Tout simplement parce-que il n’existe pas de variable CDI (NAV/GPS)  dans le SDK de P3D, FSX, FS9.
>>Sur un vrai GPS de bord la fonction nearest est bien différenciée de la CDI...c'est claire que JacquesZ a raison mais une simulation reste une simulation 

 .
Juste pour faire un teste si tu a un bouton joystick disponible et FSUIPC enregistrer ouvre dans P3D en fonctionnement,  addons FSUIPC (boutons + Switches) menu déroulant  clique sur (GPS NEAREST BUTTON) ensuit OK, fermer FSUIPC, normalement ça doit fonctionner.

Il te restera a bidouiller pour faire après ce que tu veut avec ton GPS.
Voir aussi pour l'antivirus ici: 
viewtopic.php?f=88&t=6296et aussi : 
viewtopic.php?f=16&t=6063&start=50#p81753A+
Jacques 

PS: ma configuration RealityXP.GNS.ini
- Code: Tout sélectionner
- [GNS_530_1]
 ; is the master device if true.
 MasterDevice = true
 ; selects COM/NAV Radios '1' or '2'.
 RadiosPair = 1
 ; uses computer time if true, simulator time otherwise.
 ComputerTime = false
 ; connects GPS to Autopilot if true.
 LinkOto = true
 ; connects GPS to HSI if true.
 LinkHsi = true
 ; connects GPS to HSI course motor if true.
 LinkCrs = false
 ; connects GPS to OBS input if true (LinkHsi/OBS or AutoNavSource/OBS) (NB: HSI/OBS = NAV1 OBS).
 LinkObs = false
 ; connects GPS to VOR if true.
 LinkVor = false
 ; override VLOC NAV# (1 or 2) or use 'RadiosPair' (0).
 AutoNavSource = 0
 ; connects CDI mode to NAV/GPS switch if true.
 AutoNavGps = true
 ; HSI lateral deviation scale factor.
 CdiScale = 1
 ; HSI vertical deviation scale factor.
 GsiScale = 1
 ; enables Shadin Air Data computer if true.
 UseAirData = true
 ; enables Shadin Fuel Data computer if true.
 UseFuelData = true
 ; enables RYAN 9900BX TCAD if true.
 UseRyanTcad = false
 ; sets TCAD sound alerts volume in percent: 0 to 100.
 RyanTcadVolume = 50
 ; connects GPS #1 to GPS #2 if true (both required).
 UseCrossFill = false
 ; enables device failures if true.
 UseFailures = false
 ; uses Simulator GPS commands if true.
 UseSimGpsCmds = true
 ; updates Simulator GPS flight plan if true.
 LinkSimGps = false
 ; saves the active route as a flight plan file if true (.PLN)
 AutoSavePln = false
 ; uses legacy mouse (left CCW, right CW, middle Push) (override instances settings)
 UseAltMouse = false
 ; uses legacy GNS WAAS 3rd party aircraft panel variables (L:Vars).
 UseLegacyVars = false
 ; sets fuel type: AVGAS,JETA,JETB
 FuelType = AVGAS
 ; sets device power knob switch mode: NONE,DEFAULT_ON,DEFAULT_OFF
 PowerKnob = NONE
 ; sets device power source:
 ; ALWAYS_ON,AVIONICS_ON,PANEL_ON,BUS_MAIN,BUS_AVIONICS,BUS_BATT,BUS_HOTBATT,BUS_1,BUS_2,BUS_3,BUS_4
 PowerSource = AVIONICS_ON
 ; sets TAWS type: TERR,TAWS
 TawsMode = TERR
 ; sets TAWS surface: HARD,HARD_SOFT,WATER,ANY
 TawsSurface = HARD_SOFT
 ; TAWS minimum runway length (feet)
 TawsMinLength = 40
 ; integral lighting percent (0 to 100) or index (-1) (using rxp.panel.rheostat_screen)
 Rheostat.Display = 100
 ; integral lighting percent (0 to 100) or index (-1) (using rxp.panel.rheostat_integral)
 Rheostat.Buttons = 75
 ; sets master sound volume in percent: 0 to 100.
 MasterVolume = 100
 ; mute sound when simulator window looses focus if false.
 NoAudioFocus = false
 ; sets trainer process CPU: 1 to 32 (0: last core, -1: automatic).
 CpuAffinity = -1
 ; cdi/obs: CDI Key (0: disable)
 AFMS.cdi_key =
 ; cdi/obs: Selected Course for GPS (0: disable)
 AFMS.sel_crs_gps =
 ; cdi/obs: Selected Course for VLOC (0: disable)
 AFMS.sel_crs_vloc =
 ; cdi/obs: V-Flag State (1: declutter)
 AFMS.v_flag_declutter =
 ; main: GPS Selected (0: prompt)
 AFMS.gps_selected =
 ; main: COM Presets (1: enable)
 AFMS.com_presets =
 ; connects to: 'PFC_STACK','PFC_430','PFC_530' or any '#PID' (#D002 for PFC_430)
 ; no value connects to first found, 'OFF' disables connection.
 HardwareDevice =
 ; hardware selector number or -1 to disable.
 HardwareIdx = -1
 
 [GNS_530_1.DEFAULT]
 ; show screen only gauge if true.
 nobezel = true
 ; screen only border size (pixels).
 border.size = 0
 ; screen only border color (#RGB or #RGBA).
 border.rgba = #000000
 ; display mouse tooltips if true.
 tooltips = false
 ; enable mouse clickspots if true, disable if false.
 usemouse = true
 ; enable alternate click-spots (left CCW, right CW, middle Push) if true.
 usealtmouse = false
 ; auto-resize dimension (width,height)
 refsize =
 ; left mouse button on the screen toggles popup window by ident (ex: GPS_PANEL or 225).
 popleft =
 ; right mouse button on the screen toggles popup window by ident (ex: GPS_PANEL or 225).
 popright =
 ; adjust brightness (0 to 100)
 brightness.bezel = 100
 ; offset brightness (-100 to +100)
 brightness.screen = 0