SPI – System point Of Interest
SPI Description
SPI – System point Of Interest, as its name implies, is the point on the ground where (usually) the AG system is Concentrated. The SPI position can be determined (or controlled) by 2 sensors:
- GM/GMT/Sea radar in STP mode.
- The Targeting Pod.
Each of these sensors can slave the SPI to where it is pointing according to the avionics and the sensor's mode. The SPI position is then shared between those sensors if conditions fit.
When one of the above sensors is in tracking state (GM radar in FTT or TGP in none slave mode), the SPI is slaved to the tracking sensor. If one of the sensors is in tracking state and the pilot is commanding the other sensor to track as well, then the first sensor will break track automatically and update its position with the SPI (which is slaved to the tracking sensor). It's impossible to have both GM radar and TGP in tracking state at the same time.
If no tracking state exists, slewing the GM radar in STP mode will slew the SPI to the same position which will be shared by the TGP as well. Slewing the TGP in STP mode OTOH will also slew the SPI and the GM radar to the same position. If tracking state exists by either sensor and the other sensor is slewed to a different position then the slewing is local and has no effect on the SPI position which stays with the tracking sensor.
Important note: If one of the sensors is in tracking state and the other is slewed you may think there is weird because the TD box will not move with the slewing sensor but of course that is correct behavior because the TD box is reflecting the position of the SPI which stays with the tracking sensor.
...
En bref ... le "SPI" est le point (géographique, ou dans l'espace) vers lequel pointe les senseurs (ou le senseur sélectionné connu sous le nom de "SOI").
Par défaut, il est confondu avec le point de navigation sélecté, mais on peut lui appliquer des "offset", soit en utilisant les curseurs et en le faisant glisser, soit de façon prédétermine en utilisant les VRP/VIP/OA1/OA2).
Toutes les info de guidage, heure estimé d'arrivé, target box, tadpole etc... seront pointé vers le SPI et non plus vers le point de nav.
Mais les modalités d'utilisation peuvent diverger fonction des modes dans lequel on est et peuvent dépendre le l’armement utilisé (TGP,WPN,FCR,MARKPOINT. etc...)
Il faut bien être conscient le toutes les info de coordonnées TGP, pointage TGP, curseur radar, info dans le HUD, asservissement, sont relatives au SPI, et non plus forcement au point de nav sélecté!
A noter également que deux senteurs utilisés en parallèle mais non asservi l'un à l'autre peuvent avoir deux SPI différent (FCR / TGP par exemple).
Il faudra BIEN faire attention a cela!
Vous verrez les détails plus tard...
. 
