XPMP2

TCAS and AI/multiplayer Support

XPMP2 provides TCAS blibs and AI/multiplayer data using TCAS Override introduced with X-Plane 11.50 Beta 8. Please do read that blog post by Laminar as it explains all what’s necessary and what also XPMP2 does:

• Try acquiring TCAS control via a call to XPLMAcquirePlanes. All what follows only happens if XPMP2 was granted access:
• Sets sim/operation/override/override_TCAS to 1 to tell X-Plane that it will use TCAS Override
• Sets sim/operation/override/override_multiplayer_map_layer to 1 to tell X-Plane that it shall not draw icons into the map as XPMP2 provides a self-defined additional map layer
• All aircraft are sorted by distance (biased by XPMP2::Aircraft::aiPrio), for each aircraft a number of dataRefs are set, see below
• In a call to XPLMSetActiveAircraftCount X-Plane is informed about the exact number of provided planes. (This might not be strictly necessary, but probably a cleaner approach than to wait 10 cylces for not updated dataRefs to be taken out of X-Plane’s consideration.)

When TCS Override is not available (like up to X-Plane 11.41), then TCAS is provided by writing the classic multiplayer dataRefs directly.

Slotting

There is a limited number of “slots” available for TCAS/multiplayer purposes. With TCAS Override, this is currently 63, with classic multiplayer dataRefs, this is up to 19, though for many 3rd party plugins the number of actually configured AI Aircraft (X-Planes Flight Setup) plays a role, too.

XPMP2 will show the aircraft closest to current camera location. This set of aircraft will change over time. But XPMP2 will try to keep a plane, which once was shown on TCAS, in the same slot to make it easier for 3rd party plugins to follow one plane.

Keeping a plane in one slot has limits. The following rules apply:

• TCAS Override (X-Plane 11.50b8 and above): The lower 19 slots are the “lower range” because 3rd party plugins not yet using TCAS Override have access to only these 19.
• Fallback with classic dataRefs: The lower n slots, for which AI Aircraft are configured, are considered “lower range” because some 3rd party plugins only access as many planes as are configured as AI Aircraft (though this is unnecessary: plugins could just read all 19 dataRefs irrespective of what XPLMCountAircraft returns.)
• This “lower range” is considered higher priority and will be filled up first with closest planes.
• XPMP2 will fill a continuous set of slots starting at 1. If a plane is removed, which occupied a slot in the middle then another plane will take it (potentially moving down from the upper range to the lower range).
• Also, if a plane is moved between lower and upper range because it moved ranks in the order by distance, then it changes slots.

TCAS Target dataRefs

XPMP2 writes the folloing TCAS target dataRefs when it has TCAS control:

.../tcas/targets/	XPMP2’s value from XPMP2::Aircraft
modeS_id	modeS_id
modeC_code	acRadar.code
flight_id	what GetFlightId() returns: acInfoTexts.flightNum or acInfoTexts.tailNum or acInfoTexts.aptFrom-acInfoTexts.aptFrom, whatever is available first; this is a virtual function that you can override in your implementation
icao_type	acIcaoType

All dataRefs under sim/cockpit2/tcas/targets/position/ are filled as expected and documented except for weight_on_wheels, for which no value in XPMP2::Aircraft::v is yet available:

Values are taken from XPMP2::Aircraft::v. Compare the indexes as defined in the enum DR_VALS defined in XPMPAircraft.h:

.../tcas/targets/position/	XPMP2’s value from XPMP2::Aircraft
x, y, z	drawInfo.x, drawInfo.y - ac.GetVertOfs(), drawInfo.z
vx, vy, vz	updated once a second with deltas of respective values in drawInfo devided by time passed
psi	drawInfo.heading
the	drawInfo.pitch
phi	drawInfo.roll
flap_ratio	v[V_CONTROLS_FLAP_RATIO]
gear_deploy	v[V_CONTROLS_GEAR_RATIO]
flap_ratio2	v[V_CONTROLS_FLAP_RATIO]
speedbrake_ratio	v[V_CONTROLS_SPEED_BRAKE_RATIO]
slat_ratio	v[V_CONTROLS_SLAT_RATIO]
wing_sweep	v[V_CONTROLS_WING_SWEEP_RATIO]
throttle	v[V_CONTROLS_THRUST_RATIO]
yolk_pitch	v[V_CONTROLS_YOKE_PITCH_RATIO]
yolk_yaw	v[V_CONTROLS_YOKE_HEADING_RATIO]
yolk_roll	v[V_CONTROLS_YOKE_ROLL_RATIO]
lights	v[V_CONTROLS_TAXI_LITES_ON], v[V_CONTROLS_LANDING_LITES_ON], v[V_CONTROLS_BEACON_LITES_ON], v[V_CONTROLS_STROBE_LITES_ON], v[V_CONTROLS_NAV_LITES_ON]
weight_on_wheels	-

Classic AI/Multiplayer support

…is provided by X-Plane automatically when feeding above TCAS target dataRefs. That means: The lower 19 planes are mirrored into the well-known sim/multiplayer/position/plane#_* dataRefs. Plugins still relying on these dataRefs will mainly “just work”. And this without any workarounds like defining AI Aircraft in X-Plane’s settings!

Please note that XPLMCountAircraft can now return values larger than 20, up to 64 at the moment.

XPMP2 still makes sure that unused sim/multiplayer/position/plane# slots (ie. if less than 19 planes are shown) are initialised with _x/y/z set to 9999999.9. They are deliberately not set to 0 if unused, because 0/0/0 is a totally valid local geographic location.

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