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AI Traffic (view source)

Revision as of 10:33, 12 May 2020

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Pusback Tips and Tricks
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(Pusback Tips and Tricks)
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=== A technical perspective ===
=== A technical perspective ===
A ground network file consists of four major sections:
A ground network xml file consists of four major sections:
* The first section is optional, although recent versions of TaxiDraw add this section automatically. This section contains a list of all the radio frequencies for the airport in question. FlightGear currently (as of 1.9.0) uses these frequencies to display some ATC messages. As of FlightGear 1.9.0, only startup approval requests are implemented. You can "hear" these by tuning to the first ground frequency listed in the frequencies section.  
* The first section is optional, although recent versions of TaxiDraw add this section automatically. This section contains a list of all the radio frequencies for the airport in question. FlightGear currently (as of 1.9.0) uses these frequencies to display some ATC messages. As of FlightGear 1.9.0, only startup approval requests are implemented. You can "hear" these by tuning to the first ground frequency listed in the frequencies section.  
* The second section of the file contains the parameters of the airport's parking locations.
* The second section of the file contains the parameters of the airport's parking locations.
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==== Refining the network: Pushback routes ====
==== Refining the network: Pushback routes ====
With the above-mentioned refinements, the ground network should be fully working with one notable exception. Aircraft will be driving forward when leaving the gate, making a sharp turn (while probably destroying themselves and the terminal building in the process). To prevent this, a ''push back'' route should be created. A push back route consists of at least one or more taxiway segments that have the "PushBack Route" property set to true. The last of these segments should be terminated by a PushBack HoldPoint network node.  
With the above-mentioned refinements, the ground network should be fully working with one notable exception. Aircraft will be driving forward when leaving the gate, making a sharp turn (while probably destroying themselves and the terminal building in the process). To prevent this, a ''push back'' route should be created. A push back route consists of at least one or more taxiway segments that have the "PushBack Route" property set to true. The last of these segments should be terminated by a PushBack HoldPoint network node. Pushback routes are optional (if you like the terminal crashing scenario described above).


Notice that a push back route is optional, but that parking spaces may never have more than one push back route. The formal criteria for a valid push back route is that each gate should have a maximum of one push back node associated with it, which can be reached using one route only. From an editing point of view, it is sufficient to just mark a number of taxiway segments as push back, and mark the ending node as such as well.
[[File:Roll Forward Gate in Taxidraw.jpg|thumb|Invalid Park Pos Exist route : at and angle with Parking Position]]
===== Pushback Holding Points must be unique per Parking Position =====


It is important to note that the "Verify Ground network" process ''should be run'' in order to get a correctly working push back system, because this function runs some internal consistency checks. Push back routes can be very simple, from just one route segment, to fairly complex, as illustrated below. Shown here are 3 examples from the EHAM ground network. 1) Shows a fairly complex example, where all aircraft from one side of the E terminal are being linked to one shared push back point. In the example, the push back route of an aircraft departing from gate E20 is illustrated. 2) Shows a simple example, where one aircraft is being pushed back, and makes a left turn. In essence, 3) shows a similar example, but now in a slightly more crowded space, where push back nodes are overlapping. The current push back system allows for fairly complicated behavior. To get a full understanding of it's workings, it is advisable to play with some of the existing ground networks. EHAM and KFSO currently provide the most complex setups.  
Each Parking space (ParkPos) can't have more than one push back route and one pushback holding point at the end of the route. Nevertheless, multiple Parkpos can share part of their pushback routes and a single Pushback Holding Point.
The formal criteria for a valid push back route is that each gate should have a maximum of one push back holding point associated with it, which can be reached using one route only.
From an editing point of view, mark all segments between your parking position and its final holding point as "push back", do not forget to mark the ending node as Pushback Holding Point.


Finally, please notice that you need a version of TaxiDraw with a build date of February 5, 2009, or later, for this to work correctly. Earlier version did not export the pushBackRoute attribute correctly. Support for this functionality was introduced late January 2009, but versions earlier than February 4 contain a potentially fatal bug, that may seriously damage your work.
===== The AI code does not handle sharp angles =====


[[File:TaxiDraw2.png|500px]]
Add nodes to smoothen your routes so that no consecutive segments form an angle of less than 90 degrees.
This rule applies to both pushback and roll forward / taxiways routes
 
===== The Inbound route and the outbound routes are parallel =====
[[File:On Taxiway Pushback Holding Point in Taxidraw.jpg|thumb|Invalid Groudnet Pushback : Holding Point on Taxiway]]
 
The last segment of the pushback route will condition the aircraft heading:
 
1. During its travel along the pushback route
 
2. At the Pushback Holding point (whilst waiting for clearance)
 
3. On departing the pushback holding point, rolling forward to the runway.
 
 
You can not control/force an AI aircraft to leave a Pushback Holding point at a different angle/heading than the one it came onto its final holding node at, whatever the number of routes you add.
 
As a result, the last segment of the pushback route must align with the segment you expect the aircraft to use when starting to roll forward after clearance. The simpler set up is to have this final pushback segment overlapping the first segment of the roll forward route.
 
Alternatively, the last segment of the pushback route can -itself- be the first segment of the roll forward route but this means Traffic Manager will consider this segment 'reserved' whilst the aircraft is pushing back and no other aircraft will be able to use the taxiway.
 
For the same reason the Pushback Holding point should NOT be directly placed on the taxiway as shown in the image on the right 'On Taxiway Pushback Holding Point in Taxidraw'.
Using this particular configuration, once the aircraft 'cleared for taxi', it will ignore the taxiway segments on its left and right and keep its heading, rolling forward towards the original parking position, then 'get lost' and start spinning around, looking for a node to re-anchor to.
 
The "Roll Forward on my current heading" rules also applies to Parking position with no pushback route. These are often used for smaller propeller aircrafts which "pivot" on their parking position before rolling forward. You cannot currently replicate this pivot behaviour in Flightgear AI
 
 
'''Examples of simple valid pushback routes''' (Left: If the taxiway is bidirectional | Centre: If the taxiway is not bidirectional | Right: With shared Pushback Holding point)
 
[[File:MultiDirectionnal Pushback Route in Taxidraw.jpg|400px|Valid AI Groudnet pushback for  multi directional taxiway]]
[[File:UniDirectionnal Pushback Route in Taxidraw.jpg|400px|Valid Pushback Route on Un directional taxiway]]
[[File:Shared Pushback Holding Point in Taxidraw.jpg|400px|Shared Pushback Holding Point]]
 
 
It is important to note that the Taxidraw "Verify Ground network" process ''should be run'' in order to get a correctly working push back system, because this function runs some internal consistency checks. Push back routes can be very simple, from just one route segment, to fairly complex, as illustrated below with all aircraft from one side of the E terminal are being linked to one shared push back point.
 
Given the current push back system allows for fairly complicated behavior it is advisable to test extensively your groundnet and play with various configurations before sharing it to the community.
 
Taxidraw note: TaxiDraw versions prior to February 5 did export the pushBackRoute attribute correctly.
 
[[File:TaxiDraw2.png|thumb]]


==== Verifying the network ====
==== Verifying the network ====
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