originally developed to model the static [[http://en.wikipedia.org/wiki/Sosus|underwater listening arrays]] deployed by some of the world's navies, it can be used to model a special satellite, CNN reports, or Humint on the ground.

==== How to use it ====

Create a GTS asset by cloning or creating an asset and then setting its class to Ground Truth Sensor. Then go to the Ground Truth Sensors pane under Sensor and add your newly created sensor by clicking New from the right click menu. The five parameters of a GTS are:
  * Nai Name - this is the footprint of your sensor. The GTS will see only those Bses that are in the NAI. The center point of the GTS is the center point of the NAI. The GTS remains fixed; it does __not__ move with its owning Bse. You must currently use only a circular Nai.
  * Probability of Detection - just what it says
  * Probability of Classification - not currently used
  * Reporting Frequency in hours - this value controls how often the GTS looks at what is inside its NAI.
  * Reporting Delay - this value exists to model any PED delay if desired.

The bottom two panes control what the GTS will look for. It can see every Bse in one or more of the [[jasDomains|JAS domains]], or it can see certain Bse type(s), but not both.

Add the GTS you just created to a Bse. Also add the C2/Plugin named JwGroundTruthC2.

==== How it works. ====

  * The GTS initializes at simulation start. It does this by creating a list of org type interests (really Bse type interests) from the domains or Bse types specified in the Gui. For instance, if you selected the domain GROUND, the GTS's org type interest list would include every Bse that lives in the GROUND domain. 
  * The GTS is a type of Collision Sensor and works by turning on every Reporting Frequency number of hours and asking the Interaction Manager what Bses are in its (Nai) footprint that are also in its list of org type interests. 
  * The GTS sends the addTargets: message to its JwGroundTruthC2. The JwGroundTruthC2 draws a random number for each Bse reported and determines if there is a detection using the value of Probability of Detection.
  * The GTS will respond to new targets entering its footprint, targets changing direction or stopping/starting movement, and targets leaving its footprint, just like all other Collision Sensors.
  * Detections are sent to the owning Bse after the time specified in Reporting Delay has expired.
  * The owning Bse must know how to process sensor detection messages from a GTS sensor. There is no default behavior.

==== How it differs from other sensors ====

  * The GTS remains fixed; it does __not__ move with its owning Bse. The owning Bse can be any Bse anywhere.
  * The GTS will 'glimpse' what is in its footprint every Reporting Frequency number of hours, in addition to reporting new targets entering its footprint, the removal of targets leaving its footprint, and movement changes of target in its footprint.
 

==== Miscellaneous ====
 


  * The name of the GTS will be its asset name, the Nai name, and GroundTruthCollisionSensor concatenated with underscores, e.g., GT_SENSOR_BigNai_GroundTruthCollisionSensor.
  * The behavior of the GTS is instrumented in C4ISR GT Sensor Detections.